New from Space: Simulations and X-Rays Point to Dark Matter

center_universe2The cosmic hunt for dark matter has been turning up some interesting clues of late. And during the month of June, two key hints came along that might provide answers; specifically simulations that look at the “local Universe” from the Big Bang to the present day and recent studies involving galaxy clusters. In both cases, the observations made point towards the existence of Dark Matter – the mysterious substance believed to make up 85 per cent of the mass of the Universe.

In the former case, the clues are the result of new supercomputer simulations that show the evolution of our “local Universe” from the Big Bang to the present day. Physicists at Durham University, who are leading the research, say their simulations could improve understanding of dark matter due to the fact that they believe that clumps of the mysterious substance – or halos – emerged from the early Universe, trapping intergalactic gas and thereby becoming the birthplaces of galaxies.

universe_expansionCosmological theory predicts that our own cosmic neighborhood should be teeming with millions of small halos, but only a few dozen small galaxies have been observed around the Milky Way. Professor Carlos Frenk, Director of Durham University’s Institute for Computational Cosmology, said:

I’ve been losing sleep over this for the last 30 years… Dark matter is the key to everything we know about galaxies, but we still don’t know its exact nature. Understanding how galaxies formed holds the key to the dark matter mystery… We know there can’t be a galaxy in every halo. The question is: ‘Why not?’.

The Durham researchers believe their simulations answer this question, showing how and why millions of halos around our galaxy and neighboring Andromeda failed to produce galaxies. They say the gas that would have made the galaxy was sterilized by the heat from the first stars that formed in the Universe and was prevented from cooling and turning into stars. However, a few halos managed to bypass this cosmic furnace by growing early and fast enough to hold on to their gas and eventually form galaxies.

dark_matterThe findings were presented at the Royal Astronomical Society’s National Astronomy Meeting in Portsmouth on Thursday, June 26. The work was funded by the UK’s Science and Technology Facilities Council (STFC) and the European Research Council. Professor Frenk, who received the Royal Astronomical Society’s top award, the Gold Medal for Astronomy, added:

We have learned that most dark matter halos are quite different from the ‘chosen few’ that are lit up by starlight. Thanks to our simulations we know that if our theories of dark matter are correct then the Universe around us should be full of halos that failed to make a galaxy. Perhaps astronomers will one day figure out a way to find them.

Lead researcher Dr Till Sawala, in the Institute for Computational Cosmology, at Durham University, said the research was the first to simulate the evolution of our “Local Group” of galaxies, including the Milky Way, Andromeda, their satellites and several isolated small galaxies, in its entirety. Dr Sawala said:

What we’ve seen in our simulations is a cosmic own goal. We already knew that the first generation of stars emitted intense radiation, heating intergalactic gas to temperatures hotter than the surface of the sun. After that, the gas is so hot that further star formation gets a lot more difficult, leaving halos with little chance to form galaxies. We were able to show that the cosmic heating was not simply a lottery with a few lucky winners. Instead, it was a rigorous selection process and only halos that grew fast enough were fit for galaxy formation.

darkmatter1The close-up look at the Local Group is part of the larger EAGLE project currently being undertaken by cosmologists at Durham University and the University of Leiden in the Netherlands. EAGLE is one of the first attempts to simulate from the beginning the formation of galaxies in a representative volume of the Universe. By peering into the virtual Universe, the researchers find galaxies that look remarkably like our own, surrounded by countless dark matter halos, only a small fraction of which contain galaxies.

The research is part of a program being conducted by the Virgo Consortium for supercomputer simulations, an international collaboration led by Durham University with partners in the UK, Germany, Holland, China and Canada. The new results on the Local Group involve, in addition to Durham University researchers, collaborators in the Universities of Victoria (Canada), Leiden (Holland), Antwerp (Belgium) and the Max Planck Institute for Astrophysics (Germany).

