Does dark energy accelerate space missions ? ESA has a plan to launch Euclid mission to find more about dark energy.



October 05, 2011


dark energy, ESA, cosmology,

The movie stills pictured above illustrate the formation of clusters and large-scale filaments in the Cold Dark Matter model with dark energy.


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wikimedia commons


Perfect timing: Yesterday, three astronomers received the news every scientist wants: they would be receiving the physics Nobel Prize for their work in discovering dark energy, a repulsive force that is ramping up the expansion of the universe.


So it was somehow fitting that, on the very same day, European Space Agency officials were approving a space mission, called Euclid, that would pin down more precisely dark energy’s key parameters.


“It was just coincidence, really,” says David Schlegel, principal investigator for BOSS, a ground-based mission that is also trying to get a handle on the stuff that looks a lot like a cosmological constant, the fudge factor that Einstein introduced in his relativity equations when he thought the universe was static, but later regretted.


Okay, so the prize has nothing to do with ESA’s decision.


But will it bolster the case for other dark energy missions?


In the United States, NASA, the Energy Department and the National Science Foundation are all trying to get a piece of the action. NASA’s WFIRST is the most expensive mission and the most sought after (it was ranked tops in the US decadal survey), and it’s probably the most capable.



But it’s stuck in line behind the James Webb Space Telescope, and so most observers think it doesn’t have a chance of flying at all until the 2020s.


The selection of Euclid, a very similar mission that would scoop much of the early science, may put further pressure on NASA to attempt what has failed in the past: a mission merger.



Ground-based dark energy experiments may get a lot more bang for the buck -- but even there, money is a problem.



LSST, another community favorite that will make major strides in measuring dark energy, still needs cash.



In a universe that keeps moving faster and faster, missions like LSST and WFIRST seem to get farther and farther away.


“It seems like it’s so far in the future,” says Schlegel.


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Multiverse From Wikipedia, the free encyclopedia


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The multiverse (or meta-universe, metaverse) is the hypothetical set of multiple possible universes (including the historical universe we consistently experience) that together comprise everything that exists: the entirety of space, time, matter, and energy as well as the physical laws and constants that describe them.

The term was coined in 1895 by the American philosopher and psychologist William James.

The various universes within the multiverse are sometimes called parallel universes.

The structure of the multiverse, the nature of each universe within it and the relationship between the various constituent universes, depend on the specific multiverse hypothesis considered.

Multiverses have been hypothesized in cosmology, physics, astronomy, religion, philosophy, transpersonal psychology and fiction, particularly in science fiction and fantasy.

In these contexts, parallel universes are also called "alternative universes", "quantum universes", "interpenetrating dimensions", "parallel dimensions", "parallel worlds", "alternative realities", "alternative timelines", and "dimensional planes," among others.


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Observation of Rare Particles May Shed Light On Why the Universe Has More Matter Than Antimatter


cosmology, antimatter,cern

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ScienceDaily (June 19, 2011) — Shortly after experiments on the Large Hadron Collider (LHC) at the CERN laboratory near Geneva, Switzerland began yielding scientific data last fall, a group of scientists led by a Syracuse University physicist became the first to observe the decays of a rare particle that was present right after the Big Bang.



By studying this particle, scientists hope to solve the mystery of why the universe evolved with more matter than antimatter.

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Antigravity Could Replace Dark Energy as Cause of Universe’s Expansion



anti-gravity,dark energy,cosmology

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Since the late 20th century, astronomers have been aware of data that suggest the universe is not only expanding, but expanding at an accelerating rate.


According to the currently accepted model, this accelerated expansion is due to dark energy, a mysterious repulsive force that makes up about 73% of the energy density of the universe.


Now, a new study reveals an alternative theory: that the expansion of the universe is actually due to the relationship between matter and antimatter.


According to this study, matter and antimatter gravitationally repel each other and create a kind of “antigravity” that could do away with the need for dark energy in the universe.


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NASA Prepares Antimatter-Hunting Detector for Space Shuttle Launch


16 March 2011



cosmologyn,dark matter,AMS,Space Shuttle,ISS

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A high-tech astrophysics experiment that will probe the mysteries of our universe is getting ready to fly to the International Space Station aboard the space shuttle Endeavour when it launches on its final mission next month.

The Alpha Magnetic Spectrometer (AMS) is a particle physics detector that will primarily measure high-energy particles in space, called cosmic rays, and search for signs of antimatter and mysterious dark matter in the universe.


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Dark-Matter Galaxy Detected: Hidden Dwarf Lurks Nearby?


Richard A. Lovett in Seattle, Washington

for National Geographic News

Published January 14, 2011


Milky Way.jpg


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An entire galaxy may be lurking, unseen, just outside our own, scientists announced Thursday.


The invisibility of "Galaxy X"—as the purported body has been dubbed—may be due less to its apparent status as a dwarf galaxy than to its murky location and its overwhelming amount of dark matter, astronomer Sukanya Chakrabarti speculates.


Detectable only by the effects of its gravitational pull, dark matter is an invisible material that scientists think makes up more than 80 percent of the mass in the universe.


Chakrabarti, of the University of California, Berkeley, devised a technique similar to that used 160 years ago to predict the existence of Neptune, which was given away by the wobbles its gravity induced in Uranus's orbit.


Based on gravitational perturbations of gases on the fringes of our Milky Way galaxy, Chakrabarti came to her conclusion that there's a unknown dwarf galaxy about 260,000 light-years away.

With an estimated mass equal to only one percent the mass of the Milky Way, Galaxy X is still the third largest of the Milky Way's satellite galaxies, Chakrabarti predicts.

The two Magellanic are each about ten times larger.

If it exists, Galaxy X isn't likely to be composed entirely of dark matter.

It should also have a sprinkling of dim stars, Chakrabarti said.

"These should provide enough light for astronomers to see it, now that they know where to look," she said.

The reason the dark matter galaxy hasn't yet been seen, she added, is because it lies in the same plane as the Milky Way disc.

Clouds of gas and dust stand between us and Galaxy X, confounding telescopes.




Copyright : http://news.nationalgeographic.com/news/2011/01/110114-ga...



Harvard-Smithsonian Center For Astrophysics - Better Measuring Dark Energy



Press Release

Release No.: 2011-04

For Release: Thursday, January 13, 2011 09:00:00 AM EST


Dark Energy.jpg


Copyright : http://commons.wikimedia.org/wiki/File:Cosmological_compo...


The Best Way to Measure Dark Energy Just Got Better


Seattle, WA


Dark energy is a mysterious force that pervades all space, acting as a "push" to accelerate the Universe's expansion.


Despite being 70 percent of the Universe, dark energy was only discovered in 1998 by two teams observing Type Ia supernovae.


A Type 1a supernova is a cataclysmic explosion of a white dwarf star.


These supernovae are currently the best way to measure dark energy because they are visible across intergalactic space.


Also, they can function as "standard candles" in distant galaxies since the intrinsic brightness is known.


Just as drivers estimate the distance to oncoming cars at night from the brightness of their headlights, measuring the apparent brightness of a supernova yields its distance (fainter is farther).


Measuring distances tracks the effect of dark energy on the expansion of the Universe.


The best way of measuring dark energy just got better, thanks to a new study of Type Ia supernovae led by Ryan Foley of the Harvard-Smithsonian Center for Astrophysics. 


He has found a way to correct for small variations in the appearance of these supernovae, so that they become even better standard candles.


The key is to sort the supernovae based on their color.


"Dark energy is the biggest mystery in physics and astronomy today.


Now, we have a better way to tackle it," said Foley, who is a Clay Fellow at the Center.


He presented his findings in a press conference at the 217th meeting of the American Astronomical Society.


The new tool also will help astronomers to firm up the cosmic distance scale by providing more accurate distances to faraway galaxies.


Type Ia supernovae are used as standard candles, meaning they have a known intrinsic brightness.


However, they're not all equally bright.


Astronomers have to correct for certain variations.


In particular, there is a known correlation between how quickly the supernova brightens and dims (its light curve) and the intrinsic peak brightness.


Even when astronomers correct for this effect, their measurements still show some scatter, which leads to inaccuracies when calculating distances and therefore the effects of dark energy.


Studies looking for ways to make more accurate corrections have had limited success until now.


"We've been looking for this sort of 'second-order effect' for nearly two decades," said Foley.


Foley discovered that after correcting for how quickly Type Ia supernovae faded,

they show a distinct relationship between the speed of their ejected material and their color: the faster ones are slightly redder and the slower ones are bluer.


Previously, astronomers assumed that redder explosions only appeared that way because of intervening dust, which would also dim the explosion and make it appear farther than it was.


Trying to correct for this, they would incorrectly calculate that the explosion was closer than it appeared.


Foley's work shows that some of the color difference is intrinsic to the supernova itself.


The new study succeeded for two reasons.


First, it used a large sample of more than 100 supernovae.


More importantly, it went back to "first principles" and reexamined the assumption that Type Ia supernovae are one average color.


The discovery provides a better physical understanding of Type Ia supernovae and their intrinsic differences.


It also will allow cosmologists to improve their data analysis and make better measurements of dark energy - an important step on the road to learning what this mysterious force truly is, and what it means for the future of the cosmos.


Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.


Copyright : http://www.cfa.harvard.edu/news/2011/pr201104.html



Cosmology - animation photo from Big Bang To Present Time



Doorbraak of gelul in de ruimte ?


25 september 2010

de Volkskrant 

De Amerikaanse natuurkundige Greg Landsberg zegt een nieuwe theorie over verdwijnende ruimtelijke dimensies te hebben gevonden die het antwoord zou kunnen verschaffen op allerlei netelige vragen.


Nederlandse collega's regeren geërgerd. 'Toe maar, dit kan er ook wel bij.'

‘Een nieuw paradigma’ noemt hij het zelf. Speculatief, jazeker, maar daarom niet minder veelbelovend.


Greg Landsberg, natuurkundige aan de Amerikaanse Brown University, raakt er niet over uitgepraat.


