17-03-11

NASA Prepares Antimatter-Hunting Detector for Space Shuttle Launch

 

16 March 2011

 

 

cosmologyn,dark matter,AMS,Space Shuttle,ISS

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


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

 

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

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

 


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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."

 


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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

 

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

 


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

 

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

 

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

 

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


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


The two Magellanic are each about ten times larger.


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


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


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


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


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

 

 

 

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

 

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

 

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

 

12-11-10

Hubble Provides Most Detailed Dark Matter Map Yet

 

11th November 2010

 

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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).

 

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

 

18-08-10

Phantom Universe - Next Biggest Mystery

Analysis by Ray Villard

 

Mon Aug 16, 2010 04:27 PM ET

 

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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.

 

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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.

 

Copyright


http://news.discovery.com/space/phantom-universe-next-big...

 

 

 

 

 

 

 

 

14-06-10

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

11-05-10

X-ray Discovery Points to Location of Missing Matter

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

02-05-10

Donkere materie in kaart gebracht

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

30-04-10

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

27-04-10

Cosmic Dark Matter Clumps Into Cigar Shapes

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

07-02-10

Distant Galaxies Unlock New Secrets of Dark Matter

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

22-12-09

Mystery Swirls Around 'Dark Stars'

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

26-09-09

A Prototype Detector for Dark Matter in the Milky Way 25092009

Dark-Matter-DetectorIt doesn't emit electromagnetic radiation and no one really knows what it is, but that hasn't stopped a team of European researchers from developing a device which scientists will use to detect and determine the nature of the dark matter that makes up 1/4 of the mass of our universe.The researchers from the University of Zaragoza (UNIZAR) and the Institut d'Astrophysique Spatiale (IAS, in France), made assumptions about the nature of dark matter based on theoretical studies, and developed device called a "scintillating bolometer" to detect the result of interaction of dark matter with material inside the detector."One of the biggest challenges in Physics today is to discover the true nature of dark matter, which cannot be directly observed – even though it seems to make up one-quarter of the matter of the Universe. So we have to attempt to detect it using prototypes such as the one we have developed", Eduardo García Abancéns, a researcher from the UNIZAR's Laboratory of Nuclear Physics and Astroparticles, tells SINC.García Abancéns is one of the scientists working on the ROSEBUD project (an acronym for Rare Objects SEarch with Bolometers UndergrounD), an international collaborative initiative between the Institut d'Astrophysique Spatiale (CNRS-University of Paris-South, in France) and the University of Zaragoza, which is focusing on hunting for dark matter in the Milky Way.The scientists have been working for the past decade on this mission at the Canfranc Underground Laboratory, in Huesca, where they have developed various cryogenic detectors (which operate at temperatures close to absolute zero: ?273.15 °C). The latest is a "scintillating bolometer", a 46-gram device that, in this case, contains a crystal "scintillator", made up of bismuth, germinate and oxygen (BGO: Bi4Ge3O12), which acts as a dark matter detector.Naturally, to build any type of dark matter detector, the researchers had to make some assumptions about the nature of the dark matter itself. The detection technique developed by the researchers is based on a number of theoretical studies which point to particles called WIMPs (Weakly Interacting Massive Particles) as the main constituent of dark matter."This detection technique is based on the simultaneous measurement of the light and heat produced by the interaction between the detector and the hypothetical WIMPs which, according to various theoretical models, explain the existence of dark matter", explains García Abancéns.The researcher explains that the difference in the scintillation of the various particles enables this method to differentiate between the signals that the WIMPs would produce and others produced by various elements of background radiation (such as alpha, beta or gamma particles).In order to measure the miniscule amount of heat produced, the detector must be cooled to temperatures close to absolute zero, and a cryogenic facility, reinforced with lead and polyethylene bricks and protected from cosmic radiation as it housed under the Tobazo mountain, has been installed at the Canfranc underground laboratory."The new scintillating bolometer has performed excellently, proving its viability as a detector in experiments to look for dark matter, and also as a gamma spectrometer (a device that measures this type of radiation) to monitor background radiation in these experiments", says García Abancéns.The scintillating bolometer is currently at the Orsay University Centre in France, where the team is working to optimise the device's light gathering, and carrying out trials with other BGO crystals.This study, published recently in the journal Optical Materials, is part of the European EURECA project (European Underground Rare Event Calorimeter Array). This initiative, in which 16 European institutions are taking part (including the University of Zaragoza and the IAS), aims to construct a one-tonne cryogenic detector and use it over the next decade to hunt for the dark matter of the Universe.COPYRIGHT http://www.universetoday.com and Source: FECYT (Spain) - http://www.fecyt.es/fecyt/home.do

