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  • richardmitnick 2:43 pm on September 1, 2015 Permalink | Reply
    Tags: , , , Dark Energy/Dark Matter   

    From CAASTRO: “First year of Australia hunting for Black Holes and Dark Energy” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    1 September 2015

    Type Ia supernovae provided some of the first evidence for the accelerating Universe and remain among the most import tools for cosmology. The Dark Energy Survey (DES) Supernova Search is a new generation experiment that will discover more than 3000 Type Ia supernovae. This will be the largest coherent sample to date and used to make the best ever measurement of the Universe’s expansion history. Traditionally, spectroscopy of a live supernova within a few weeks of maximum light serves the dual purpose of “typing” the transient (i.e. determining whether it is a Type Ia supernova) and measuring its redshift, both of which parameters are critical for putting the supernova onto a Hubble diagram. However, this method requires an unrealistically large amount of resources for a large number of supernovae such as DES will collect. Alternatively, redshifts can be measured by observing supernova host galaxies at any time after the supernova discoveries. With the help of these redshifts, light curves can be used to reliably identify Type Ia supernovae.

    The Australian Dark Energy Survey (OzDES) is a five-year, 100-night program that will use the 400 fibre 2dF system and AAOmega spectrograph on the Anglo-Australian Telescope [AAT] to measure redshifts of 2,500 Type Ia supernovae host galaxies from DES.

    Anglo Australian Telescope Exterior
    Anglo Australian Telescope Interior

    Bringing together the power of multi-fibre spectrograph and time series observations (roughly monthly during the DES season), OzDES will also monitor more than 500 active galactic nuclei and quasars to measure their black hole masses, classify live DES transients and provide calibration data for other DES programs probing the Universe’s structure and evolution.


    In this paper, we present an overview of the OzDES program and results from its first year of operation. In the first year, OzDES observed over 10,000 objects and measured more than 6,000 redshifts. We are achieving goals in terms of efficiency, redshift reliability and precision, while we continue to improve data quality. The large number of spectra taken by OzDES also guarantees discoveries of rare events or objects. We highlight a few cases that stand out, including some galaxy-galaxy lens candidates.

    Publication details:
    Fang Yuan, C. Lidman, T. M. Davis, M. Childress et al. in MNRAS (2015) “OzDES multi-fibre spectroscopy for the Dark Energy Survey: first-year operation and results

    See the full article here.

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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.


    The University of Sydney
    The University of Western Australia
    The University of Melbourne
    Swinburne University of Technology
    The Australian National University
    Curtin University
    University of Queensland

  • richardmitnick 11:58 am on August 23, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, U Southern Denmark   

    From USD: “New theory: If we want to detect dark matter we might need a different approach” 

    USD bloc

    University of Southern Denmark


    Associate professor Mads Toudal Frandsen, tel +6550 4521. Email: frandsen@cp3.dias.sdu.dk.
    Postdoc Ian Shoemaker. Email shoemaker@psu.edu.

    Physicists suggest a new way to look for dark matter: They believe that dark matter particles annihilate into so-called dark radiation when they collide. If true, then we should be able to detect the signals from this radiation.

    ­The majority of the mass in the Universe remains unknown. Despite knowing very little about this dark matter, its overall abundance is precisely measured. In other words: Physicists know it is out there, but they have not yet detected it.

    It is definitely worth looking for, argues Ian Shoemaker, former postdoctoral researcher at Centre for Cosmology and Particle Physics Phenomenology (CP3), Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, now at Penn State, USA.

    The Large Underground Xenon (LUX) experiment is placed in this former mine almost 1500 m underground in South Dakota, USA. Credit: Matt Kapust, Sanford Underground Research Facility.

    “There is no way of predicting what we can do with dark matter, if we detect it. But it might revolutionize our world. When scientists discovered quantum mechanics, it was considered a curiosity. Today quantum mechanics plays an important role in computers”, he says.