Samen met vier collega’s leurt hij sinds een paar maanden met het idee dat het aantal ruimtelijke dimensies in het heelal afhankelijk is van de schaal waarop je de dingen bekijkt.


‘Misschien levert dit een oplossing voor allerlei netelige kwesties in de deeltjesfysica en de kosmologie,’ ratelt hij over de telefoon vanuit deeltjeslaboratorium CERN in Genève. ‘En wie weet lossen we het raadsel van de tijd er ook wel mee op.’


Netelige kwesties zijn er volop in de moderne natuurwetenschap. Waarom zijn er bijvoorbeeld drie deeltjesfamilies in plaats van één?


Wat is zwaartekracht? Waarom is er meer gewone materie dan antimaterie in het heelal? Hoe komt het dat het heelal steeds sneller uitdijt?


Waaruit bestaat de mysterieuze donkere materie? Valt de relativiteitstheorie ooit te rijmen met de quantumfysica?


En, inderdaad, wat is tijd eigenlijk? Wie het allemaal weet, mag het zeggen.


En wie het niet weet, hoeft kennelijk ook zijn mond niet te houden.


De meest uiteenlopende modellen, theorieën, concepten en luchtballonnetjes vinden de laatste jaren hun weg naar wetenschappelijke blogs, preprint servers, of zelfs naar de pagina’s van Physical Review Letters. Een vijfde kracht, schaduwmaterie, asymmetrische branen – het komt allemaal voorbij.


De onbewijsbare snaartheorie met zijn 10^500 heelallen, stevig gepromoot door niemand minder dan Stephen Hawking, is eigenlijk nog een van de serieuzere ideeën.


Van de ‘verdwijnende dimensies’ van Landsberg en zijn collega’s kijkt een theoretisch fysicus nauwelijks meer op.


‘Buitengewoon onaangenaam’ vindt kosmoloog Vincent Icke van de Leidse Sterrewacht deze wildgroei aan ‘loze speculaties’.


‘Ik sta positief tegenover dwarse denkers,’ zegt hij, ‘maar je moet wel met een verdomd goed onderbouwd idee komen, wil ik het serieus nemen.


Nu nemen mensen onbeperkt de vrijheid om maar te zeggen wat ze blieven.


Neem dat snaargelul, daar is al dertig jaar niets uitgekomen dan gebakken lucht en af en toe een wiskundeprijsje.


Ik vind dat laf.’ Theoretisch natuurkundige Gerard ’t Hooft van de Universiteit Utrecht, op werkbezoek in Turkije, is het met Icke eens.


‘Men schrijft er maar op los,’ mailt de Nobelprijswinnaar. ‘Verdwijnende dimensies, toe maar, het kan er ook wel bij.’



Landsberg – in 1967 in Moskou geboren – ziet dat natuurlijk heel anders. Er zijn inderdaad meer theorieën dan theoretici, grapt hij met een licht Russisch accent, maar nieuwe ideeën die misschien bevestigd zouden kunnen worden door toekomstige experimenten, kun je niet zomaar negeren.


Afgelopen zomer, tijdens de International Conference on High-Energy Physics in Parijs, was er weliswaar veel kritiek op het ‘nieuwe paradigma’, maar toch vooral veel belangstelling. Geen wonder, aldus Landsberg, want wie weet komt de nieuwe deeltjesversneller van CERN nog dit jaar met ondersteunende resultaten.


Dun rietje


Begin vorige eeuw speculeerden Theodor Kaluza en Oskar Klein al over extra dimensies, in een vruchteloze poging om zwaartekracht en elektromagnetisme in één beschrijving te verenigen.


Volgens de Kaluza-Kleintheorie bestaat er naast lengte, breedte en hoogte een vierde ruimtelijke dimensie.


Die zou echter niet oneindig uitgestrekt zijn, maar heel compact, waardoor je er alleen op miscroscopische schaal mee te maken krijgt.


Alsof je een eendimensionale lijn ziet, die bij nadere beschouwing een tweedimensionaal oppervlak blijkt te zijn, heel strak opgerold tot een extreem dun rietje.


‘In ons model is er echter geen sprake van extra dimensies, maar van ‘verdwijnende’ dimensies,’ zegt Landsberg.


Hoe nauwkeuriger je kijkt, hoe minder ruimtelijke dimensies er zijn.


Precies andersom dus dan bij Kaluza en Klein. Op een natuurkundeworkshop in Heidelberg, vorig jaar zomer, begon het balletje te rollen.


‘Tijdens een etentje met twee andere natuurkundigen en twee kosmologen bleek dat die vanishing dimensions wel eens een verklaring zouden kunnen vormen voor een aantal problemen in de moderne natuurwetenschap.’


Om uit te leggen hoe het werkt, vergelijkt Landsberg de ruimte met een opgefrommeld vloerkleed.


Dat is een driedimensionale structuur, maar als je beter kijkt zie je dat het om een tweedimensionaal kleed gaat, en pak je er een loep bij, dan blijkt het hele kleed geweven te zijn van één enkele eendimensionale draad.


‘Op de allergrootste schaal, vergelijkbaar met de afmetingen van het waarneembare heelal, zou onze driedimensionale ruimte ook weer geplooid en gevouwen kunnen zijn tot een vierdimensionaal geheel,’ aldus Landsberg.


Of er op nóg grotere schaal zelfs sprake kan zijn van een vijfde dimensie, durft hij niet te zeggen. ‘Alles is mogelijk.’


Maar daar zit ’m nou net de kneep, volgens de criticasters – alles lijkt maar te kunnen.

‘Ik neem een exotisch idee alleen serieus als er meetbare consequenties uit tevoorschijn komen,’ zegt Icke, ‘of als er fundamentele problemen mee verklaard worden.


Veel andere dingen dragen weinig of niets bij, of kunnen zelfs nooit door waarnemingen en experimenten worden onderbouwd of weerlegd.


Dan is zo’n theorie volslagen gratuit.’ Ook snaar-theoreticus Robbert Dijkgraaf van de Universiteit van Amsterdam is bepaald niet onder de indruk: ‘Het theoretische en experimentele laagje ijs waarop Landsberg en zijn collega’s schaatsen is erg dun.’


’t Hooft is bij nader inzien toch net iets milder. ‘Deze mensen weten in ieder geval waar ze over praten, en zien dus zelf de moeilijkheden ook wel in,’ zegt hij.


‘Maar ik vind de prijs die je betaalt voor deze theorie nogal hoog: allerlei waardevolle concepten lijken te sneuvelen, en er komt weinig bruikbaars voor in de plaats.’


Bovendien, aldus ’t Hooft, moet alles wel ‘streng logisch in elkaar zitten, en dat heb ik nog niet gezien.’ Overigens werkt hij zelf ook aan een ‘wild idee’ dat conforme gravitatie heet. ‘Maar dat is verre van uitgewerkt en nog niet wetenschappelijk onderbouwd.’


Landsberg blijft voorlopig onverminderd enthousiast. Als de driedimensionale ruimte op de grootste schaal gevouwen en geplooid is, kan een ander deel van het heelal zich vlak bij het onze bevinden, op zeer kleine afstand in de vierde dimensie.


Tussen die ‘naburige’ delen kunnen dan quantumeffecten optreden die een beetje vergelijkbaar zijn met het beroemde Casimir-effect.


Dat zou mogelijk een verklaring kunnen opleveren voor de onbegrepen donkere energie, die tot de versnellende uitdijing van het heelal leidt. ‘Maar daar moeten inderdaad nog realistische wiskundige modellen voor worden uitgewerkt,’ geeft hij toe.




En wat als er op microscopische schaal inderdaad dimensies verdwijnen?


‘Dan gaan we dat misschien zien in botsingsexperimenten in de LHC-versneller van CERN,’ zegt Landsberg, die zelf aan een van de CERN-experimenten meewerkt.


‘Je verwacht dan dat de deeltjes die bij een extreem energierijke botsing geproduceerd worden voornamelijk in één vlak bewegen.


Voorzichtige aanwijzingen daarvoor blijken een jaar of tien geleden al eens te zijn waargenomen, maar die resultaten brachten het toen niet verder dan een vrij obscuur Russisch tijdschrift, waardoor ze nooit veel aandacht hebben gekregen.’


‘Natuurlijk kun je theoretici niet verbieden met vergezochte ideeën te komen,’ zegt Vincent Icke.

‘Het verbieden van een theorie komt altijd van waarnemingen en experimenten. De natuur zal wel uitmaken wat mag en wat niet.’


Maar, verzucht hij, als de LHC-metingen niets te zien geven, kunnen Landsberg en zijn collega’s zich altijd verschuilen achter de conclusie dat de effecten dan misschien pas bij een nóg veel hogere energie optreden.


‘In het Engels heet dat weaseling out. Dat vind ik het glibberige eraan. Ik houd meer van mouwen opstropen en rekenen.


Houd je eerst maar eens bezig met de dingen die wél meetbaar zijn.’


Robbert Dijkgraaf ziet veel meer in de snaartheorie als route naar een oplossing voor de crisis in de deeltjesfysica en de kosmologie.


‘Op kleine lengteschalen vervagen onze klassieke ideeën over ruimte en dimensie misschien wel, en moeten ze worden vervangen door quantumbegrippen,’ zegt hij.


Maar Gerard ’t Hooft loopt ook daar niet warm voor: ‘Stephen Hawking moet zelf weten waar hij zijn geld op zet, maar de snaartheorie komt vaak ook met flutverklaringen.’


Zo lang er nog zo veel onenigheid is over de betekenis van een ‘gevestigd’ idee als de snaartheorie, kun je het creatieve natuurkundigen als Greg Landsberg misschien niet kwalijk nemen dat ze plezier beleven aan het speculeren over verdwijnende dimensies.