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

29-12-08

Astronomers Aim to Grasp Mysterious Dark Matter

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

17-12-08

Dark Energy Found Stifling Growth in the Universe

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

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

21-09-08

Astronomers Discover Most Dark Matter-Dominated Galaxy in Universe

dark matterPublished: September 18, 2008New Haven, Conn. — A team led by a Yale University astronomer has discovered the least luminous, most dark matter-filled galaxy known to exist. The galaxy, called Segue 1, is one of about two dozen small satellite galaxies orbiting our own Milky Way galaxy. The ultra-faint galaxy is a billion times less bright than the Milky Way, according to the team’s results, to be published in an upcoming issue of The Astrophysical Journal (ApJ). But despite its small number of visible stars, Segue 1 is nearly a thousand times more massive than it appears, meaning most of its mass must come from dark matter.“I’m excited about this object,” said Marla Geha, an assistant professor of astronomy at Yale and the paper’s lead author. “Segue 1 is the most extreme example of a galaxy that contains only a few hundred stars, yet has a relatively large mass.”Geha, along with her colleague Josh Simon at the California Institute of Technology, has observed about half of the dwarf satellite galaxies that orbit the Milky Way. These objects are so faint and contain so few stars that at first they were thought to be globular clusters – tightly bound star clusters that also orbit our host galaxy. But by analyzing the light coming from the objects using the Keck telescope in Hawaii, Geha and Simon showed that these objects are actually galaxies themselves, albeit very dim ones.Looking only at the light emitted by these ultra-faint galaxies, Geha and her colleagues expected them to have correspondingly low masses. Instead, they discovered that they are between 100 and 1000 times more massive than they appear. Invisible dark matter, she said, must account for the difference.Although dark matter doesn’t emit or absorb light, scientists can measure its gravitational effect on ordinary matter and believe it makes up about 85 percent of the total mass in the universe. Finding ultra-faint galaxies like Segue 1, which is so rife with dark matter, provides clues as to how galaxies form and evolve, especially at the smallest scales. “These dwarf galaxies tell us a great deal about galaxy formation,” Geha said. “For example, different theories about how galaxies form predict different numbers of dwarf galaxies versus large galaxies. So just comparing numbers is significant.” It’s only recently that astronomers have discovered just how prevalent these dwarf satellite galaxies are, thanks to projects like the Sloan Digital Sky Survey, which imaged large areas of the nighttime sky in greater detail than ever before. In the past two years alone, the number of known dwarf galaxies orbiting the Milky Way has doubled from the dozen or so brightest that were discovered during the first half of the twentieth century. Geha predicts astronomers will find even more as they continue to sift through new data. “The galaxies I now consider bright used to be the least luminous ones we knew about,” she said. “It’s a totally new regime. This is a story that’s just unfolding.”The authors of the paper are Marla Geha (Yale University), Beth Willman (Harvard-Smithsonian Center for Astrophysics), Joshua D. Simon (California Institute of Technology), Louis E. Strigari (University of California, Irvine), Evan N. Kirby (University of California, Santa Cruz and Lick Observatory), David R. Law (California Institute of Technology) and Jay Strader (Harvard-Smithsonian Center for Astrophysics).PRESS CONTACT: Suzanne Taylor Muzzin 203-432-8555COPYRIGHT : SCIENCE AND ENGINEERING URL http://www.opa.yale.edu/news/article.aspx?id=6037