ESO2In the latter case, astronomers using ESA and NASA high-energy observatories have discovered another possible hint by studying galaxy clusters, the largest cosmic assemblies of matter bound together by gravity. Galaxy clusters not only contain hundreds of galaxies, but also a huge amount of hot gas filling the space between them. The gas is mainly hydrogen and, at over 10 million degrees celsius, is hot enough to emit X-rays. Traces of other elements contribute additional X-ray ‘lines’ at specific wavelengths.

Examining observations by ESA’s XMM-Newton and NASA’s Chandra spaceborne telescopes of these characteristic lines in 73 galaxy clusters, astronomers stumbled on an intriguing faint line at a wavelength where none had been seen before. The astronomers suggest that the emission may be created by the decay of an exotic type of subatomic particle known as a ‘sterile neutrino’, which is predicted but not yet detected.

dark_matter_blackholeOrdinary neutrinos are very low-mass particles that interact only rarely with matter via the so-called weak nuclear force as well as via gravity. Sterile neutrinos are thought to interact with ordinary matter through gravity alone, making them a possible candidate as dark matter. As Dr Esra Bulbul – from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA, and lead author of the paper discussing the results – put it:

If this strange signal had been caused by a known element present in the gas, it should have left other signals in the X-ray light at other well-known wavelengths, but none of these were recorded. So we had to look for an explanation beyond the realm of known, ordinary matter… If the interpretation of our new observations is correct, at least part of the dark matter in galaxy clusters could consist of sterile neutrinos.

The surveyed galaxy clusters lie at a wide range of distances, from more than a hundred million light-years to a few billion light-years away. The mysterious, faint signal was found by combining multiple observations of the clusters, as well as in an individual image of the Perseus cluster, a massive structure in our cosmic neighborhood.

The supermassive black hole at the center of the Milky Way galaxy.The implications of this discovery may be far-reaching, but the researchers are being cautious. Further observations with XMM-Newton, Chandra and other high-energy telescopes of more clusters are needed before the connection to dark matter can be confirmed. Norbert Schartel, ESA’s XMM-Newton Project Scientist, commented:

The discovery of these curious X-rays was possible thanks to the large XMM-Newton archive, and to the observatory’s ability to collect lots of X-rays at different wavelengths, leading to this previously undiscovered line. It would be extremely exciting to confirm that XMM-Newton helped us find the first direct sign of dark matter. We aren’t quite there yet, but we’re certainly going to learn a lot about the content of our bizarre Universe while getting there.

Much like the Higgs Boson, the existence of Dark Matter was first theorized as a way of explaining how the universe appears to have mass that we cannot see. But by looking at indirect evidence, such as the gravitational influence it has on the movements and appearance of other objects in the Universe, scientists hope to one day confirm its existence. Beyond that, there is the mystery of “Dark Energy”, the hypothetical form of energy that permeates all of space and is believed to be behind accelerations in the expansion of the universe.

As with the discovery of the Higgs Boson and the Standard Model of particle physics, detecting these two invisible forces will at last confirm that the Big Bang and Cosmological theory are scientific fact – and not just working theories. When that happens, the dream of humanity finally being able to understand the universe (at both the atomic and macro level) may finally become a reality!

Source: sciencedaily.com, (2)

News From Space: Cosmic Inflation and Dark Matter

big bang_blackholeHello again! In another attempt to cover events that built up while I was away, here are some stories that took place back in March and early April of this year, and which may prove to be some of the greatest scientific finds of the year. In fact, they may prove to be some of the greatest scientific finds in recent history, as they may help to answer the most fundamental questions of all – namely, what is the universe made of, and how did it come to exist?

First up, in a development that can only be described as cosmic in nature (pun intended), back in March, astrophysicists at the Harvard-Smithsonian Center announced the first-ever observation of gravitational waves. This discovery, which is the first direct evidence of the Big Bang, is comparable to significance to CERN’s confirmation of the Higgs boson in 2012. And there is already talk about a Nobel Prize for the Harvard crew because of their discovery.

big_bangThis theory, which states that the entire universe sprung into existence from a tiny spot in the universe some 13.8 billion years ago, has remained the scientific consensus for almost a century. But until now, scientists have had little beyond theory and observations to back it up. As the name would suggest, gravitational waves are basically ripples in spacetime that have been propagating outward from the center of the universe ever since the Big Bang took place.