'Misschien was er héél kort na de geboorte van het heelal wel sprake van slechts één ruimtelijke dimensie en één tijddimensie,’ filosofeert hij er dan ook vrolijk op los. ‘Wie weet komen we er op deze manier ooit nog eens achter waarom je in de ruimte wél alle kanten op kunt, terwijl de tijd maar één richting heeft.’


© Govert Schilling








Phantom Universe - Next Biggest Mystery

Analysis by Ray Villard


Mon Aug 16, 2010 04:27 PM ET




It’s sort of the "Academy Awards" for deep space astronomy, except it only happens once every 10 years.

Last Friday a blue-ribbon National Academy of Sciences (NAS) committee released its recommendations for what types of telescopes astronomers should be building over the next decade.


This offers to Congress, NASA and the National Science Foundation an exploration roadmap sanctioned by our nation’s top researchers.

My colleague Nicole Gugliucci has a nice overview of the report's winners and runner-ups.


What’s fascinating is that a decade ago, it would have been hard to predict what would have made it to the top of the list of cosmic mysteries now confronting astronomers.


In the 2001 NAS Decadal Survey report, the big questions were about the age, history and expansion of the universe; understanding the formation and evolution of black holes of all sizes; studying the formation of stars and their planetary systems; and understanding how the astronomical environment affects Earth. Significant inroads were made into some of these areas, or are awaiting pursuit by telescopes now under construction.


Taking a closer look at the top science goals for the upcoming decade, it seems that the fundamental physics of the universe takes center stage.




The top-ranked space mission, called the Wide Field Infrared Survey Telescope (WFIRST), would use three types of observations to characterize dark energy.


Dark energy, an unimaginably weak energy field from the vacuum of space, is pushing the universe apart at an ever-faster rate.


This “dark force” is so far from what would have been predicted that Mike Turner of the University of Chicago calls it “the most embarrassing number in physics.” Therefore, it arguably is the most perplexing phenomenon ever to confront modern science.


As monumentally profound as this mystery is, I find it dissatisfying.


Scientists are delighted at putting ever-tighter error bars around their observations. 


If built and launched for an estimated $1.5 billion, WFIRST will help physicists eliminate some theories for dark energy.


We’ll know what dark energy isn’t. But the resulting dataset might never explain exactly what dark energy is.

Turner has even confessed that we simply may never know.


WFIRST will also look for Earth-like planets in the far reaches of the galaxy using a technique called microlensing.

This will build up the knowledge base for the abundance of Earth-sized planets in space. But, again, it’s just statistics and error bars.


I also find this dissatisfying because the newfound planets won’t be close enough to us for follow-on observations to see if they have habitable conditions.


Such a telescope will not take us any closer to answering the “L” world: Life in space.


The mega-space telescopes needed for that task won’t be technologically ready for at least another decade, and the 2020 NAS survey report.


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A brave new frontier that could burst open by the end of the decade is the ghostly realm of gravity waves. Spacetime should be ringing like a bell as black holes collide and supernova cores implode.


Though gravity waves have not yet been detected in ground-based experiments,

the NAS highly ranked the Laser Interferometer Space Antenna (LISA) because it would open up a whole new discovery space by detecting these whispers from massive objects gone wild.


But it will need a technological demonstrator precursor mission before anyone is willing to pony up approximately $3 billion for LISA.


Planned for 2012 is the European Space Agency’s  LISA Pathfinder mission that will test a series of ultra-high precision technologies on a small single spacecraft.


The front-runner in recommended new ground-based telescopes is the Large Synoptic Survey Telescope LSST



Large Synoptic Survey Telescope.jpg


(which also was on the to-do list in the last Decadal Survey). This machine is truly astronomical in every sense of the word.

It will essentially survey the entire sky on a weekly basis.


For the first time ever astronomers will have a time-lapse color movie of the universe.


It will capture wayward asteroids and comets, erupting stars, and anything else that moves or flashes in the night.


Untold wonders await. The resulting 1,000-terabyte data archive will be a “treasure trove,” the NAS report predicts.

Ranked lower on the space observatory list, and a disappointment to the aspirations of high-energy astrophysicists,

is the proposed $5 billion International X-Ray Observatory (IXO). Previously called Constellation-X,


it ranked higher than the LSST in the last Decadal Survey. The IXO would probe gravity in the extreme, as it behaves around distant black holes.

The IXO would also offer unique observational tests of dark energy and dark matter.


X-Ray astronomy has had a bumpy history. The first space observatory, Uhuru, opened up the X-ray universe in 1970.


A series of high-energy observatories followed in the late 1970s.


But X-ray astronomers had to wait another 20 years for the prolific Chandra X-Ray Observatory to come along.

But a member of the 2010 Decadal Survey stated that IXO had a “limited potential for great discoveries.” Ouch!


Based on this history, what will the next Decadal Survey rank in 2020?


I expect that by then the upcoming James Webb Space Telescope will fill in the opening chapter of the birth of stars and galaxies, by taking us back to within 200 million years of the Big Bang. But, given the fast pace of discoveries in exoplanets,


I think the overarching quest will be for finding habitable worlds.


I’m also sure that facilities like LSST will uncover remarkable new phenomena that need follow-up observations.













Nieuw techniek ontwikkeld voor onderzoek donkere energie !

dark energy cygnus.jpg
21 juli 2010

National Radio Astronomy Observatory 
Radiosterrenkundigen hebben een nieuwe techniek ontwikkeld om grote kosmische structuren in kaart te brengen.
Met deze techniek hopen zij meer te weten komen over de geheimzinnige 'donkere energie' in het heelal (Nature, 22 juli).

'Donkere energie' is de naam die sterrenkundigen hebben gegeven aan de nog onbegrepen oorzaak van de versnellende uitdijing van het heelal.
Er zijn verschillende theorieën bedacht om die versnellende uitdijing te verklaren, maar tot nog toe is het niet gelukt om de verschillende kandidaten te

De sleutel wordt gezocht bij metingen van de grootschalige verdeling van sterrenstelsels in het heelal.

Het meten van de afstanden en snelheden van vele miljoenen sterrenstelsels is een tijdrovende klus.

Bij de nieuwe techniek, die intensity mapping wordt genoemd, wordt echter niet naar afzonderlijke sterrenstelsels gekeken,
maar naar de radiostraling die afkomstig is van neutraal waterstofgas uit een groot gebied dat grote aantallen stelsels omvat.

Op die manier wordt een flink stuk heelal in één keer gemeten en kan veel sneller inzicht worden verkregen in de wijze waarop grote kosmische structuren
zich de afgelopen miljarden jaren hebben ontwikkeld.

En met die informatie kan dan weer de 'beste' theorie voor de verklaring van de donkere energie worden geselecteerd.
© Eddy Echternach (www.astronieuws.nl)
URL van deze pagina:

Radio Astronomers Develop New Technique for Studying Dark Energy


X-ray Discovery Points to Location of Missing Matter

Scientists using two X-ray telescopes (Chandra and XMM-Newton) have found evidence for the "missing matter" in the nearby Universe. This matter is made up of hot diffuse gas, which is known as WHIM (warm-hot intergalactic medium). To get this result, researchers analyzed X-ray light from a distant quasar that passed through a "wall" of galaxies about 400 million light years from Earth.Scientists have used NASA's Chandra X-ray Observatory and ESA's XMM-Newton to detect a vast reservoir of gas lying along a wall-shaped structure of galaxiesabout 400 million light years from Earth. In this artist's impression, a close-up view of the so-called Sculptor Wall is depicted. Spiral and elliptical galaxies are shown in the wall along with the newly detected intergalactic gas, part of the so-called Warm Hot Intergalactic Medium (WHIM), shown in blue. This discovery is the strongest evidence yet that the "missing matter" in the nearby Universe is located in an enormous web of hot, diffuse gas.The X-ray emission from WHIM in this wall is too faint to be detected, so instead a search was made for absorption of light from a bright background source by the WHIM, using deep observations with Chandra and XMM. This background source is a rapidly growing supermassive black hole located far beyond the wall at a distance of about two billion light years. This is shown in the illustration as a star-like source, with light traveling through the Sculptor Wall towards the Earth. The relative location of the background source, the Sculptor Wall, and the Milky Way galaxy are shown in a separate plot, where the view instead looks down on the source and the Wall from above.An X-ray spectrum of the background source is given in the inset, where the yellow points show the Chandra data and the red line shows the best model for the spectrum after including all of the Chandra and XMM data. The dip in X-rays towards the right side of the spectrum corresponds to absorption by oxygen atoms in the WHIM contained in the Sculptor Wall.The characteristics of the absorption are consistent with the distance of the Sculptor Wall as well as the predicted temperature and density of the WHIM.This result gives scientists confidence that the WHIM will also be found in other large-scale structures.This result supports predictions that about half of the normal matter in the local Universe is found in a web of hot, diffuse gas composed of the WHIM. Normal matter — which is different from dark matter -- is composed of the particles, such as protons and electrons, that are found on the Earth, in stars, gas, and so on. A variety of measurements have provided a good estimate of the amount of this "normal matter" present when the Universe was only a few billion years old. However, an inventory of the nearby Universe has turned up only about half as much normal matter, an embarrassingly large shortfall.COPYRIGHT : Chandra X Ray telescope URLhttp://chandra.harvard.edu/photo/2010/h2356/chandra