02-09-08

A Clash of Clusters Provides New Clue to Dark Matter

A powerful collision of galaxy clusters has been captured by NASA’s Hubble Space Telescope and Chandra X-ray Observatory. The observations of the cluster known as MACS J0025.4-1222 indicate that a titanic collision has separated the dark from ordinary matter and provide an independent confirmation of a similar effect detected previously in a target dubbed the Bullet Cluster. These new results show that the Bullet Cluster is not an anomalous case.Copyright : http://hubblesite.org/newscenter/archive/releases/2008/32/blogjpeg

28-08-08

XMM-Newton’s massive discovery - 25 August 2008

ESA’s orbiting X-ray observatory XMM-Newton has discovered the most massive cluster of galaxies seen in the distant Universe until now. The galaxy cluster is so big that there can only be a handful of them at that distance, making this a rare catch indeed. The discovery confirms the existence of dark energy.The newly-discovered monster, known only by the catalogue number 2XMM J083026+524133, is estimated to contain as much mass as a thousand large galaxies. Much of it is in the form of 100-million-degree hot gas. It was first observed by chance as XMM-Newton was studying another celestial object and 2XMM J083026+524133 was placed in a catalogue for a future follow-up. Georg Lamer, Astrophysikalisches Institut Potsdam, Germany, and a team of astronomers discovered the record-breaking cluster as they were performing a systematic analysis of the catalogue. Based on 3500 observations performed with XMM-Newton's European Photon Imaging Camera (EPIC) covering about 1% of the entire sky, the catalogue contains more than 190 000 individual X-ray sources. The team were looking for extended patches of X-rays that could either be nearby galaxies or distant clusters of galaxies. J083026+524133 stood out because it was so bright. While checking visual images from the Sloan Digital Sky Survey, the team could not find any obvious nearby galaxy in that location. So they turned to the Large Binocular Telescope in Arizona and took a deep exposure.Sure enough, they found a cluster of galaxies. So the team calculated a distance of 7.7 thousand million light-years and the cluster's mass using the XMM-Newton data. This was not a surprise because XMM-Newton is sensitive enough to routinely find galaxy clusters at this distance. The surprise was that the cluster contains a thousand times the mass of our own galaxy, the Milky Way.2XMM J083026+524133“Such massive galaxy clusters are thought to be rare objects in the distant Universe. They can be used to test cosmological theories,” says Lamer. Indeed, the very presence of this cluster confirms the existence of a mysterious component of the Universe called dark energy. No one knows what dark energy is, but it is causing the expansion of the Universe to accelerate. This hampers the growth of massive galaxy clusters in more recent times, indicating that they must have formed earlier in the Universe. “The existence of the cluster can only be explained with dark energy,” says Lamer. Yet he does not expect to find more of them in the XMM-Newton catalogue. “According to the current cosmological theories, we should only expect to find this one cluster in the 1% of sky that we have searched,” says Lamer. In other words, the team have found a cosmic ‘needle in a haystack’.Notes for editors:‘2XMM J083026+524133: The most X-ray luminous cluster at redshift 1’ by G. Lamer, M. Hoeft, J. Kohnert, A. Schwope, and J. Storm will be published in a forthcoming issue of the journal Astronomy & Astrophysics. The XMM-Newton science teams are based in several European and US institutes, grouped into three instrument teams and the XMM-Newton Survey Science Centre (SSC). Science operations are managed at ESA’s European Space Astronomy Centre (ESAC), at Villanueva de la Cañada near Madrid, Spain. Spacecraft operations are managed at ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany.Copyright : ESA PORTAL http://www.esa.int/esaCP/SEMY70XIPIF_index_0.htmlXMM NEWTON

18-05-08

WORLD WIDE TELESCOPE ITEM : Biggest 'Zoom Lens' in Space Takes Hubble Deeper into the Universe