Originally predicted as part of Einstein’s General Theory of Relativity in 1916, these waves are believed to have existed since a trillionth of a trillionth of a trillionth of a second after the Big Bang took place, and have been propagating outward for roughly 14 billion years. The theory also predicts that, if we can detect some gravitational waves, it’s proof of the initial expansion during the Big Bang and the continued inflation that has been taking place ever since.

bicep2-640x425Between 2010 and 2012, the BICEP2 – a radio telescope situated at the Amundsen–Scott South Pole Station (pictured above) – the research team listened to the Cosmic Microwave Background (CMB). They were looking for hints of B-mode polarization, a twist in the CMB that could only have been caused by the ripples of gravitational waves. Following a lot of data analysis, the leaders announced that they found that B-mode polarization.

The work will now be scrutinized by the rest of the scientific community, of course, but the general consensus seems confident that it will stand up. In terms of scientific significance, the confirmation of gravitational waves would be the first direct evidence that the universe started out as nothing, erupted into existence 13.8 billion years ago, and has continued to expand ever since. This would confirm that cosmic inflation really exists and that the entire structure of the universe was decided in the beginning by the tiniest flux of gravitational waves.

planck-attnotated-580x372And that’s not only discovery of cosmic significance that was made in recent months. In this case, the news comes from NASA’s Fermi Gamma-ray Space Telescope, which has been analyzing high-energy gamma rays emanating from the galaxy’s center since 2008. After pouring over the results, an independent group of scientists claimed that they had found an unexplained source of emissions that they say is “consistent with some forms of dark matter.”

These scientists found that by removing all known sources of gamma rays, they were left with gamma-ray emissions that so far they cannot explain. And while they were cautious that more observations will be needed to characterize these emissions, this is the first time that potential evidence has been found that may confirm that this mysterious, invisible mass that accounts for roughly 26.8% of the universe actually exists.

darkmatter1To be fair, scientists aren’t even sure what dark matter is made of. In fact, it’s very existence is inferred from gravitational effects on visible matter and gravitational lensing of background radiation. Originally, it was hypothesized to account for the discrepancies that were observed between the calculations of the mass of galaxies, clusters and entire universe made through dynamical and general relativistic means, and  the mass of the visible “luminous” matter.

The most widely accepted explanation for these phenomena is that dark matter exists and that it is most probably composed of Weakly Interacting Massive Particles (WIMPs) that interact only through gravity and the weak force. If this is true, then dark matter could produce gamma rays in ranges that Fermi could detect. Also, the location of the radiation at the galaxy’s center is an interesting spot, since scientists believe that’s where dark matter would lurk since the insofar invisible substance would be the base of normal structures like galaxies.

fermi_gamma-raysThe galactic center teems with gamma-ray sources, from interacting binary systems and isolated pulsars to supernova remnants and particles colliding with interstellar gas. It’s also where astronomers expect to find the galaxy’s highest density of dark matter, which only affects normal matter and radiation through its gravity. Large amounts of dark matter attract normal matter, forming a foundation upon which visible structures, like galaxies, are built.

Dan Hooper, an astrophysicist at Fermilab and lead author of the study, had this to say on the subject:

The new maps allow us to analyze the excess and test whether more conventional explanations, such as the presence of undiscovered pulsars or cosmic-ray collisions on gas clouds, can account for it. The signal we find cannot be explained by currently proposed alternatives and is in close agreement with the predictions of very simple dark matter models.

Hooper and his colleagues suggest that if WIMPs were destroying each other, this would be “a remarkable fit” for a dark matter signal. They again caution, though, that there could be other explanations for the phenomenon. Writing in a paper submitted to the journal Physical Review D, the researchers say that these features are difficult to reconcile with other explanations proposed so far, although they note that plausible alternatives not requiring dark matter may yet materialize.