Donkere materie in kaart gebracht

26 april 2010Subaru Telescope Een internationaal team van sterrenkundigen heeft voor het eerst de verdeling van donkere materie in clusters van sterrenstelsels duidelijk in kaart gebracht. Uit hun onderzoek blijkt dat deze verdeling eerder de vorm van een rugbybal heeft dan die van een voetbal. En dat is precies wat op theoretische gronden werd verwacht. Bij het opsporen van de donkere materie, die zoals de naam als suggereert niet rechtstreeks waarneembaar is, is gebruik gemaakt van het zogeheten gravitatielenseffect. Dat effect is het gevolg van de licht-afbuigende werking van materie. Door heel nauwkeurig te onderzoeken hoe sterk een verre cluster van sterrenstelsels het licht van nog verder weg gelegen objecten afbuigt, kan worden vastgesteld hoe de materie in zo'n cluster is verdeeld. Op die manier hebben Japanse, Taiwanese en Britse sterrenkundigen met de Subaru-telescoop op Hawaï twintig clusters onderzocht. Daarbij is gebleken dat de verdeling van de donkere materie de vorm heeft van een afgeplatte bol. En dat is in overeenstemming met de heersende gedachte dat donkere materie uit zogeheten WIMP's bestaat: traag bewegende, zware deeltjes die een overblijfsel zijn van de oerknal. © Eddy Echternach (www.astronieuws.nl)COPYRIGHT ALLES OVER STERRENKUNDE EN SUBARU TELESCOPE !!URL http://allesoversterrenkunde.nl/nieuws/3918-Donkere-materie-in-kaart-gebracht.htmlURL SUBARU TELESCOPEhttp://www.subarutelescope.org/Pressrelease/2010/04/26/index.htmlfeat_beyondgalileo_diag_zoom


Lightening the dark

About 96% of the Universe is in the form of unknown matter and energy. The rest – only 4% – is the ‘ordinary matter’ that we are made of and that makes up all the planets, the stars and the galaxies we observe. The LHC experiments have the potential to discover new particles that could make up a large fraction of the Universe.In recent years, scientists have collected various evidence of the existence of a new type of matter in the Universe. They call it ‘dark’ because it does not emit or absorb electromagnetic radiation. "One of the main proofs of its existence comes from the measurement of the rotational speed of astronomical bodies in spiral galaxies", explains Gian Giudice, a member of CERN's Theory group and the author of "A Zeptospace Odyssey", a recent book on LHC physics aimed at the general public.According to the Newtonian laws of motion, this value varies as a function of the distance from the centre of the galaxy: more distant objects should rotate at a lower speed than those situated nearer the centre. However, back in the 1970s, astronomers found that outer stars move at a higher rotational speed than expected. “With such a velocity, the attractive gravitational force exerted by the observable mass would not be enough to keep those stars in the galaxy,and stars would simply escape”, continues Gian Giudice. Therefore, something must exist that keeps the galaxy together by exerting gravitational attraction."The second strong piece of evidence suggesting the existence of dark matter comes from the 'gravitational lensing' effect, in which galactic clusters bend the light coming from more distant objects. The way the light is deviated shows that the total mass contained in the clusters must be much larger than what we observe”, explains Giudice. Moreover, studies on the way in which the initial atoms and molecules formed in the Universe show that ordinary matter cannot account for more than 4% of the Universe. This fact allows scientists to exclude the possibility that invisible matter is made of massive objects such as Jupiter-sized planets. On the other hand, theory and observations do not exclude that dark matter is made of primordial black holes in which large amounts of matter could be trapped. However, this latter possibility seems very remote, and scientists tend to think that dark matter is made of a new type of particle.How could the LHC help enlighten physicists?"The yet undiscovered dark matter has to meet some requirements imposed by observations and theory", says Gian Giudice. "It has to be stable, it has to carry no charge, and it has to be relatively heavy”.Through studies on the evolution of the Universe, scientists have been able to infer the mass of the dark matter constituents, situating it between 100 GeV and 1 TeV (for reference, the mass of the proton is about 1 GeV). Interestingly enough, this is exactly the same mass range in which theories beyond the Standard Model anticipate the existence of new particles.“The LHC will explore exactly that range of energies. Therefore, if new particles exist, the LHC has a big chance of finding them”, confirms Gian Giudice. He adds: “The theoretical supersymmetric model suggests three possible candidates for dark matter: the neutralino, the gravitino and the sneutrino. However, it is important to note that supersymmetry is not the only possible scenario".Besides the whole plethora of possible alternative scenarios, even if the LHC experiments find evidence of new particles, it will not be possible to claim that they are the actual components of dark matter. For this, confirmation will be needed from other dedicated experiments.From deep inside the Earth to outer spaceOther experiments are searching for the elusive dark matter particles. Some of them, such as the CDMS experiment at the Soudan Underground Laboratory in Minnesota, and the XENON and DAMA experiments at the Gran Sasso Laboratory in Italy, are installed underground. Others, such as Pamela and Fermi (also at Gran Sasso), are in orbit around our planet.by Francesco PoppiCopyright CERN 2010 - CERN Publications, DG-COhttp://cdsweb.cern.ch/journal/CERNBulletin/2010/18/News%20Articles/1261775?ln=enbild_LHC_Cern


Cosmic Dark Matter Clumps Into Cigar Shapes

By Clara MoskowitzSPACE.com Senior Writerposted: 26 April 201003:09 pm ETElusive dark matter around clusters of galaxies often clumps into cigar shapes, new observations show.The discovery could help scientists finally understand what makes up dark matter, which is the mystifying stuff thought to exist invisibly all around us. Dark matter, which could be more than five times more abundant than visible matter, is only detectable through its gravitational pull on regular material.According to the new observations, the dark matter around many galaxy clusters is a flattened, cigar-like shape, rather than a rounded sphere."There are clear theoretical predictions that we expect dark mater haloes to be flattened like this," said study co-author Graham P. Smith of the U.K.'s University of Birmingham. "It's a very beautiful, very clean and direct measurement of that."Smith and the team, led by Masamune Oguri of the National Astronomical Observatory of Japan and Masahiro Takada at the University of Tokyo, used a quirk of gravity called gravitational lensing to observe dark matter's gravitational effects on large collections of galaxies known as galaxy clusters. Gravitational lensing occurs when mass warps space-time, causing light to travel along a curved path when it passes by. The amount of curving can tell astronomers how massive celestial objects are.For this study, the researchers used the Prime Focus Camera on the Subaru Telescope on Mauna Kea in Hawaii to observe 20 galaxy clusters. They took advantage of gravitational lensing to create maps of the distribution of mass around the clusters, thus getting a peek into the secrets of dark matter."What we're probing with these gravitational lensing observations is the dark matter distribution, because the dark matter dominates the mass on these large scales," Smith told SPACE.com.The fact that the dark matter seems to be flattened out into oblong shapes fits in with the so-called cold dark matter theory. Computer simulations based on this theory have predicted such shapes, but they have never before been verified to such an extent with so many large clusters.The findings could shed light on the fundamental nature of this weird stuff, which scientists cannot detect directly. The observations support the possibility that dark matter is actually made of tiny particles called WIMPS (weakly-interacting massive particles) that exert a strong gravitational force, but otherwise don't interact with normal matter.The research will be detailed in the Monthly Notices of the Royal Astronomical Society.Copyright SPACE.comhttp://www.SPACE.com/scienceastronomy/dark-matter-galaxy-clusters-100426.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+spaceheadlines+%28SPACE.com+Headline+Feed%29&utm_content=Google+Reader080923-galaxy-cluster-02





IceCube is één van de experimenten die zoekt onder andere naar neutrinosignalen van donkere materiedeeltjes in het heelal.

Het heelal bevat volgens de huidige inzichten van het wetenschappelijk onderzoek zo'n 4 procent gewone materie, daarnaast ongeveer 26 procent donkere materie, de overige 70 proageztextmedcent zou staan voor donkere energie. Eén van de projecten om de ware aard van de donkere materie te achterhalen is IceCube. Het IceCube project wordt uitgevoerd door een internatio¬naal consortium van 30 universiteiten uit de USA, Europa, Japan en Nieuw-Zeeland. IceCube is de grootste neutrinodetector ter wereld en bevindt zich nabij de Amundsen Scott Zuid poolbasis. De detector bestaat uit een rooster van 4800 lichtgevoelige sensoren die gespreid zijn over een volume van een kubieke kilometer en begraven zitten in het ijs op 1450 tot 2450 meter diepte. De missie van IceCube is de observatie van neutrino's uit de ruimte, afkomstig van actieve sterrenstelsels, Gamma Ray Bursts, donkere materie, supernovae, en dergelijke meer.



For many years, the absence of antimatter in the Universe has tantalised particle physicists and cosmologists: while the Big Bang should have created equal amounts of matter and antimatter, we do not observe any primordial antimatter today. Where has it gone? The LHC experiments have the potential to unveil natural processes that could hold the key to solving this paradox. Every time that matter is created from pure energy, equal amounts of particles and antiparticles are generated. Conversely, when matter and antimatter meet, they annihilate and produce light. Antimatter is produced routinely when cosmic rays hit the Earth's atmosphere, and the annihilations of matter and antimatter are observed during physics experiments in particle accelerators. If the Universe contained antimatter regions, we would be able to observe intense fluxes of photons at the boundaries of the matter/antimatter regions. “Experiments measuring the diffuse gamma-ray background in the Universe would be able to observe these light emissions”, confirms Antonio Riotto of CERN's Theory group. “In the absence of such evidence, we can conclude that matter domains are at least the size of the entire visible Universe”, he adds. What caused the disappearance of antimatter in favour of matter? “In 1967, the Russian physicist Andrej Sakharov pointed out that forces discriminating between matter and antimatter, called “CP-violating” effects, could have modified the initial matter-antimatter symmetry when deviations from the thermal equilibrium of the Universe occured”, says Antonio Riotto. In the cold Universe today, we can only observe very rare CP-violating effects in which Nature prefers the creation of matter over antimatter. Following their discovery in the decays of K-mesons containing strange quarks, they have now also been observed in the decays of B mesons, which contain bottom quarks. Today, scientists think that the early Universe might have gone through a transition phase in which the thermodynamic equilibrium was broken, when the density of the Universe was very high and the average temperature was one billion or more times that inside the Sun. "Some physicists think that this might have happened through the formation of ‘bubbles’ which have progressively expanded, thus ‘imposing’ their new equilibrium on the whole pre-existent Universe", explains Antonio Riotto. Whatever the real dynamics of this phase actually were, the important thing is that one particle of matter in every 10 billion survived, while all the others annihilated with the corresponding antiparticles. How can the LHC help to solve the mystery? By studying rare decays, experiments can bring us more accurate information about phenomena related to CP-violation involving both known and new particles, such as mesons containing both bottom and strange quarks. Moreover, if new supersymmetric particles are discovered at the LHC, some of the possible scenarios leading to a non-equilibrium phase could find experimental support. "If the LHC finds a Higgs boson with a mass less than about 130 GeV, and if this discovery comes with the detection of a light supersymmetric particle called ‘stop‘, this could be the experimental proof that the non-equilibrium phase happened through the formation of bubbles", concludes Antonio Riotto. In any case, since the disappearance of primordial antimatter cannot be explained by the current Standard Model theory, it is clear that we have to look for something new. Scientists are exploring different avenues but, given the fact that what we observe represents only about 4% of the total energy and matter that the Universe is made of, one can guess that part of the key to solving the antimatter mystery could be held in the yet unknown part of the Universe. With its very high discovery potential, the LHC will certainly help shed light on the whole issue.antimatterCOPYRIGHT CERN BULLETIN URL :http://cdsweb.cern.ch/journal/CERNBulletin/2010/16/News%20Articles/1255394?ln=en


