08-10-11

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.

 

copyright :

 

http://upload.wikimedia.org/wikipedia/commons/thumb/7/7d/...

 

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.

 

copyright :

 

http://blogs.nature.com/news/2011/10/post_85.htm

l

 

26-06-11

Multiverse From Wikipedia, the free encyclopedia

cosmology,multiverse,

copyright :

http://commons.wikimedia.org/wiki/File:Multiverse.jpg

 

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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http://en.wikipedia.org/wiki/Multiverse

 

20-06-11

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

 

cosmology, antimatter,cern

copyright :


http://commons.wikimedia.org/wiki/File:3D_image_of_Antihy...


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.


copyright :

 

http://www.sciencedaily.com/releases/2011/03/110328101306...

 

20-04-11

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

 

 

anti-gravity,dark energy,cosmology

copyright :


http://commons.wikimedia.org/wiki/File:NGC_3021_Hubble.jp...

 

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.

 

copyright :


http://www.universetoday.com/84934/antigravity-could-repl...

 

17-03-11

NASA Prepares Antimatter-Hunting Detector for Space Shuttle Launch

 

16 March 2011

 

 

cosmologyn,dark matter,AMS,Space Shuttle,ISS

copyright image :

http://commons.wikimedia.org/wiki/File:AMS-01.jpg?uselang...

 

 

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.

 

copyright :


http://www.space.com/11149-nasa-antimatter-detector-shutt...

26-02-11

Dark Matter: New Evidence on How Galaxies Are Born

 

By Michael D. Lemonick Wednesday, Feb. 23, 2011

 

dark matter,halo,cosmology

Copyright : http://commons.wikimedia.org/wiki/File:Hs-2007-17-a-full_...

 

If you think it's hard to swallow the concept of dark matter, you're not alone.

 

Decades ago, a few astronomers began to suspect that the universe was swarming with some mysterious, invisible substance that was yanking galaxies around with its own powerful gravity.

 

And for those same decades, most of those astronomers' colleagues dismissed the notion as pretty much nuts.

 

But the evidence kept mounting, and nowadays dark matter is a firmly established concept in modern astrophysics.

 

It pretty much has to exist, in fact, to explain why individual galaxies spin as fast as they do without flying apart, and why groups of galaxies move the way they do in relation to one another.

 

If there weren't 10 times as much dark matter as there are stars and gas clouds and other visible matter, the universe would make no sense.

 

Nature abhors irrationality, and so we live in a universe in which just about every galaxy, including the Milky Way, is held safely inside a huge blob of dark matter like a butterfly floating inside a glass paperweight.

 


Copyright and Read more

 

http://www.time.com/time/health/article/0,8599,2052614,00...

 

 

 

18-02-11

Dark energy is not directly detectable, but scientists can track its footsteps through history.

 

dark matter,the hunt,cosmology

 

copyright

http://upload.wikimedia.org/wikipedia/commons/c/c9/Dark_m...

 

A massive survey of distant galaxies should help unravel a mind-bending cosmic mystery: Why has the expansion of the universe sped up ?


copyright

http://news.discovery.com/space/dark-energy-galaxies-univ...

 

 

17-02-11

Herschel finds less dark matter but more stars

 

dark matter,Herschel

copyright

http://upload.wikimedia.org/wikipedia/commons/9/9d/Struct...


16 February 2011

 

ESA’s Herschel space observatory has discovered a population of dust-enshrouded galaxies that do not need as much dark matter as previously thought to collect gas and burst into star formation.

 

copyright

http://www.esa.int/esaCP/SEMRQ3PT1KG_index_0.html

 

 

28-01-11

Hunt for dark matter closes in at Large Hadron Collider

 

Wednesday 26 January 2011


Physicists are closer than ever to finding the source of the Universe's mysterious dark matter, following a better than expected year of research at the Compact Muon Solenoid (CMS) particle detector, part of the Large Hadron Collider (LHC) at CERN in Geneva.

 

cern,lhc,cms,dark matter

 


copyright

http://commons.wikimedia.org/wiki/File:LHC,_CERN.jpg?usel...

Max Braun on Flickr

 

 

The scientists have now carried out the first full run of experiments that smash protons together at almost the speed of light.

 

When these sub-atomic particles collide at the heart of the CMS detector, the resultant energies and densities are similar to those that were present in the first instants of the Universe, immediately after the Big Bang some 13.7 billion years ago.

 

The unique conditions created by these collisions can lead to the production of new particles that would have existed in those early instants and have since disappeared.

