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


December 10, 2010 by Lisa Zyga Enlarge






(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.



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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


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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)
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Radio Astronomers Develop New Technique for Studying Dark Energy


Dark Energy and Dark Matter Might Not Exist, Scientists Allege

By Clara MoskowitzSPACE.com Senior Writerposted: 13 June 201007:01 pm ET Dark matter and dark energy are two of the most mind-boggling ingredients in the universe. Ever since these concepts were first proposed, some astronomers have worked feverishly to figure out what each thing is, while other astronomers have tried to prove they don't exist, in hopes of restoring the universe to the more understandable place many would like it to be.A new look at the data from one of the telescopes used to establish the existence of this strange stuff is causing some scientists to question whether theyreally exist at all. Yet other experts are holding firm to the idea that, whether we like it or not, the "dark side" of the universe is here to stay.Dark matter is a proposed form of matter that could make up 22 percent of the universe's mass-energy budget, vastly outweighing all the normal matter, like stars and galaxies. Astronomers can't observe dark matter directly, but they think it's there because of the gravitational pull it seems to exert on everything else. Without dark matter, the thinking goes, galaxies would fly apart.Ads by GoogleJesus: Hoax or Reality?Discover the Evidence From Scholars About Jesus' Claims to be God www.Y-Jesus.com/GodWhy is Brazil Hot What the Banks are not saying What the Banks are investing in www.greenwood-management.comAs if that weren't weird enough, scientists think another 74 percent of themass-energy budget could be made of some strange quantity called dark energy. This force is thought to be responsible for the accelerating pace of the expansion of the universe. (For those keeping track, that would leave only a measly 4 percent of the universe composed of normal matter.)Some cosmic backgroundOne of the prime ways researchers tally how much these components contribute to the overall makeup of the universe is by measuring a dim glow of light pervading space that is thought to be left over from the Big Bang. The most detailed measurements yet taken of this radiation, which is called the cosmic microwave background (CMB), come from a spacecraft dubbed the Wilkinson Microwave Anisotropy Probe (WMAP)."It's such an important thing — the microwave background," said astrophysicist Tom Shanks of Durham University in England. "All the results in dark energy and dark matter in cosmology hang on it, and that's why I'm interested in checking the results."Recently Shanks and his graduate student Utane Sawangwit went back to examine the WMAP data and used a different method to calibrate how much smoothing,or blurring, the telescope was causing to its images. This smoothing is an expected affect, akin to the way Earth's atmosphere blurs stars' light so they twinkle.Instead of using Jupiter as a calibration source, the way the WMAP team did, Shanks and Sawangwit used distant astronomical objects in the WMAP data itself that were emitting radio light."When we checked radio sources in the WMAP background, we found more smoothing than the WMAP team expected," Shanks told SPACE.com. "That would have big implications for cosmology if we were proven right."If this smoothing error is larger than thought, it could indicate that fluctuations measured in the intensity of the CMB radiation are actually smaller than they originally appeared. The size of these fluctuations is a key parameter used to support the existence of dark matter and dark energy. With smaller ripples, there would be no need to invoke exotic concepts like dark matter and dark energy to explain the CMB observations, Shanks said.The researchers will report their findings in an upcoming issue of the journal Monthly Notices of the Royal Astronomical Society.Others not so sure !Yet other astronomers, particularly those who first analyzed the WMAP results, remain unconvinced. "The WMAP team has carried out extensive checks and we unequivocally stand by our results," said WMAP principal investigator Charles Bennett of Johns Hopkins University in Baltimore, Md.The WMAP researchers take issue with Sawangwit and Shanks' use of dim, far-away radio sources to calculate the telescope's smoothing error."These are weak sources, so many of them must be averaged together to obtain useful measurements. None of them move with respect to the CMB," said WMAP team member Mark Halpern of the University of British Columbia. "This method is inferior to our main approach."Plus, Halpern said he and his colleagues had identified an error the other team made in failing to account for the confusing contribution of the CMB ripples themselves."We can obtain the Shanks result by omitting the step that properly accounts for the background confusion, but this step is necessary," Bennett explained.Back in this corner ...Yet Shanks said he's aware of these objections and stands by his calculations. "We don't think that's an issue," he said.Ultimately, Shanks hopes future measurements of the microwave background radiation from new telescopes will help clear up the issue.The European Space Agency's Planck spacecraft, launched into orbit in 2009, is currently taking new, even more detailed observations of the CMB. "I'm very interested to see what Planck gets in terms of its results," Shanks said. "And of course we will be there to try and keep everybody as honest aspossible. We're hoping we can use our methods in the same way to check their beam profile that they ultimately come up with."copyright space.com URLhttp://www.space.com/scienceastronomy/dark-matter-dark-energy-question-100613.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+spaceheadlines+%28SPACE.com+Headline+Feed%29CMB thumbnail