Distant Galaxies Unlock New Secrets of Dark Matter

dark matterTo weigh the universe, scientists use two kinds of cosmic scales: one to measure all the regular matter out there, and another to deduce how much invisible dark matter remains hidden underneath.These calculations have been taken further than ever before by a new study that tallied both types of mass in smaller and more distant groups of galaxies than any previous projects. The project found that these faraway galactic clusters have roughly the same proportion of dark matter to regular matter as the closer galaxy groups do.The findings could help astronomers understand more about dark matter, as well as its even stranger sibling – dark energy.Invisible universeDark matter is a form of stuff that does not interact with light, so cannot be seen, but makes its presence felt by exerting a gravitational pull on normal matter.Astronomers measure how much dark matter lies in galaxies by a fluke of physics called gravitational lensing. This phenomenon, predicted by Einstein's theory of general relativity, causes light to curve as it flies through space-time that has been dented by the gravity of large bodies of mass. For example, groups of massive galaxies will gravitationally warp the space-time around them, forcing light to bend as it passes through, and causing them to look distorted when their light reaches our telescopes. Scientists can tell how much total mass there is by how much of this distortion occurs.Next, researchers calculate how much normal matter is in a cluster of galaxies by looking at its X-ray light, since the light must be coming from only the regular stars and gas that make up the cluster.Comparing these two calculations — the total matter to just the regular matter — gives a ratio astronomers call the mass-luminosity relation. So far, the mass-luminosity relation has been measured well for nearby, large galaxy clusters, but there has not been good enough X-ray data to probe farther or smaller, dimmer clusters of galaxies."We can map out the big cities, but no one's been able to map out the villages yet," said Alexie Leauthaud of the Lawrence Berkeley National Laboratory in Berkeley, Calif., leader of the new study.New rangesAstronomers used observations from the European Space Agency's XMM-Newton satellite and from NASA's Chandra satellite, as well as data from the Hubble Space Telescope's Cosmic Evolution Survey (COSMOS). These ultra-high resolution photos allowed the scientists to extend the mass-luminosity relation further than ever before.With such dim objects, the gravitational lensing wasn't immediately apparent. So researchers used a statistical analysis to measure the orientation and shape of the galaxies to find small distortions due to so-called weak lensing.They found that the same general ratio of dark matter to normal matter prevailed in these distant, small clusters as for nearby, larger clusters."We didn't know what to expect going down to lower masses or [farther distances], and we find this nice simple relationship," Leauthaud told SPACE.com. "Now the aim is to find out why we find this nice, simple relationship."Dark energy enigmaThe finding may help shed light on an even more bizarre aspect of the universe — dark energy. Dark energy is the name given to whatever mysterious force is causing the universe to accelerate as it expands."We want to try to understand the properties of dark energy," Leauthaud said. "One way to measure properties of dark energy is to measure the number of structures that have formed for a given amount of dark matter."Dark energy basically works against gravity in a tug-of-war. While gravity constantly pulls mass inward, encouraging things to clump together and condense into smaller space, dark energy does the opposite. This force somehow pulls everything apart, causing everything in the universe to move away from everything else at ever-increasing speeds.When mass clumps together enough to form galaxies, it means that gravity has won on those scales, helping things to stick together despite the pull of dark energy. So the more astronomers can measure when and how structures formed in the universe, the better they can understand just how far dark energy's pull reaches.Copyright http://www.space.com/scienceastronomy/dark-matter-galaxy-clusters-100126.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+spaceheadlines+%28SPACE.com+Headline+Feed%29&utm_content=Google+Reader



Onze tijd is begonnen met de oerknal. De tijd erover extrapoleren, is niet evident.Zoals 'ten noorden van de noordpool' niet bestaat, is iets als 'voor de oerknal' ook niet zomaar zinvol.We kunnen erover speculeren, in de zin dat ruimte en tijd in mathematische concepten kunnen gegoten worden, en de wiskunde laat vele varianten toe. Maar in termen van fysisch experimenteren, en dus soliede kennis opbouwen, is de oerknal een grens waar we moeilijk overheen geraken: naarmate we dichter bij de oerknal komen, stijgen dichtheid, druk, temperatuur, maar ook onze onwetendheid. In de oerknal worden ze alle - ook onze onwetendheid dus - oneindig. En voorbij oneindig kan je niet extrapoleren... Besef aub dat wij product zijn van het heelal. Wij, dat zijn de atomen waaruit wij bestaan, maar ook de concepten die we hanteren, inclusief ruimte en tijd. Spreken over die concepten als voorafgaande voorwaarde voor het heelal, is een stap te ver.Deze vraag werd beantwoord door:Prof. Christoffel Waelkens Gewoon Hoogleraar SterrenkundebigbangCopyright : http://ikhebeenvraag.be/vraag/6749


Neutrino May Have Triggered Dark Energy 28122008

CompositionCosmos_550CompositionCosmos_550A new theory may explain the mysterious force that is causing our universe to expand at a faster and faster rate. By Irene Klotz | Mon Dec 28, 2009 10:05 AM ET Seventy-five percent of the universe's mass and/or energy must be comprised of dark energy to explain the universe's observed rate of acceleration.NASA/CXC/UCLA/M. Muno et al.Could a neutrino -- an electrically neutral and nearly mass-free sibling to the electron -- have triggered dark energy, the anti-gravity force discovered just over a decade ago?That's the latest idea from a team of theoretical physicists who suggest that dark energy was created from neutrino condensate in the split second after the universe's birth 13.7 billion years ago.The idea sprang from calculations showing that the density of dark energy is comparable to the value of neutrino mass, said lead researcher Jitesh Bhatt, with the Physical Research Laboratory in Ahmedabad, India.Dark energy, an unknown force that is accelerating the expansion of the universe, is the leading cosmological mystery of modern-day science.It was discovered in 1998 after astrophysicists noted that supernovae -- the exploded remains of massive stars -- showed an accelerated rate of expansion in the last 2 billion years or so when compared to older epochs. Explanations for dark energy fall into two basic camps: those theories that add a new physical entity or those that change the laws of gravity, said Eric Linder with the University of California at Berkeley."If you search for 'dark energy' in just the titles (of research papers) in the past year, you will find 200 speculations on what dark energy is," Linder wrote in an email to Discovery News. "There are a great many hypotheses for dark energy. Some ties to neutrinos have been considered for the last several years, but nothing substantial has yet come out of them."To account for the universe's observed rate of acceleration, 75 percent of the mass and/or energy of the universe has to be comprised of a gravitationally repulsive force, or dark energy.Scientists are developing several dark energy experiments, including the NASA/Department of Energy Joint Dark Energy Mission, in an attempt to refine dark energy measurements and reveal how it operates."It will take much more work before we can pin down the nature of dark energy," Bhatt said. "Without knowing the nature of the dark energy, our knowledge of theoretical physics would remain incomplete."Bhatt's research was published in last month's issue of Physical Review D.copyright http://news.discovery.com/videos/space-study-sheds-light-on-dark-energy.htmlCompositionCosmos_550


Mystery Swirls Around 'Dark Stars'