CERN_LHCAnd while a great deal more work is required before Dark Matter can be safely said to exist, much of that work can be done right here on Earth using CERN’s own equipment. Tracy Slatyer, a theoretical physicist at the Massachusetts Institute of Technology and co-author of the report, explains:

Dark matter in this mass range can be probed by direct detection and by the Large Hadron Collider (LHC), so if this is dark matter, we’re already learning about its interactions from the lack of detection so far.This is a very exciting signal, and while the case is not yet closed, in the future we might well look back and say this was where we saw dark matter annihilation for the first time.

Still, they caution that it will take multiple sightings – in other astronomical objects, the LHC, or direct-detection experiments being conducted around the world – to validate their dark matter interpretation. Even so, this is the first time that scientists have had anything, even tentative, to base the existence of Dark Matter’s on. Much like until very recently with the Big Bang Theory, it has remained a process of elimination – getting rid of explanations that do not work rather than proving one that does.

So for those hoping that 2014 will be the year that the existence of Dark Matter is finally proven – similar to how 2012 was the year the Higgs Boson was discovered or 2013 was the year the Amplituhedron was found – there are plenty of reasons to hope. And in the meantime, check out this video of a gamma-ray map of the galactic center, courtesy of NASA’s Goddard Space Center.


Sources:
extremetech.com, IO9.com, nasa.gov, cfa.harvard.edu, news.nationalgeographic.com

Creating Dark Matter: The DarkLight Project

https://i2.wp.com/scienceblogs.com/startswithabang/files/2011/08/dark_matter_millenium_simulation.jpegFor several decades now, the widely accepted theory is that almost 27% of the universe is fashioned out of an invisible, mysterious mass known as “dark matter”. Originally theorized by Fritz Zwicky in 1933, the concept was meant to account for the “missing mass” apparent in galaxies in clusters. Since that time, many observations have suggested its existence, but definitive proof has remained elusive.

Despite our best efforts, no one has ever observed dark matter directly (nor dark energy, which is theorized to make up the remaining 68% of the universe). It’s acceptance as a theory has been mainly due to the fact that it makes the most sense, beating out theories like Modified Newtonian Dynamics (MOND), which seek to redefine the laws of gravity as to why the universe behaves the way it does.

https://i2.wp.com/www.extremetech.com/wp-content/uploads/2013/04/cdms.jpgLuckily, MIT recently green-lighted the DarkLight project – a program aimed at creating tiny tiny amounts of dark matter using a particle accelerator. In addition to proving that dark matter exists, the project team has a more ambitious goal of figuring out dark matter behaves – i.e. how it exerts gravitational attraction on the ordinary matter that makes up the visible universe.

The leading theory for dark matter used to be known as WIMPs (weakly interacting massive particles). This theory stated that dark matter only interacted with normal matter via gravity and the weak nuclear force, making them very hard to detect. However, a recent research initiative challenged this view and postulates that dark matter may actually consist of massive photons that couple to electrons and positrons.

https://i1.wp.com/www.extremetech.com/wp-content/uploads/2013/10/prototype-a-prime-dark-matter-detector.jpgTo do this, DarkLight will use the particle accelerator at the JeffersonJefferson Lab’s Labs Free-Electron Laser Free Electron Lase in Virginia to bombard an oxygen target with a stream of electrons with one megawatt of power. This will be able to test for these massive photons and, it is hoped, create this theorized form of dark matter particles. The dark matter, if it’s created, will then immediately decay into two other particles that can be (relatively) easily detected.

At this point, MIT estimates that it will take a couple of years to build and test the DarkLight experiment, followed by another two years of smashing electrons into the target and gathering data. By then, it should be clear whether dark matter consists of A prime particles, or whether scientists and astronomers have barking up the wrong tree these many years.

https://i2.wp.com/scienceblogs.com/startswithabang/files/2012/12/sim3dnew.pngBut if we can pinpoint the basis of dark matter, it would be a monumental finding that would greatly our enhance our understanding of the universe, and dwarf even the discovery of the Higgs Boson. After that, the only remaining challenge will be to find a way to observe and understand the other 68% of the universe!

Source: extremetech.com