 

The researchers say they are well on their way to being able to either confirm or rule out one of the primary theories that could solve many of the outstanding questions of particle physics, known as Supersymmetry (SUSY).

 

Many hope it could be a valid extension for the Standard Model of particle physics, which describes the interactions of known subatomic particles with astonishing precision but fails to incorporate general relativity, dark matter and dark energy.

 

Dark matter is an invisible substance that we cannot detect directly but whose presence is inferred from the rotation of galaxies.

 

Physicists believe that it makes up about a quarter of the mass of the Universe whilst the ordinary and visible matter only makes up about 5% of the mass of the Universe.

 

Its composition is a mystery, leading to intriguing possibilities of hitherto undiscovered physics.

 

Professor Geoff Hall from the Department of Physics at Imperial College London, who works on the CMS experiment, said:

"We have made an important step forward in the hunt for dark matter, although no discovery has yet been made.

 

These results have come faster than we expected because the LHC and CMS ran better last year than we dared hope and we are now very optimistic about the prospects of pinning down Supersymmetry in the next few years."

 


copyright :

 

http://www3.imperial.ac.uk/newsandeventspggrp/imperialcol...

 

 

 

16-01-11

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

 

Copyright :

http://upload.wikimedia.org/wikipedia/commons/f/fd/Our_Mi...

 

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...

 

14-01-11

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

 

17-12-10

Physicists propose mechanism that explains the origins of both dark matter and 'normal' matter

 

December 10, 2010 by Lisa Zyga Enlarge

 

Defining_Dark_Matter_and_Energy_in_a_4th_Etheric_System.png

 

WIKIMEDIA COMMONS IMAGE

 

(PhysOrg.com) -- Through precise cosmological measurements, scientists know that about 4.6% of the energy of the Universe is made of baryonic matter (normal atoms), about 23% is made of dark matter, and the remaining 72% or so is dark energy.

 

Scientists also know that almost all the baryonic matter in the observable Universe is matter (with a positive baryon charge) rather than antimatter (with a negative baryon charge).

 

But exactly why this matter and energy came to be this way is still an open question.

 

In a recent study, physicists have proposed a new mechanism that can generate both the baryon asymmetry and the dark matter density of the Universe simultaneously.

 

 


copyright - credits :


http://www.physorg.com/news/2010-12-physicists-mechanism-...

 

14-12-10

No evidence of time before Big Bang.

Published online 10 December 2010 | Nature | doi:10.1038/news.2010.665

 

Latest research deflates the idea that the Universe cycles for eternity.

 

Edwin Cartlidge


Circular ripples in the cosmic microwave background have been making waves with theoreticians.

 

NASA

Our view of the early Universe may be full of mysterious circles — and even triangles — but that doesn't mean we're seeing evidence of events that took place before the Big Bang.

 

So says a trio of papers taking aim at a recent claim that concentric rings of uniform temperature within the cosmic microwave background — the radiation left over from the Big Bang — might, in fact, be the signatures of black holes colliding in a previous cosmic 'aeon' that existed before our Universe.

 

Dark_matter_halo.png

Dark Matter Halo

WIKIMEDIA COMMONS

 


copyright - credits : http://www.nature.com/news/2010/101210/full/news.2010.665...

26-11-10

Mini-oerknak resulteert in superhete vloeistof (LHC - CERN)

25 november 2010


allesoversterrenkunde.nl
 

 

IMAGE.jpg

 

copyright - credits


http://www.scienceparkamsterdam.nl/onderzoek/nieuwsberich...

 

Kort na de oerknal was het heelal een extreem dikke, superhete vloeistof.

 

Dat is de verrassende ontdekking die onderzoekers hebben gedaan met de Large Hadron Collider (LHC), de grote deeltjesversneller in Zwitserland.


Op 7 november begonnen wetenschappers een nieuw experiment met de LHC, waarbij zij de kernen van loodatomen met enorme snelheden tegen elkaar lieten botsen.


Bij die botsingen ontstonden kleine vuurballen van subatomaire deeltjes met een temperatuur van meer dan 10 biljoen graden.
 

Het idee achter dit experiment was om de 'oersoep' van deeltjes te reproduceren, het zogeheten quark-gluonenplasma, zoals die een miljoenste seconde na het
ontstaan van het heelal moet hebben bestaan.


Quarks en gluonen zijn de bouwstenen van de neutronen en protonen die de atomen vormen.