By Charles Q. ChoiSPECIAL to SPACE.composted: 21 December 200908:21 am ETWhen the very first stars lit up, they may have been fueled by the dark matter that has long eluded scientists.These "dark stars," first born nearly 13 billion years ago, might still exist today. Although they would not shed any visible light, astronomers might detect these invisible giants — some 400 to 200,000 times wider than our sun and 500 to 1,000 times more massive — because they should spew gamma rays, neutrinos and antimatter and be linked with clouds of cold, molecular hydrogen gas that normally would not harbor such energetic particles.If scientists find these stars, they could aid the search to discover and identify dark matter. They could also help solve the mystery of why black holes formed much faster than expected.Scientists think unseen, as-yet unidentified dark matter makes up about 95 percent of all matter in the universe. They know it exists because galaxies rotate faster than can be explained by the visible matter within them. Among the main candidates for what dark matter is are WIMPs, or weakly interacting massive particles. One type of WIMP that scientists theorize exists is called a neutralino. These particle can annihilate each other, generating heat. They would also produce quarks and their antimatter counterparts, antiquarks, which would collide to emit gamma rays, neutrinos and antimatter such as positrons and antiprotons.The researchers calculated that in the newborn universe, some 80 to 100 million years after the Big Bang, as proto-stellar clouds of hydrogen and helium tried to cool and shrink, annihilating neutralinos would have kept them hot and large. The result might be dark stars, fueled by dark matter instead of nuclear energy as in normal stars. These would have been made up largely of normal matter, mostly in the form of hydrogen and helium, but would be vastly larger and fluffier than the sun and current stars."It's a completely new type of star with a new power source," said researcher Katherine Freese, a theoretical physicist at the University of Michigan.Originally researcher Paolo Gondolo, a particle astrophysicist at the University of Utah, wanted to dub these new, theoretical kinds of invisible stars "brown giants," similar to dim but smaller, Jupiter-sized stars known as "brown dwarfs." But he said his collaborators insisted on calling them "dark stars," after the song "Dark Star" first played in 1967 by the revered rock band The Grateful Dead. "There is a dark star song by Crosby, Stills, Nash and Young, too, that we had in mind," Freese said."It was a good name," Gondolo noted. Although dark stars are made up  of less than 1 percent dark matter, "it's very important," he explained. "It converts all of its mass to energy with 100 percent efficiency, under Einstein's equation, E=mc2. Normal stars that rely on nuclear energy convert just a small fraction of its mass to energy, 1 or 2 percent."There was initially skepticism as to whether dark matter densities were high enough in the early universe to support the creation of dark stars. "However, we've checked it and so have two other groups, and they agree with us," Freese said. Dark stars could be detected with the next-generation James Webb Space Telescope currently scheduled for launch in 2014. "It may be that these stars eventually cluster together, and clusters of them might be visible with the James Webb Space Telescope," Gondolo said.If scientists do discover dark stars, "they would tell us a very important thing — that dark matter is made of elementary particles," Gondolo said. "At this moment, we know absolutely nothing about what dark matter is made of. We know where dark matter is, how much is there, but we don't know its nature."Dark stars might also explain why black holes formed much faster than expected. Astronomers have found black holes that existed only a few hundred million years after the Big Bang, yet current theories suggest they should have taken longer to form. Dark stars might have collapsed into black holes very early, Gondolo said, because they might be very short-lived and could have formed when the universe was young.In addition, dark stars could solve a puzzle seen with stars in the galactic halo, the murky, roughly spherical part of the galaxy extending past the main, visible component. "There's an abundance of elements in the very old halo stars that's hard to explain, and dark stars can explain that — they would end up creating the chemical abundances needed," Gondolo said.It is unlikely any dark stars are being formed today, Freese said."The early universe was more compact than it is now, and everything was denser, including the amount of dark matter one had at any one place," she explained. "Now the universe has expanded and things are less dense, making it harder to make dark stars today."It remains uncertain just how long dark stars might live, Freese said."The ones that formed in the early universe could have continued as long as they had dark matter to power them," Freese said. "They start at the center of dark matter 'halos' — giant spherical globes of dark matter — and these are always merging with other ones, so some might have burned out their dark matter fuel very early and become either normal stars or collapsed, but it remains an open question if any have survived until now."copyright : Space,com http://www.space.com/scienceastronomy/091221-mm-dark-stars.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+spaceheadlines+%28SPACE.com+Headline+Feed%29&utm_content=Google+ReaderDark Star


Nieuwe zoektocht naar donkere energie van start gegaan

In de nacht van 14 op 15 september is de Baryon Oscillation Spectroscopic Survey (BOSS) van start gegaan. Deze hemelverkenning heeft tot doel om de geschiedenis van de uitdijing van het heelal in kaart te brengen. BOSS maakt gebruik van een verschijnsel dat baryon-akoestische oscillaties wordt genoemd. Deze oscillaties zijn begonnen als drukgolven in het hete plasma van het jonge heelal, die zich aanvankelijk met grote snelheid door het heelal voortplantten. Maar toen het heelal een paar honderdduizend jaar oud was, was het zo sterk afgekoeld dat de golven tot stilstand kwamen. Het restant van deze 'bevroren' golven heeft zijn sporen achtergelaten in de ruimtelijke verdeling van sterrenstelsels. Door de afmetingen van de baryon-akoestische oscillaties te meten, kan worden vastgesteld hoe de donkere energie de uitdijing van ons heelal in de loop der tijden heeft beïnvloed. Daartoe zal BOSS de afstanden (of beter gezegd: roodverschuivingen) van 1,4 miljoen sterrenstelsels en 160.000 quasars meten - objecten die zich op afstanden van 7 tot 11 miljard lichtjaar bevinden. Ook worden de dichtheidsverschillen in het gas tussen de stelsels gemeten. Dat gebeurt met een spectrograaf waarvoor meer dan 2000 metalen platen zijn gemaakt, waarin een duizendtal kleine gaatjes zitten. Deze platen worden in het brandpunt van een 2,5-meter telescoop geplaatst. Een computergestuurd systeem prikt glasvezels in de gaatjes, zodat in één keer de spectra van een groot aantal sterrenstelsels kunnen worden opgenomen. Het waarnemingsprogramma, waaraan 160 wetenschappers van 42 instituten deelnemen, gaat vijf jaar duren. De eerste resultaten worden eind 2010 verwacht. Copyright : http://allesoversterrenkunde.nl/nieuws/3503-Nieuwe-zoektocht-naar-donkere-energie-van-start-gegaan.html© Eddy Echternach (www.astronieuws.nl)Copyright : http://newscenter.lbl.gov/press-releases/2009/10/01/first-light-boss/dark energy


Astronomers Closing in on Dark Energy with Refined Hubble Constant

The name “dark energy” is just a placeholder for the force — whatever it is — that is causing the Universe to expand. But astronomers are perhaps getting closer to understanding this force. New observations of several Cepheid variable stars by the Hubble Space Telescope has refined the measurement of the Universe’s present expansion rate to a precision where the error is smaller than five percent. The new value for the expansion rate, known as the Hubble constant, or H0 (after Edwin Hubble who first measured the expansion of the universe nearly a century ago), is 74.2 kilometers per second per megaparsec (error margin of ± 3.6). The results agree closely with an earlier measurement gleaned from Hubble of 72 ± 8 km/sec/megaparsec, but are now more than twice as precise.The Hubble measurement, conducted by the SHOES (Supernova H0 for the Equation of State) Team and led by Adam Riess, of the Space Telescope Science Institute and the Johns Hopkins University, uses a number of refinements to streamline and strengthen the construction of a cosmic “distance ladder,” a billion light-years in length, that astronomers use to determine the universe’s expansion rate.Hubble observations of the pulsating Cepheid variables in a nearby cosmic mile marker, the galaxy NGC 4258, and in the host galaxies of recent supernovae, directly link these distance indicators. The use of Hubble to bridge these rungs in the ladder eliminated the systematic errors that are almost unavoidably introduced by comparing measurements from different telescopes. Steps to the Hubble Constant. Credit: NASA, ESA, and A. Feild (STScI)Riess explains the new technique: “It’s like measuring a building with a long tape measure instead of moving a yard stick end over end. You avoid compounding the little errors you make every time you move the yardstick. The higher the building, the greater the error.” Lucas Macri, professor of physics and astronomy at Texas A&M, and a significant contributor to the results, said, “Cepheids are the backbone of the distance ladder because their pulsation periods, which are easily observed, correlate directly with their luminosities. Another refinement of our ladder is the fact that we have observed the Cepheids in the near-infrared parts of the electromagnetic spectrum where these variable stars are better distance indicators than at optical wavelengths.”This new, more precise value of the Hubble constant was used to test and constrain the properties of dark energy, the form of energy that produces a repulsive force in space, which is causing the expansion rate of the universe to accelerate.By bracketing the expansion history of the universe between today and when the universe was only approximately 380,000 years old, the astronomers were able to place limits on the nature of the dark energy that is causing the expansion to speed up. (The measurement for the far, early universe is derived from fluctuations in the cosmic microwave background, as resolved by NASA’s Wilkinson Microwave Anisotropy Probe, WMAP, in 2003.)Their result is consistent with the simplest interpretation of dark energy: that it is mathematically equivalent to Albert Einstein’s hypothesized cosmological constant, introduced a century ago to push on the fabric of space and prevent the universe from collapsing under the pull of gravity. (Einstein, however, removed the constant once the expansion of the universe was discovered by Edwin Hubble.) Detail from NGC 3021. Credit: NASA, ESA, and A. Riess (STScI/JHU)“If you put in a box all the ways that dark energy might differ from the cosmological constant, that box would now be three times smaller,” says Riess. “That’s progress, but we still have a long way to go to pin down the nature of dark energy.” Though the cosmological constant was conceived of long ago, observational evidence for dark energy didn’t come along until 11 years ago, when two studies, one led by Riess and Brian Schmidt of Mount Stromlo Observatory, and the other by Saul Perlmutter of Lawrence Berkeley National Laboratory, discovered dark energy independently, in part with Hubble observations. Since then astronomers have been pursuing observations to better characterize dark energy.Riess’s approach to narrowing alternative explanations for dark energy—whether it is a static cosmological constant or a dynamical field (like the repulsive force that drove inflation after the big bang)—is to further refine measurements of the universe’s expansion history.Before Hubble was launched in 1990, the estimates of the Hubble constant varied by a factor of two. In the late 1990s the Hubble Space Telescope Key Project on the Extragalactic Distance Scale refined the value of the Hubble constant to an error of only about ten percent. This was accomplished by observing Cepheid variables at optical wavelengths out to greater distances than obtained previously and comparing those to similar measurements from ground-based telescopes.The SHOES team used Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) and the Advanced Camera for Surveys (ACS) to observe 240 Cepheid variable stars across seven galaxies. One of these galaxies was NGC 4258, whose distance was very accurately determined through observations with radio telescopes. The other six galaxies recently hosted Type Ia supernovae that are reliable distance indicators for even farther measurements in the universe. Type Ia supernovae all explode with nearly the same amount of energy and therefore have almost the same intrinsic brightness.By observing Cepheids with very similar properties at near-infrared wavelengths in all seven galaxies, and using the same telescope and instrument, the team was able to more precisely calibrate the luminosity of supernovae. With Hubble’s powerful capabilities, the team was able to sidestep some of the shakiest rungs along the previous distance ladder involving uncertainties in the behavior of Cepheids.Riess would eventually like to see the Hubble constant refined to a value with an error of no more than one percent, to put even tighter constraints on solutions to dark energy.Source: Space Telescope Science Institutecopyright http://www.universetoday.com/2009/05/07/astronomers-closing-in-on-dark-energy-with-refined-hubble-constant/hubble-constant/dark matter


Hubble Provides New Evidence For Dark Matter Around Small Galaxies.