January 7, 2003 12:20 PM (EST) The Advanced Camera for Surveys aboard NASA's Hubble Space Telescope has used a natural "zoom lens" in space to boost its view of the distant universe. Besides offering an unprecedented and dramatic new view of the cosmos, the results promise to shed light on galaxy evolution and dark matter in space.Hubble peered straight through the center of one of the most massive galaxy clusters known, called Abell 1689. This required that Hubble gaze at the distant cluster, located 2.2 billion light-years away, for over 13 hours. The gravity of the cluster's trillion stars — plus dark matter — acts as a 2-million-light-year-wide "lens" in space. This "gravitational lens" bends and magnifies the light of galaxies located far behind it. The Advanced Camera's IMAX movie-quality sharpness, combined with the behemoth lens, reveals remote galaxies previously beyond even Hubble's reach. A few may be twice as faint as those photographed in the Hubble Deep Field, which previously pushed the telescope to its sensitivity limits. Though much more analysis is needed, Hubble astronomers speculate that some of the faintest objects in the picture are probably over 13 billion light-years away (redshift value 6).In the image hundreds of galaxies many billions of light-years away are smeared by the gravitational bending of light into a spider-web tracing of blue and red arcs of light. Though gravitational lensing has been studied previously with Hubble and ground-based telescopes, this phenomenon has never been seen before in such detail. The ACS picture reveals 10 times more arcs than would be seen by a ground-based telescope. The ACS is 5 times more sensitive and provides pictures that are twice as sharp as the previous work-horse Hubble cameras. So it can see the very faintest arcs with greater clarity. The picture presents an immense jigsaw puzzle for Hubble astronomers to spend months untangling. Interspersed with the foreground cluster are thousands of galaxies, which are lensed images of the galaxies in the background universe. Detailed analysis of the images promises to shed light on the mystery of dark matter. Dark matter is an invisible form of matter. It is the source of most of the gravity in the universe because it is much more abundant than the "normal matter" that makes up planets, stars and galaxies. The lensing allows astronomers to map the distribution of dark matter in galaxy clusters. This should offer new clues to the nature of dark matter. By studying the lensed distant galaxies, astronomers expect to better trace the history of star formation in the universe, over the past 13 billion years. The picture is an exquisite demonstration of Albert Einstein's prediction that gravity warps space and therefore distorts a beam of light, like a rippled shower curtain. Though Einstein realized this effect would happen in space, he thought it could never be observed from Earth. Though individual stars lens background light, the deflection was too small to ever be seen from Earth. When the laws of relativity were formulated in the early 20th century, scientists did not know that stars were organized into galaxies beyond our own Milky Way. Great clusters of galaxies are massive enough to warp space and deflect light in a way that is detectable from Earth. The Abell cluster is the ideal target because it is so massive. The more massive a cluster, the larger the effects of gravitational lensing. Copyright http://hubblesite.org/newscenter/archive/releases/2003/01/text/MICROSOFT WORLD WIDE TELESCOPE HAS A GUIDED TOUR TO THESE IMAGES AND AUDIO INFORMATION GIVEN BY MIKE GLADDERS AT THE UNIVERSITY OF CHICAGO LAST DECEMBER 2007. PLEASE DOWNLOAD THE VERY INTERESTING SOFTWARE OF MICROSOFT AND LOOK FOR THIS ITEM...IT'S FANTASTIC SCIENCE !!!gravitational lens

26-02-08

How can Glast help us find dark energy and dark matter?

Here is the answer from David Band ; nasa project Glast.GLAST may see gamma-ray line emission from the decay or annihilation of the sub-atomic particle(s) that make up the dark matter. In some theories the decay or annihilation of these particles emits gamma rays of a specific energy, and should occur in regions where many of these particles are clustered together.This clustering will result from the gravitational attraction of the dark matter.Also, gamma ray emission from regular matter will be greater in regions where the dark matter has caused matter to accumulate.glastI am not aware of any GLAST observations that will have a direct connection with dark energy. But I would not be surprised if someone found one!