    Ever since dark matter was first theorized there have been many attempts to look for it, and now Ian Shoemaker and fellow scientists, Associate Professor Mads Toudal Frandsen, CP3, and John F. Cherry, postdoctoral researcher from Los Alamos National Laboratory, USA, suggest a new approach. They present their work in the journal Physical Review Letters.

    Look in underground caves

    On Earth several detectors are placed in underground cavities, where disturbing noise is minimized. The hope is that one of these detectors will one day catch a dark matter particle passing through Earth.

    According to Ian Shoemaker, it is possible that this might happen, but given how little we know about dark matter we should keep an open mind and explore all paths that could lead to its detection.

    One reason for this is that dark matter is not very dense in our part of the universe.

    This is the LUX detector. Credit: Matt Kapust, Sanford Underground Research Facility.

    “If we add another way of looking for dark matter – the way, we suggest – then we will increase our chances of detecting dark matter in our underground cavities”, says Shoemaker.

    He and his colleagues now suggest looking for the signs of dark matter activity rather than the dark matter particles themselves.

    The researchers believe that when two dark matter particles meet, they will behave just like ordinary particles; that they will annihilate and create radiation in the process. In this case the radiation is called dark radiation, and it may be detected by the existing underground detectors.

    “Underground detection experiments may be able to detect the signals created by dark radiation”, Shoemaker says.

    The researchers have found that the Large Underground Xenon (LUX) experiment is in fact already sensitive to this signal and can with future data confirm or exclude their hypothesis for dark matter’s origin.

    Don’t forget to look in the Milky Way, too

    The attempt to catch signals from dark radiation is not a new idea – it is currently being performed several places in space with satellite-based experiments. These places include the center of our galaxy, the Milky Way, and the Sun may also be such an area.

    “It makes sense to look for dark radiation in certain places in space, where we expect it to be very dense – a lot denser than on Earth”, explains Shoemaker, adding:

    “If there is an abundance of dark matter in these areas, then we would expect it to annihilate and create radiation.”

    None of the satellite-based experiments however have yet detected dark radiation.

    According to Shoemaker, Frandsen and Cherry, this could be because the experiments look for the wrong signals.

    “The traditional satellite-based experiments search for photons, because they expect dark matter to annihilate into photons. But if dark matter annihilates into dark radiation then these satellite-based experiments are hopeless.”

    In the early days of the universe, when all matter was still extremely dense, dark matter may have collided and annihilated into radiation all the time. This happened to ordinary matter as well, so it is not unlikely that dark matter behaves the same way, the researchers argue.

    Ref Direct Detection Phenomenology in Models Where the Products of Dark Matter Annihilation Interact with Nuclei, John F. Cherry, Mads T. Frandsen, and Ian M. Shoemaker. Phys. Rev. Lett. 114, 231303

    See the full article here.

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  • richardmitnick 5:02 pm on August 20, 2015 Permalink | Reply
    Tags: , , Dark Energy/Dark Matter, ,   

    From Berkeley: “Experiment attempts to snare a dark energy ‘chameleon’” 

    UC Berkeley

    UC Berkeley

    August 20, 2015
    Robert Sanders

    The vacuum chamber of the atom interferometer contains a one-inch diameter aluminum sphere. If chameleons exist, cesium atoms would fall toward the sphere with a slightly greater acceleration than their gravitational attraction would predict. (Holger Muller photo)

    If dark energy is hiding in our midst in the form of hypothetical particles called “chameleons,” Holger Müller and his team at UC Berkeley plan to flush them out.

    The results of an experiment reported in this week’s issue of Science narrows the search for chameleons a thousand times compared to previous tests, and Müller, an assistant professor of physics, hopes that his next experiment will either expose chameleons or similar ultralight particles as the real dark energy, or prove they were a will-o’-the-wisp after all.

    Dark energy was first discovered in 1998 when scientists observed that the universe was expanding at an ever increasing rate, apparently pushed apart by an unseen pressure permeating all of space and making up about 68 percent of the energy in the cosmos. Several UC Berkeley scientists were members of the two teams that made that Nobel Prize-winning discovery, and physicist Saul Perlmutter shared the prize.