ScienceDaily (Mar. 13, 2009) — NASA’s Hubble Space Telescope has uncovered a strong new line of evidence that galaxies are embedded in halos of dark matter.Peering into the tumultuous heart of the nearby Perseus galaxy cluster, Hubble discovered a large population of small galaxies that have remained intact while larger galaxies around them are being ripped apart by the gravitational pull of neighbouring galaxies. The results appear in the March 1st edition of the journal Monthly Notices of the Royal Astronomical Society.Dark matter is an invisible form of matter that accounts for most of the Universe’s mass. Astronomers have deduced the existence of dark matter by observing its gravitational influence on normal matter which consists of stars, gas, and dust.The Hubble images provide further evidence that the undisturbed galaxies are enshrouded by a “cushion” of dark matter, which protects them from their rough-and-tumble neighbourhood.“We were surprised to find so many dwarf galaxies in the core of this cluster that were so smooth and round and had no evidence at all of any kind of disturbance,” says astronomer Christopher Conselice of the University of Nottingham, and leader of the Hubble observations. “These dwarfs are very old galaxies that have been in the cluster a long time. So if something was going to disrupt them, it would have happened by now. They must be very, very dark matter dominated galaxies.”The dwarf galaxies may have even a higher amount of dark matter than spiral galaxies. “With these results, we cannot say whether the dark-matter content of the dwarfs is higher than in the Milky Way Galaxy,” Conselice says. “Although, the fact that spiral galaxies are destroyed in clusters, while the dwarfs are not, suggests that is indeed the case.”First proposed about 80 years ago, dark matter is thought to be the “glue” that holds galaxies together. Astronomers suggest that dark matter provides vital “scaffolding” for the Universe, forming a framework for the formation of galaxies through gravitational attraction. Previous studies with Hubble and NASA’s Chandra X-ray Observatory found evidence of dark matter in entire clusters of galaxies such as the Bullet Cluster. The new Hubble observations continue the search for dark matter in individual galaxies.Observations by Hubble’s Advanced Camera for Surveys spotted 29 dwarf elliptical galaxies in the Perseus Cluster located 250 million light-years away and one of the closest galaxy clusters to Earth. Of those galaxies 17 are new discoveries.Because dark matter cannot be seen astronomers detected its presence through indirect evidence. The most common method is by measuring the velocities of individual stars or groups of stars as they move randomly in the galaxy or as they rotate around the galaxy. The Perseus Cluster is too far away for telescopes to resolve individual stars and measure their motions. So Conselice and his team derived a new technique for uncovering dark matter in these dwarf galaxies by determining the minimum mass the dwarfs must have to protect them from being disrupted by the strong tidal pull of gravity from larger galaxies.Studying these small galaxies in detail was possible only because of the sharpness of Hubble’s Advanced Camera for Surveys. Conselice and his team first spied the galaxies with the WIYN Telescope at Kitt Peak National Observatory outside Tucson, Arizona. Those observations, Conselice says, only hinted that many of the galaxies were smooth and therefore dark-matter dominated. “Those ground-based observations could not resolve the galaxies, so we needed Hubble imaging to nail it,” he says.Other team members are Samantha J. Penny of the University of Nottingham; Sven De Rijcke of the University of Ghent in Belgium; and Enrico Held of the University of Padua in Italy.COPYRIGHT http://www.sciencedaily.com/releases/2009/03/090312093947.htmDARK MATTER


Dark matter filaments stoked star birth in early galaxies

18:58 21 January 2009 by Rachel Courtland Tendrils of dark matter channelled gas deep into the hearts of some of the universe's earliest galaxies, a new computer simulation suggests. The result could explain how some massive galaxies created vast numbers of stars without gobbling up their neighbours.Dramatic bursts of star formation are thought to occur when galaxies merge and their gas collides and heats up. Evidence of these smash-ups is fairly easy to spot, since they leave behind mangled pairs of galaxies that eventually merge, their gas settling into a bright, compact centre.But several years ago, astronomers began finding disc-like galaxies with crowded stellar nurseries that seemed to bear no hallmarks of a past collision. These galaxies, which thrived when the universe was just 3 billion years old, were at least as massive as the Milky Way, but created stars at some 50 times our galaxy's rate.Blow awayIt was not clear how these galaxies could harbour such intense bursts of star formation without collisions. Smaller galaxies are thought to form when gas falls in from all directions. But this process would not work with larger galaxies - those about the Milky Way's size or heavier. These galaxies grow so hot and dense they create a shock-wave-like barrier that heats incoming gas and prevents it from falling in.But Avishai Dekel of Hebrew University in Jerusalem thinks an influx of gas could be responsible for the star formation after all. This gas could flow along filaments of dark matter that make up a cosmic web still seen today in the distribution of galaxies across the sky.Dekel and colleagues used fluid dynamics simulations to model the cosmic web of gas and dark matter at a time when the universe was some 3 billion years old. They tracked how gas accumulated in galaxies lying at the nodes of the web, where dark matter filaments intersect.Shock resistantThe team found that gas in the tendrils was so dense that collisions between particles would dissipate energy quickly, making it less susceptible to shocks in the surrounding, hotter gas. The cool gas could then fall into the galaxy's disc fast enough to fuel dramatic starbursts."We found the gas can penetrate all the way through the hot material," Dekel told New Scientist. "This is solving the riddle of where this star formation is coming from."Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, says the explanation could work, but adds that the simulation cannot estimate how rapidly the gas can be converted to stars, which would be a crucial test.More detailed simulations and studies of the galaxies themselves could confirm the model. "We need more time to test it out, but it smells like the right answer," Genzel told New Scientist.copyright URL http://www.newscientist.com/article/dn16462-dark-matter-filaments-stoked-star-birth-in-early-galaxies.htmlDARK MATTER


Astronomers Aim to Grasp Mysterious Dark Matter

By Clara MoskowitzSpecial to SPACE.composted: 29 December 20089:02 am ET For the past quarter century, dark matter has been a mystery we've just had to live with. But the time may be getting close when science can finally unveil what this befuddling stuff is that makes up most of the matter in the universe.Dark matter can't be seen. Nobody even knows what it is. But it must be there, because without it galaxies would fly apart.Upcoming experiments on Earth such as the Large Hadron Collider (LHC) particle accelerator in Switzerland, and a new spacecraft called Gaia set to launch in 2011, could be the key to closing the case on one of the biggest unsolved mysteries in science.A disturbing truth is accepted by most astronomers: There is a lot more stuff in the universe than what we can see. Scientists now think visible matter — all the planets, stars, and galaxies that shine down on us — represents only about 4 percent of the mass-energy budget of the universe, while dark matter and its even more esoteric cousin, dark energy, make up the rest."There is no consensus actually at all as to what dark matter is," said Gerard Gilmore, an astronomer at the University of Cambridge who wrote a recent essay for the Dec. 5 issue of the journal Science about the search for dark matter.A leading hypothesis posits that dark matter is composed of some kind of exotic particle, yet to be detected, that doesn't interact with light, so we can't see it. One such theorized class of particles is called WIMPs (Weakly interacting massive particles), which are thought to be neutral in charge and weigh more than 100 times the mass of a proton.Atom smasherThe newly-opened LHC, a 17-mile-long (27 kilometer-long) underground ring in which sprays of protons speed around and crash into each other, could be the first experiment to detect WIMPS. The particle accelerator officially went online in September 2008, but was halted shortly after due to a fault with its construction — it's due to go back online in the summer of 2009. Since the LHC is the largest and most powerful atom smasher ever built, its collisions could produce the extremely high energies needed to create the elusive particles.In fact, the LHC will likely create a host of never-before-seen particles, opening up a realm of the universe that physicists have been eager to explore. "The assumption is, there will be whole families of new types of particles," Gilmore said in a podcast interview with a reporter from Science. "The challenge then is to say, well OK, we now then have a new set of ingredients in our recipe for how nature is put together, but what is the recipe that uses this set of ingredients? I.e., what mix of these particles does nature actually use to create the universe, and how?"Weighing the universeThat's where Gaia comes in. The European Space Agency satellite is designed to measure positions and speeds of about 1 billion nearby stars with unprecedented precision. Its vision is so sharp it should be able to discern the equivalent of a shirt button on the surface of the moon as seen from Earth, Gilmore said.By establishing where things are in our galaxy, the spacecraft will help scientists measure the weight and distribution of mass in the Milky Way in much greater detail than ever before. These measurements are vital for models that attempt to describe how the pull of dark matter has shaped our galaxy."What Gaia will do is measure the distances of stuff and measure how they're moving in three dimensions around space to much better precision than we've had before, which will allow us to weigh things on all sorts of scales down to the smallest scales we can find," Gilmore said. "They will tell us to exquisite precision how the dark matter is distributed in space, which is the recipe we need to determine its properties."COPYRIGHT www.space.com URL http://www.space.com/scienceastronomy/081229-mm-dark-matter.htmlig263_hubble_04_02


What came before the Big Bang ?