Volgens veel modellen die de deeltjesstroom van dit subatomaire vuurwerk beschrijven, zou deze oersoep zich als een gas moeten gedragen.


Maar uit de waarnemingen blijkt nu dat de oersoep, precies zoals de naam al aangeeft, meer weg had van een vloeistof.


Ook de dichtheid van de subatomaire deeltjes die bij de botsingen vrijkwamen, verrast de onderzoekers: bij de 'mini-oerknallen' werden veel meer van die
deeltjes gevormd dan verwacht.


Het is volgende wetenschappers overigens nog te vroeg om uit deze eerste resultaten verregaande conclusies te trekken over de structuur van het jonge heelal.

 

© Eddy Echternach

www.astronieuws.nl

 

copyright-credits

http://allesoversterrenkunde.nl/nieuws/4274-Mini-oerknak-...

 

 

25-11-10

What is Dark Energy ?

by Clara Moskowitz


27th april 2010


Dark energy is the name given to an unexplained force that is drawing galaxies away from each other, against the pull of gravity, at an accelerated pace.

 

Dark energy is a bit like anti-gravity. Where gravity pulls things together at the more local level, dark energy tugs them apart on the grander scale.

 

Dark Matter and Dark Energy.png


Dark Matter and Dark Energy Simplified Structure

 

Its existence isn't proven, but dark energy is many scientists' best guess to explain the confusing observation that the universe's expansion is speeding up.

 

Experts still don't know what's driving this force, but the quest to learn more about dark energy is one of cosmologists' top priorities.


Copyright - credits for article : http://www.space.com/scienceastronomy/090427-mm-dark-ener...


Copyright - credits photo : commons.wikimedia.org

 

URL Photo :

 

http://commons.wikimedia.org/wiki/File:Defining_Darkc_Mat...

22-11-10

Penrose: WMAP Shows Evidence of ‘Activity’ Before Big Bang

22nd November 2010


Have scientists seen evidence of time before the Big Bang, and perhaps a verification of the idea of the cyclical universe?


One of the great physicists of our time, Roger Penrose from the University of Oxford, has published a new paper saying that the circular patterns seen in the WMAP mission data on the Cosmic Microwave Background suggest that space and time perhaps did not originate at the Big Bang but that our universe continually cycles through a series of “aeons,” and we have an eternal, cyclical cosmos.


His paper also refutes the idea of inflation, a widely accepted theory of a period of very rapid expansion immediately following the Big Bang.

 

Sir Roger Penrose.jpg

 

Copyright - Credits : Universe Today

 

http://www.universetoday.com/79750/penrose-wmap-shows-evi... 

 

12-11-10

Hubble Provides Most Detailed Dark Matter Map Yet

 

11th November 2010

 

DarkMatterAbell.jpg

 

Nasa Hubble Space Telescope shows the distribution of dark matter in the center of the giant galaxy cluster Abell 1689. (more than 1000 galaxies with trillions of stars).

 

Credit: NASA, ESA, D. Coe (NASA Jet Propulsion Laboratory/California Institute of Technology,
and Space Telescope Science Institute), N. Benitez (Institute of Astrophysics of Andalusia, Spain), T. Broadhurst (University of the Basque Country, Spain), and H. Ford (Johns Hopkins University).

 

Credits :

 

http://www.universetoday.com/78309/hubble-provides-most-d...

 

11-11-10

Cosmology - animation photo from Big Bang To Present Time

FromBigBangtopresenttime.jpg

25-09-10

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.

Dimensies.jpg

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.’

9_Dimensions.jpg

 

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.

 

Botsingsexperimenten

 

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

 

Copyright

 

http://allesoversterrenkunde.nl/artikelen/1004-Doorbraak-...

 

 

18-09-10

Astronomen nemen afscheid van oerknalsatelliet WMAP !

 

13 september 2010

 

copyright

 

allesoversterrenkunde.nl

 

http://allesoversterrenkunde.nl/nieuws/4117-Astronomen-ne...

 

WMAP.jpg

 

Zonder veel ophef hebben astronomen op 8 september afscheid genomen van de Wilkinson Microwave Anisotropy Probe, beter bekend als WMAP.

 

De satelliet, die negen jaar lang de zogeheten kosmische achtergrondstraling heeft onderzocht, is met zijn eigen raketmotor in een veilige baan om de zon gemanoeuvreerd.

 

De WMAP-satelliet werd op 30 juni 2001 gelanceerd naar 'vaste' locatie die vanaf de zon gezien anderhalf miljoen kilometer achter de aarde ligt.