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


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.


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


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


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


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


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


Huge lenses to observe cosmic dark energy

UK astronomers, as part of an international team, have reached a milestone in the construction of one of the largest ever cameras to detect the mysterious Dark Energy component of the Universe. The pieces of glass for the five unique lenses of the camera have been shipped from the US to France to be shaped and polished into their final form. The largest of the five lenses is one metre in diameter, making it one of the largest in the world.Each milestone in the completion of this sophisticated camera brings us closer to detecting the mysterious and invisible matter that cosmologists estimate makes up around three quarters of our Universe and is driving its accelerating expansion. Observations suggest that roughly 4% of the Universe is made up from ordinary matter and 22% from Dark Matter; this leaves 74% unaccounted for - the so-called Dark Energy.The Dark Energy Survey (DES) camera will map 300 million galaxies using the Blanco 4-meter telescope - a large telescope with new advanced optics at Chile’s Cerro Tololo Inter-American Observatory.The vast DES galaxy map will enable the astronomers to measure the Dark Energy far more precisely than current observations. Prof. Ofer Lahav, head of the UCL Astrophysics Group, who also leads the UK DES Consortium, commented "Dark Energy is one of the biggest puzzles in the whole of Physics, going back to a concept proposed by Einstein 90 years ago. The DES observations will tell us if Einstein was right or if we need a major shift in our understanding of the universe.”The glass for the five lenses was manufactured in the US before being shipped to France where the lenses will be polished to a smoothness level of one millionth of a centimetre.Dr Peter Doel of the Optical Science Laboratory at UCL said, "The polishing and assembly of the five DES lenses will be a major technological achievement, producing one of the largest cameras on Earth.”This level of polishing across such large lenses is far more demanding than for normal eye glasses. The lenses will then be sent to the Optical Science Laboratory at UCL in London for assembly into the camera and from there to the telescope in Chile, where observations will start in 2011 and will continue until 2016.The Science and Technology Facilities Council (STFC) is providing support for the Dark Energy Survey (DES) collaboration, which involves over 100 scientists from the US, UK, Spain and Brazil. The UK consortium includes members from UCL (University College London), Portsmouth, Cambridge, Edinburgh and Sussex universities.The latest milestone was announced by astronomers from UCL and the US Fermilab National Accelerator Laboratory at a conference on optical instrumentation held at Marseille France, on 23 June 2008.The DES Director, Prof. John Peoples of Fermilab, commented "The DES Team is thrilled that this long and technically demanding step in the construction of the camera has begun and we congratulate the STFC for making it possible to meet this milestone on schedule."Professor John Womersley, the Director of Programmes at STFC, added, “We are delighted that the UK is taking an important role in this innovative project which will help us understand one of the deepest mysteries of the universe."Copyright http://allesoversterrenkunde.nl/content.shtml?http://allesoversterrenkunde.nl/cgi-bin/scripts/db.cgi?db=nieuws&ww=on&ID=2492&view_records=1 and http://www.scitech.ac.uk/PMC/PRel/STFC/LensesCDE.aspxdark energy


Donkere energie : een zoektocht gedurende de komende 10 jaar

In de komende 10 jaar zullen we meer te weten komen over donkere energie.We hebben reeds in deze weblog gesproken over nauwkeuriger metingen die men zal doen. Het zal een boeiende ontdekkingstocht worden. Is donkere energie echt donker, losgekoppeld van materie en andere quantum velden ? Zijn er nieuwe constanten te vinden ?De toekomst zal het uitwijzen.darkmatter