    Since then, theorists have proposed numerous theories to explain the still mysterious energy. It could be simply woven into the fabric of the universe, a cosmological constant [Λ] that Albert Einstein proposed in the equations of general relativity and then disavowed. Or it could be quintessence, represented by any number of hypothetical particles, including offspring of the Higgs boson.

    In 2004, theorist and co-author Justin Khoury of the University of Pennsylvania proposed one possible reason why dark energy particles haven’t been detected: they’re hiding from us.

    If chameleons exist, they would have a very small effect on the gravitational attraction between cesium atoms and an aluminum sphere.

    Specifically, Khoury proposed that dark energy particles, which he dubbed chameleons, vary in mass depending on the density of surrounding matter.

    In the emptiness of space, chameleons would have a small mass and exert force over long distances, able to push space apart. In a laboratory, however, with matter all around, they would have a large mass and extremely small reach. In physics, a low mass implies a long-range force, while a high mass implies a short-range force.

    This would be one way to explain why the energy that dominates the universe is hard to detect in a lab.

    “The chameleon field is light in empty space but as soon as it enters an object it becomes very heavy and so couples only to the outermost layer of a big object, and not to the internal parts,” said Müller, who is also a faculty scientist at Lawrence Berkeley National Laboratory. “It would pull only on the outermost nanometer.”

    Lifting the camouflage

    When UC Berkeley post-doctoral fellow Paul Hamilton read an article by theorist Clare Burrage last August outlining a way to detect such a particle, he suspected that the atom interferometer he and Müller had built at UC Berkeley would be able to detect chameleons if they existed. Müller and his team have built some of the most sensitive detectors of forces anywhere, using them to search for slight gravitational anomalies that would indicate a problem with Einstein’s General Theory of Relativity. While the most sensitive of these are physically too large to sense the short-range chameleon force, the team immediately realized that one of their less sensitive atom interferometers would be ideal.

    The dark energy group: Holger Müller, Philipp Haslinger, Justin Khoury (on computer monitor), Matt Jaffe, Paul Hamilton. (Enar de Dios Rodriguez photo)

    Burrage suggested measuring the attraction caused by the chameleon field between an atom and a larger mass, instead of the attraction between two large masses, which would suppress the chameleon field to the point of being undetectable.

    That’s what Hamilton, Müller and his team did. They dropped cesium atoms above an inch-diameter aluminum sphere and used sensitive lasers to measure the forces on the atoms as they were in free fall for about 10 to 20 milliseconds. They detected no force other than Earth’s gravity, which rules out chameleon-induced forces a million times weaker than gravity. This eliminates a large range of possible energies for the particle.

    What about symmetrons?

    Experiments at CERN in Geneva and the Fermi National Accelerator Laboratory in Illinois, as well as other tests using neutron interferometers, also are searching for evidence of chameleons, so far without luck. Müller and his team are currently improving their experiment to rule out all other possible particle energies or, in the best-case scenario, discover evidence that chameleons really do exist.

    “Holger has ruled out chameleons that interact with normal matter more strongly than gravity, but he is now pushing his experiment into areas where chameleons interact on the same scale as gravity, where they are more likely to exist,” Khoury said.

    Their experiments may also help narrow the search for other hypothetical screened dark energy fields, such as symmetrons and forms of modified gravity, such as so-called f(R) gravity.

    “In the worst case, we will learn more of what dark energy is not. Hopefully, that gives us a better idea of what it might be,” Müller said. “One day, someone will be lucky and find it.”

    The work was funded by the David and Lucile Packard Foundation, the National Science Foundation and the National Aeronautics and Space Administration. Co-authors with Müller, Hamilton and Khoury are UC Berkeley physics graduate students Matt Jaffe and Quinn Simmons and post-doctoral fellow Philipp Haslinger.


    Atom-interferometry constraints on dark energy (preprint)
    Muller’s matter wave research group

    See the full article here..