 

Enkele maanden later begon hij met het in kaart brengen van de kosmische achtergrondstraling - de straling die een overblijfsel is van de oerknal, die bijna veertien miljard jaar geleden het ontstaan van het heelal inluidde.

 

Al in 2003 werd WMAP door het wetenschappelijke tijdschrift Science uitgeroepen tot 'doorbraak van het jaar'.

 

De resultaten van de WMAP-metingen zijn in overeenstemming met het standaardmodel dat vrijwel alle astronomen voor het ontstaan van het heelal hanteren.

 

Vastgesteld is dat de oerknal waaruit ons heelal is voortgekomen 13,73 miljard jaar geleden moet hebben plaatsgevonden.

 

Ook is uit het onderzoek gebleken dat het heelal voor slechts 4,6 procent uit normale materie bestaat.

 

 

 

UniversePie.jpg

De overige 95,4 procent wordt gevormd door donkere materie, die geen enkele vorm van waarneembare straling uitzendt maar wel zwaartekracht uitoefent, en een mysterieuze donkere energie, die het heelal versneld laat uitdijen.

 

Toegevoegd door Eddy Echternach

 

www.astronieuws.nl

 

Links

 

http://nl.wikipedia.org/wiki/Wilkinson_Microwave_Anisotro...

 

http://map.gsfc.nasa.gov/

12-09-10

Laws of physics may change across the universe

 

18:29 08 September 2010 by Michael Brooks

 

New evidence supports the idea that we live in an area of the universe that is "just right" for our existence.

 

The controversial finding comes from an observation that one of the constants of nature appears to be different in different parts of the cosmos.

 

If correct, this result stands against Einstein's equivalence principle, which states that the laws of physics are the same everywhere.

 

"This finding was a real surprise to everyone," says John Webb of the University of New South Wales in Sydney, Australia.

 

Webb is lead author on the new paper, which has been submitted to Physical Review Letters.

 

Even more surprising is the fact that the change in the constant appears to have an orientation, creating a "preferred direction", or axis, across the cosmos.

 

That idea was dismissed more than 100 years ago with the creation of Einstein's special theory of relativity.

 

Sections of sky

 

At the centre of the new study is the fine structure constant, also known as alpha.

 

This number determines the strength of interactions between light and matter.

 

A decade ago, Webb used observations from the Keck telescope in Hawaii to analyse the light from distant galaxies called quasars.

 

The data suggested that the value of alpha was very slightly smaller when the quasar light was emitted 12 billion years ago than it appears in laboratories on Earth today.

 

Now Webb's colleague Julian King, also of the University of New South Wales, has analysed data from the Very Large Telescope (VLT) in Chile, which looks at a different region of the sky.

 

The VLT data suggests that the value of alpha elsewhere in the universe is very slightly bigger than on Earth.

 

The difference in both cases is around a millionth of the value alpha has in our region of space, and suggests that alpha varies in space rather than time. "

 

I'd quietly hoped we'd simply find the same thing that Keck found," King says. "This was a real shock."

 

 

Galaxies merging.jpg

 

 

 

 

 

 

 

 

 

 

 

Bar magnet

 

Moreover, the team's analysis of around 300 measurements of alpha in light coming from various points in the sky suggests the variation is not random but structured, like a bar magnet. The universe seems to have a large alpha on one side and a smaller alpha on the other.

 

This "dipole" alignment nearly matches that of a stream of galaxies mysteriously moving towards the edge of the universe.

 

It does not, however, line up with another unexplained dipole, dubbed the axis of evil, in the afterglow of the big bang.

Earth sits somewhere in the middle of the extremes for alpha. If correct, the result would explain why alpha seems to have the finely tuned value that allows chemistry – and thus life – to occur. Grow alpha by 4 per cent, for instance, and the stars would be unable to produce carbon, making our biochemistry impossible.

 

Extraordinary claim

 

Even if the result is accepted for publication, it is going to be hard to convince other scientists that the laws of physics might need a rewrite.

 

A spatial variation in the fine-structure constant would be "truly transformative", according to Lennox Cowie,

who works at the Institute for Astronomy in Hawaii.

 

But, he adds, extraordinary claims require extraordinary evidence: "That's way beyond what we have here."

 

He says the statistical significance of the new observations is too small to prove that alpha is changing.