A question that has been pondered by scientists and philosophers alike could soon be answered, thanks to a mathematical model that explains an anomaly in the early Universe."It's no longer completely crazy to ask what happened before the Big Bang," says Marc Kamionkowski, Caltech's Robinson Professor of Theoretical Physics and Astrophysics. Kamionkowski and colleagues propose a mathematical model to explain an anomaly in what is widely believed to be a Universe of uniformly distributed radiation and matter. WMAP’s all-sky picture of the infant Universe reveals 13.7 billion year old temperature fluctuations (shown as colour differences) that correspond to the seeds that grew to become the galaxies. These variations are 'lop-sided' suggesting asymmetric density variations. Image: NASA / WMAP Science Team.The notion of space expanding exponentially from a blank canvas in the instant following the so-called Big Bang is known as inflation, and the simplest interpretation of the theory requires the Universe to be uniform in all directions. The energy that permeated the Universe 400,000 years after the Big Bang – essentially an ‘echo’ from the Big Bang – is known as the Cosmic Microwave Background, or CMB, and was mapped in detail by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP), revealing that tiny fluctuations in the CMB seemed to be the same everywhere, fitting with the theory of inflation. "If your eyes measured radio frequency, you'd see the entire sky glowing. This is what WMAP sees," describes Kamionkowksi. WMAP depicts the CMB as an afterglow of light that has decayed to microwave radiation as the Universe expanded over the past 13.7 billion years.The problem with inflation, however, is that it predicts the Universe began uniformly, and earlier this year a detailed study suggested that there is in fact a pronounced asymmetry in the CMB, with intensely varied deviations from the average value in one half of the sky than the other. "It's a certified anomaly," remarks Kamionkowski. "But since inflation seems to do so well with everything else, it seems premature to discard the theory." A representation of the evolution of the Universe over 13.7 billion years. The far left depicts the earliest moment we can now probe, when a period of inflation produced a burst of exponential growth in the Universe. Image: NASA/WMAP Science Team.The team are now trying to address the remarkable asymmetry within the bounds of inflation. They began by testing whether the value of a single energy field thought to have driven inflation, called the inflaton, was different on one side of the Universe than the other. But by changing the mean value of the inflation, the mean temperature and amplitude of energy variations in space also changed, violating constraints to the homogeneity of the Universe. So they explored a second energy field, called the curvaton, which has already been proposed to give rise to the density fluctuations observed in the CMB. The team introduced a perturbation to the curvaton field that turns out to affect only how temperature varies from point to point through space, while preserving its average value. This new model suggests more cold than hot spots in the CMB, a predication that will be tested by ESA’s Planck satellite that is scheduled to launch in April 2009."Inflation is a description of how the Universe expanded," says Adrienne Erickcek, a graduate student working on the project. "Its predictions have been verified, but what drove it and how long did it last? This is a way to look at what happened during inflation, which has a lot of blanks waiting to be filled in."Furthermore, the theoretical perturbation that the researchers introduced to the model may also offer the first glimpse at what came before the Big Bang, because it could represent an imprint inherited from the time before inflation. That is, it could be a signature of a structure left over from something that produced our Universe. Perhaps an older universe from which our own Universe was born could explain this anomaly, or could it be due to concurrently existing universes – a Multiverse – in which there are big bangs occurring at different points in the Universe at different times, generating a number of separate universes within our Multiverse?"All of that stuff is hidden by a veil, observationally," says Kamionkowski. "If our model holds up, we may have a chance to see beyond this veil."With the launch of Planck not far off we may not have too long to wait for the answers to the questions posed by Kamionkowski and others, and of the nature of how our Universe came to be. The study appears in the 16 December edition of the journal Physical Review D.COPYRIGHT URL http://astronomynow.com/081208WhatcamebeforetheBigBang.htmlbigbang2


Caltech Researchers Interpret Asymmetry in Early Universe

PASADENA, Calif.--The Big Bang is widely considered to have obliterated any trace of what came before. Now, astrophysicists at the California Institute of Technology (Caltech) think that their new theoretical interpretation of an imprint from the earliest stages of the universe may also shed light on what came before. "It's no longer completely crazy to ask what happened before the Big Bang," comments Marc Kamionkowski, Caltech's Robinson Professor of Theoretical Physics and Astrophysics. Kamionkowski joined graduate student Adrienne Erickcek and senior research associate in physics Sean Carroll to propose a mathematical model explaining an anomaly in what is supposed to be a universe of uniformly distributed radiation and matter. Their investigations turn on a phenomenon called inflation, first proposed in 1980, which posits that space expanded exponentially in the instant following the Big Bang. "Inflation starts the universe with a blank slate," Erickcek describes. The hiccup in inflation, however, is that the universe is not as uniform as the simplest form of the theory predicts it to be. Some parts of it are more intensely varied than others. Until recently, measurements of the Cosmic Microwave Background (CMB) radiation, a form of electromagnetic radiation that permeated the universe 400,000 years after the Big Bang, were consistent with inflation--miniscule fluctuations in the CMB seemed to be the same everywhere. But a few years ago, some researchers, including a group led by Krzysztof Gorski of NASA's Jet Propulsion Laboratory, which is managed by Caltech, scrutinized data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP). They discovered that the amplitude of fluctuations in the CMB is not the same in all directions. "If your eyes measured radio frequency, you'd see the entire sky glowing. This is what WMAP sees," Kamionkowksi describes. WMAP depicts the CMB as an afterglow of light from shortly after the Big Bang that has decayed to microwave radiation as the universe expanded over the past 13.7 billion years. The probe also reveals more pronounced mottling--deviations from the average value--in the CMB in one half of the sky than the other. "It's a certified anomaly," Kamionkowski remarks. "But since inflation seems to do so well with everything else, it seems premature to discard the theory." Instead, the team worked with the theory in their math addressing the asymmetry. They started by testing whether the value of a single energy field thought to have driven inflation, called the inflaton, was different on one side of the universe than the other. It didn't work--they found that if they changed the mean value of the inflaton, then the mean temperature and amplitude of energy variations in space also changed. So they explored a second energy field, called the curvaton, which had been previously proposed to give rise to the fluctuations observed in the CMB. They introduced a perturbation to the curvaton field that turns out to affect only how temperature varies from point to point through space, while preserving its average value. The new model predicts more cold than hot spots in the CMB, Kamionkowski says. Erickcek adds that this prediction will be tested by the Planck satellite, an international mission led by the European Space Agency with significant contributions from NASA, scheduled to launch in April 2009. For Erickcek, the team's findings hold the key to understanding more about inflation. "Inflation is a description of how the universe expanded," she adds. "Its predictions have been verified, but what drove it and how long did it last? This is a way to look at what happened during inflation, which has a lot of blanks waiting to be filled in." But the perturbation that the researchers introduced may also offer the first glimpse at what came before the Big Bang, because it could be an imprint inherited from the time before inflation. "All of that stuff is hidden by a veil, observationally," Kamionkowski says. "If our model holds up, we may have a chance to see beyond this veil." The study appears December 16 in the journal Physical Review D. It was supported by the Department of Energy and by Caltech's Moore Center for Theoretical Cosmology and Physics. ### Contact: Martin Voss (626) 395-8733 mvoss@caltech.edu Visit the Caltech Media Relations website at http://pr.caltech.edu/media.WMAP Copyright Caltech Press Releases URL http://mr.caltech.edu/media/Press_Releases/PR13218.html


Dark Energy Found Stifling Growth in the Universe

WASHINGTON -- For the first time, astronomers have clearly seen the effects of "dark energy" on the most massive collapsed objects in the universe using NASA's Chandra X-ray Observatory. By tracking how dark energy has stifled the growth of galaxy clusters and combining this with previous studies, scientists have obtained the best clues yet about what dark energy is and what the destiny of the universe could be. This work, which took years to complete, is separate from other methods of dark energy research such as supernovas. These new X-ray results provide a crucial independent test of dark energy, long sought by scientists, which depends on how gravity competes with accelerated expansion in the growth of cosmic structures. Techniques based on distance measurements, such as supernova work, do not have this special sensitivity. Scientists think dark energy is a form of repulsive gravity that now dominates the universe, although they have no clear picture of what it actually is. Understanding the nature of dark energy is one of the biggest problems in science. Possibilities include the cosmological constant, which is equivalent to the energy of empty space. Other possibilities include a modification in general relativity on the largest scales, or a more general physical field. To help decide between these options, a new way of looking at dark energy is required. It is accomplished by observing how cosmic acceleration affects the growth of galaxy clusters over time. "This result could be described as 'arrested development of the universe'," said Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass., who led the research. "Whatever is forcing the expansion of the universe to speed up is also forcing its development to slow down." Vikhlinin and his colleagues used Chandra to observe the hot gas in dozens of galaxy clusters, which are the largest collapsed objects in the universe. Some of these clusters are relatively close and others are more than halfway across the universe. The results show the increase in mass of the galaxy clusters over time aligns with a universe dominated by dark energy. It is more difficult for objects like galaxy clusters to grow when space is stretched, as caused by dark energy. Vikhlinin and his team see this effect clearly in their data. The results are remarkably consistent with those from the distance measurements, revealing general relativity applies, as expected, on large scales. "For years, scientists have wanted to start testing how gravity works on large scales and now, we finally have," said William Forman, a co-author of the study from the Smithsonian Astrophysical Observatory. "This is a test that general relativity could have failed." When combined with other clues -- supernovas, the study of the cosmic microwave background, and the distribution of galaxies -- this new X-ray result gives scientists the best insight to date on the properties of dark energy. The study strengthens the evidence that dark energy is the cosmological constant. Although it is the leading candidate to explain dark energy, theoretical work suggests it should be about 10 raised to the power of 120 times larger than observed. Therefore, alternatives to general relativity, such as theories involving hidden dimensions, are being explored. "Putting all of this data together gives us the strongest evidence yet that dark energy is the cosmological constant, or in other words, that 'nothing weighs something'," said Vikhlinin. "A lot more testing is needed, but so far Einstein's theory is looking as good as ever." These results have consequences for predicting the ultimate fate of the universe. If dark energy is explained by the cosmological constant, the expansion of the universe will continue to accelerate, and the Milky Way and its neighbor galaxy, Andromeda, never will merge with the Virgo cluster. In that case, about a hundred billion years from now, all other galaxies ultimately would disappear from the Milky Way's view and, eventually, the local superclusters of galaxies also would disintegrate. The work by Vikhlinin and his colleagues will be published in two separate papers in the Feb. 10 issue of The Astrophysical Journal. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass. Additional information and images are available at: http://chandra.nasa.gov http://chandra.harvard.edu Copyright : nasa : url : http://www.nasa.gov/home/hqnews/2008/dec/HQ_08329_DARK_ENERGY.html0_61_050322_dark_energy