 

If the interpretation of the light is correct, it is "a huge deal", agrees Craig Hogan, head of the Fermilab Center for Particle Astrophysics in Batavia, Illinois.

 

But like Cowie, he suspects there is a flaw somewhere in the analysis. "I think the result is not real," he says.

 

Another author on the paper, Michael Murphy of Swinburne University in Australia, understands the caution.

 

But he says the evidence for changing constants is piling up. "We just report what we find, and no one has been able to explain away these results in a decade of trying," Murphy told New Scientist.

 

"The fundamental constants being constant is an assumption. We're here to test physics, not to assume it."

 

Updated on 9 September: The analysis of VLT data was amended to credit Julian King

 


COPYRIGHT :


http://www.newscientist.com/article/dn19429-laws-of-physi...

25-04-10

OUR UNIVERSE AT HOME WITHIN A LARGER UNIVERSE

BY STAFF WRITERSBLOOMINGTON IN (SPX) APR 07, 2010300px-Worm3COULD OUR UNIVERSE BE LOCATED WITHIN THE INTERIOR OF A WORMHOLE WHICH ITSELF IS PART OF A BLACK HOLE THAT LIES WITHIN A MUCH LARGER UNIVERSE? SUCH A SCENARIO IN WHICH THE UNIVERSE IS BORN FROM INSIDE A WORMHOLE (ALSO CALLED AN EINSTEIN-ROSEN BRIDGE) IS SUGGESTED IN A PAPER FROM INDIANA UNIVERSITY THEORETICAL PHYSICIST NIKODEM POPLAWSKI IN PHYSICS LETTERS B. THE FINAL VERSION OF THE PAPER WAS AVAILABLE ONLINE MARCH 29 AND WILL BE PUBLISHED IN THE JOURNAL EDITION APRIL 12. POPLAWSKI TAKES ADVANTAGE OF THE EUCLIDEAN-BASED COORDINATE SYSTEM CALLED ISOTROPIC COORDINATES TO DESCRIBE THE GRAVITATIONAL FIELD OF A BLACK HOLE AND TO MODEL THE RADIAL GEODESIC MOTION OF A MASSIVE PARTICLE INTO A BLACK HOLE. IN STUDYING THE RADIAL MOTION THROUGH THE EVENT HORIZON (A BLACK HOLE'S BOUNDARY) OF TWO DIFFERENT TYPES OF BLACK HOLES - SCHWARZSCHILD AND EINSTEIN-ROSEN, BOTH OF WHICH ARE MATHEMATICALLY LEGITIMATE SOLUTIONS OF GENERAL RELATIVITY - POPLAWSKI ADMITS THAT ONLY EXPERIMENT OR OBSERVATION CAN REVEAL THE MOTION OF A PARTICLE FALLING INTO AN ACTUAL BLACK HOLE. BUT HE ALSO NOTES THAT SINCE OBSERVERS CAN ONLY SEE THE OUTSIDE OF THE BLACK HOLE, THE INTERIOR CANNOT BE OBSERVED UNLESS AN OBSERVER ENTERS OR RESIDES WITHIN. "THIS CONDITION WOULD BE SATISFIED IF OUR UNIVERSE WERE THE INTERIOR OF A BLACK HOLE EXISTING IN A BIGGER UNIVERSE," HE SAID. "BECAUSE EINSTEIN'S GENERAL THEORY OF RELATIVITY DOES NOT CHOOSE A TIME ORIENTATION, IF A BLACK HOLE CAN FORM FROM THE GRAVITATIONAL COLLAPSE OF MATTER THROUGH AN EVENT HORIZON IN THE FUTURE THEN THE REVERSE PROCESS IS ALSO POSSIBLE. SUCH A PROCESS WOULD DESCRIBE AN EXPLODING WHITE HOLE: MATTER EMERGING FROM AN EVENT HORIZON IN THE PAST, LIKE THE EXPANDING UNIVERSE." A WHITE HOLE IS CONNECTED TO A BLACK HOLE BY AN EINSTEIN-ROSEN BRIDGE (WORMHOLE) AND IS HYPOTHETICALLY THE TIME REVERSAL OF A BLACK HOLE. POPLAWSKI'S PAPER SUGGESTS THAT ALL ASTROPHYSICAL BLACK HOLES, NOT JUST SCHWARZSCHILD AND EINSTEIN-ROSEN BLACK HOLES, MAY HAVE EINSTEIN-ROSEN BRIDGES, EACH WITH A NEW UNIVERSE INSIDE THAT FORMED SIMULTANEOUSLY WITH THE BLACK HOLE. "FROM THAT IT FOLLOWS THAT OUR UNIVERSE COULD HAVE ITSELF FORMED FROM INSIDE A BLACK HOLE EXISTING INSIDE ANOTHER UNIVERSE," HE SAID. BY CONTINUING TO STUDY THE GRAVITATIONAL COLLAPSE OF A SPHERE OF DUST IN ISOTROPIC COORDINATES, AND BY APPLYING THE CURRENT RESEARCH TO OTHER TYPES OF BLACK HOLES, VIEWS WHERE THE UNIVERSE IS BORN FROM THE INTERIOR OF AN EINSTEIN-ROSEN BLACK HOLE COULD AVOID PROBLEMS SEEN BY SCIENTISTS WITH THE BIG BANG THEORY AND THE BLACK HOLE INFORMATION LOSS PROBLEM WHICH CLAIMS ALL INFORMATION ABOUT MATTER IS LOST AS IT GOES OVER THE EVENT HORIZON (IN TURN DEFYING THE LAWS OF QUANTUM PHYSICS). THIS MODEL IN ISOTROPIC COORDINATES OF THE UNIVERSE AS A BLACK HOLE COULD EXPLAIN THE ORIGIN OF COSMIC INFLATION, POPLAWSKI THEORIZES.COPYRIGHT SPACE DAILY URL :HTTP://WWW.SPACEDAILY.COM/REPORTS/OUR_UNIVERSE_AT_HOME_WITHIN_A_LARGER_UNIVERSE_999.HTML

22-04-10

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.

03-01-10

WAT WAS ER VOOR DE BIG BANG ?

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

03-04-09

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

25-01-09

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

30-12-08

What Can Swiss Cheese Teach us About Dark Energy?

Ali Vanderveld December 22, 2008About 10 years ago, scientists reached the astonishing conclusion that our universe is accelerating apart at ever-increasing speeds, stretching space and time itself like melted cheese. The force that's pushing the universe apart is still a mystery, which is precisely why it was dubbed "dark energy." But is dark energy really real? Is our universe really accelerating? These questions hang around in the mind of Ali Vanderveld, a post-doctoral cosmologist at JPL. Vanderveld and her colleagues recently published a paper in the journal Physical Review looking at how giant holes in our "Swiss-cheese-like" universe might make space look as if it's accelerating when it's really not. They concluded these holes, or voids, are not sufficient to explain away dark energy; nevertheless, Vanderveld says it's important to continue to question fundamental traits of the very space we live in. "Sometimes we take dark energy for granted," said Vanderveld. "But there are other theories that could explain why the universe appears to be moving apart at faster and faster speeds." Why do scientists think the universe is accelerating? A large part of the evidence comes from observations taken over the last decade or so of very distant, colossal star explosions called supernovae. JPL's Wide-Field and Planetary Camera 2 on NASA's Hubble Space Telescope contributed to this groundbreaking research. Astronomers had already figured out that space, since its inception about 13.7 billion years ago in a tremendous "Big Bang" explosion, is expanding. But they didn't know if this expansion was happening at a constant rate, and even speculated that it could be slowing down. By examining distant supernovae billions of light-years away, scientists could get a look at how the expansion of space behaves over time.The results were baffling. The more distant supernovae were dimmer than predicted, which would suggest they are farther away than previously believed. If they are farther away, then this means the space between us and the supernovae is expanding at ever-increasing speeds. Additional research has since pointed to an accelerating universe. A group of researchers from Fermi National Accelerator Laboratory in Batavia, Ill., recently invoked what's called the Swiss-cheese model of the universe to explain why these supernovae might appear to be moving faster away from us than they really are. The universe is made up of lumps of matter interspersed with giant holes, or voids, somewhat like Swiss cheese. In fact, last year, astronomers at the University of Minnesota, Twin Cities, reported finding the king of all known voids, spanning one billion light-years. In other words, it would take light -- which holds the title for fastest stuff in the universe -- one billion years to go from one side of the void to the other!The researchers at Fermi said these voids might lie between us and the supernovae being observed, acting like concave lenses to make the objects appear dimmer and farther than they really are. If so, then the supernova might not be accelerating away from us after all. Their theory claimed to provide a way in which dark energy might go poof.Vanderveld and her colleagues at Cornell University, Ithaca, N.Y., looked more closely at this theory and found a few "holes." The group at Fermi had assumed a bunch of voids would line up between us and the supernovae, but Vanderveld's group said, in reality, the voids would be distributed more randomly -- again like Swiss cheese. With this random distribution, the voids are not enough to explain away dark energy. "The lumpiness of the universe could still be tricking us into thinking it's accelerating," said Vanderveld. "But we did not find this to be the case with our best, current models of the universe."There is, however, one other freakish possibility that could mean a void is creating the illusion of an accelerating universe. If our solar system just happened to sit in the middle of a void, then that void would distort our observations. Said Vanderveld, "It's really hard to tell if we're in a void, but for the most part this possibility has been ruled out."Media contacts: Whitney Clavin 818-354-4673Jet Propulsion Laboratory, Pasadena, Calif.whitney.clavin@jpl.nasa.govCOPYRIGHT JPL URL : http://www.jpl.nasa.gov/news/features.cfm?feature=1988CompositionCosmos_550

21-11-08

Dark Matter Proof Found Over Antarctica?

Anne Minardfor National Geographic NewsNovember 19, 2008High-energy electrons captured over Antarctica could reveal the presence of a nearby but mysterious astrophysical object that's bombarding Earth with cosmic rays, researchers say. Or the electrons may be the long-awaited physical evidence of elusive dark matter. Either way, the unusual particles are exciting for astrophysicists, who say they could someday confirm or deny decades of unproven theories. "In the first case, we have now seen for the first time a nearby source of cosmic rays. Nobody's seen that before," said study co-author John Wefel, a physicist at Louisiana State University in Baton Rouge. "In the second case, we may be seeing something even more stupendous." Annihilation Signal Cosmic rays are not beams per se but are any protons, electrons, and other subatomic particles that careen toward Earth from a variety of sources, including the supernova explosions that mark the deaths of stars. Most of the cosmic electrons that reach Earth are low-energy, because the highest-energy ones fizzle the fastest and don't last long enough to get here. Capturing any electrons at all from the high end of the energy spectrum requires a sustained sampling effort. The authors of the new study flew a balloon-borne particle collector called the Advanced Thin Ionization Calorimeter (ATIC) over Antarctica. Circular winds at that latitude allow the balloon to stay aloft for up to 30 days at a time, capturing electrons and measuring their charges, energies, and trajectories. The team got a surprise: ATIC found inflated numbers of high-energy electrons that match the signal expected from the destruction of dark matter. The existence of dark matter has largely been inferred from its gravitational effects, such as the fact that most galaxies have enough mass to remain as well-defined objects despite having too little visible matter to account for the necessary gravity. A few exotic particles have been suggested as dark matter ingredients. One of these, named the Kaluza-Klein particle, is predicted to have the same mass as 550 to 650 protons. When these theoretical Kaluza-Klein particles collide and annihilate, they're expected to produce electrons with energies between 550 and 650 gigaelectron volts, or GeV. One GeV is roughly the energy locked up in the mass of a single proton, according to Einstein's famous formula E=mc2. At 620 GeV, the odd energy spike in the Antarctic electrons falls within that range, the authors report in this week's issue of the journal Nature. Mystery Object As an alternative theory, the authors say, a nearby astrophysical object could be churning out high-energy electrons that are reaching Earth. Possibilities include a pulsar, which is the highly magnetic, rotating remnant of a collapsed star, or a microquasar, the luminous, energetic collection of material orbiting a small black hole. Astrophysicist Okkie de Jager, of North-West University in Potchefstroom, South Africa, and colleagues announced the discovery in April that two pulsars—Geminga and B0656+14—are local sources of high-energy cosmic rays. These pulsars could be producing the newly discovered electrons, de Jager said. "I would put my money on a local source, simply because we do have the smoking gun to this effect," said de Jager, who was not involved in the new study. Yousaf Butt, an astrophysicist at the National Academy of Sciences, wrote a commentary on the work also appearing in Nature. "Let's not forget that a completely new type of astrophysical object could also produce the detected electron excess," Butt said. "After all, pulsars were discovered only in 1967, and until 1992 we were blissfully unaware of microquasars." For its high-energy electrons to reach Earth, such an object would need to be close, astrophysically speaking—within about 3,000 light-years of Earth. Undecided Study co-author Wefel said his research team doesn't favor either theory just yet. "We're sort of stuck in between the two. We can't decide." No known object precisely matches the data on hand, and the results aren't conclusive for the detection of dark matter, he noted. "We just do not have enough events to prove they're responsible," he said, referring to the Kaluza-Klein particles. "It's suggestive but it's not proven." Further sampling is key, he said, but funding has not been renewed for his team to continue using ATIC over Antarctica. Giant neutrino telescopes like IceCube, A University of Wisconsin-led project built at the South Pole, could find more dark matter clues. And an instrument called CALorimetric Electron Telescope, or CALET, is now being designed in Japan with the hope that it will join the International Space Station in 2013. CALET would collect electrons over Earth for at least 1,000 days, as opposed to ATIC's 30. Fermi, NASA's gamma-ray space telescope formerly known as GLAST, is also capable of measuring an electron spectrum. And the European Union's Cherenkov Telescope Array, now under development, may be able to locate dark matter hot spots in the universe. Finally, when it's running smoothly, the Large Hadron Collider in Europe will function in part as an experimental dark matter factory, producing collisions at 14,000 GeV that could help shed light on dark matter's exotic particles. COPYRIGHT : http://news.nationalgeographic.com/news/bigphotos/44410460.html

03-08-08

Supervoids and superclusters point to dark dark energy

BY DR EMILY BALDWIN ASTRONOMY NOWPosted: July 30, 2008By studying regions of space with an above and below average concentration of galaxies – superclusters and supervoids, respectively – a team of astronomers have found direct evidence for the existence of dark energy.The nature of dark energy is one of the biggest puzzles of modern science, but it is thought to work against the tendency of gravity to pull galaxies together, causing the Universe’s expansion to speed up. Impressively, astronomers from the University of Hawaii Institute for Astronomy were able to catch this elusive dark energy in action as it stretches out the largest known structures in the Universe: supervoids and superclusters, vast regions of space half a billion light years across, containing either a deficit or surplus of galaxies, brought about by density fluctuations in the early Universe. The key to the team’s success was to measure the subtle imprints that superclusters and supervoids leave in microwaves that pass through them. But this signal is extremely difficult to detect since ripples in the primordial cosmic microwave background radiation (CMB) – the faint hiss of microwaves left over from the big bang – are larger than the imprints of individual superclusters and supervoids. Therefore, to extract a signal, the team compared an existing database of galaxies with a map of the CMB and averaged together local regions around the 50 largest supervoids and the 50 largest superclusters from a collection of bright galaxies drawn from the Sloan Digital Sky Survey. As expected, the microwaves were slightly stronger if they had passed through a supercluster, and marginally weaker if they had passed through a supervoid. “When a microwave enters a supercluster, it gains some gravitational energy, and therefore vibrates slightly faster,” explains Szapudi. “Later, as it leaves the supercluster, it should lose exactly the same amount of energy. But if dark energy causes the Universe to stretch out at a faster rate, the supercluster flattens out in the half billion years it takes the microwave to cross it. Thus, the wave gets to keep some of the energy it gained as it entered the supercluster.”Essentially, the dark energy is giving the microwaves a memory of where they’ve been. “With this method, for the first time we can actually see what supervoids and superclusters do to microwaves passing through them,” says Benjamin Granett, first author on the paper describing the results, which will appear in a forthcoming issue of the Astrophysical Journal Letters. “We plan to follow up with one of the coldest regions of the CMB, the ‘Cold Spot’, to determine whether it is due to a large void as hypothesised recently,” reveals Szapudi. The so-called cold spot is in fact only a few millionths of a degree colder than its surrounds, but some scientists think that it may be caused by a huge hole devoid of nearly all matter, perhaps as large as a thousand light million years in size.Copyright http://astronomynow.com/080730Supervoidsandsuperclusterspointtodarkenergy.html dark energy

06-07-08

Destiny, the Dark Energy Space Telescope

Destiny, the Dark Energy Space Telescope, is lead by Tod Lauer of the National Optical Astronomy Observatory, based in Tucson, Arizona. If launched, Destiny's 1.65-meter near-infrared telescope will detect more than 3,000 Type Ia supernovae over the two-year primary mission, followed by a year-long survey of 1,000 square-degrees of the sky to measure how the large-scale distribution of matter in the universe has evolved since the Big Bang. The data from these two surveys will have 10 times better sensitivity than current ground-based projects to explore the properties of dark energy.The spacecraft will use a specialized instrument known as a grism to simultaneously acquire the spectra of all objects in its field of view. The spacecraft itself will orbit the Sun at the second Lagrangian point, where the gravitational forces of the Sun, Earth, and Moon balance one another.copyright http://universe.nasa.gov/program/probes/destiny.htmldestiny