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    Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

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  • richardmitnick 3:53 pm on August 20, 2015 Permalink | Reply
    Tags: , , Dark Energy/Dark Matter, James Bullock, ,   

    From Quanta: “The Case for Complex Dark Matter” 

    Quanta Magazine
    Quanta Magazine

    August 20, 2015
    Liz Kruesi

    The physicist James Bullock explains how a complicated “dark sector” of interacting particles may illuminate some puzzling observations of the centers of galaxies.

    James Bullock, a physicist at the University of California, Irvine, imagines what the universe would look like if dark matter interacted with itself.

    Dark matter — the unseen 80 percent of the universe’s mass — doesn’t emit, absorb or reflect light. Astronomers know it exists only because it interacts with our slice of the ordinary universe through gravity. Hence the hunt for this missing mass has focused on so-called WIMPs — Weakly Interacting Massive Particles — which interact with each other as infrequently as they interact with normal matter.

    Physicists have reasons to look for alternatives to WIMPs. For two decades, astronomers have found less dark matter at the centers of galaxies than what WIMP models suggest they should. The discrepancy is even worse at the cores of the universe’s tiny dwarf galaxies, which have few ordinary stars but lots of dark matter.

    About four years ago, James Bullock, a professor of physics and astronomy at the University of California, Irvine, began to wonder whether the standard view of dark matter was failing important empirical tests. “This was the point where I really started thinking hard about alternatives,” he said.

    Bullock thinks that dark matter might instead be complex, something that interacts with itself strongly in the way that ordinary matter interacts with itself to form intricate structures like atoms and atomic elements. Such a self-interacting dark matter, Bullock suspects, could exist in a “dark sector,” somewhat parallel to our own light sector, but detectable only through the way it affects gravity.

    He and his colleagues have created numerical simulations that predict what the universe would look like if dark matter feels strong interactions. They expected to see the model fail. Instead, they found that it was consistent with what astronomers observe.

    Quanta Magazine spoke with Bullock about complex dark matter, how this mysterious mass might behave, and the best places in the universe to find it. An edited and condensed version of the interview follows.

    QUANTA MAGAZINE: What do we know about dark matter?

    JAMES BULLOCK: We are confident that it’s there, that it has mass, and that it tugs on itself and on other things via gravity. That’s about it. While dark matter has a gravitational tug, it doesn’t interact with normal matter — the stuff that makes up you and me — in a very intense way. It doesn’t shine. It’s invisible. It’s transparent. It doesn’t glow when it gets hot. Unfortunately, those are the ways astronomers usually study the universe; we usually follow the light.

    So we don’t know what it’s made of?

    We’ve come to understand that we can describe the world that we experience by the Standard Model of particle physics.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    We think of the particles that make up you and me as being broken down into constituent things, like quarks, and those quarks combine into neutrons and protons. There is a complicated dance that allows these particles to interact in certain ways. It gives rise to the periodic table of elements and all of the vast complexity we see around us. Just 20 percent of the mass of the universe is all of this complexity.

    On the other hand, dark matter makes up something like 80 percent of the mass. First-guess models for what it is suggests that it is one particle that doesn’t really interact with much of anything — WIMPs. These are collisionless, meaning when two dark matter particles come at each other they basically go through each other.

    Another possibility is this 80 percent of the universe is also complex. Maybe there’s something interesting going on in what’s called the dark sector. We know that whatever ties us to the dark matter is pretty weak or else we would have already seen it. This observation has led to the belief that all the interactions that could be going on with dark matter are weak. But there’s another possibility: When dark matter particles see themselves, there are complex and potentially very strong interactions. There even could be dark atoms and dark photons.

    Those two worlds — this dark sector and our own sector — only communicate by gravity and perhaps other weak processes, which haven’t yet been seen.

    How can you probe this dark sector if you can’t interact with it?

    Now what we’re talking about doing is not just looking at the gross properties of the dark matter but the very makeup of the dark matter, too. The most obvious place to see those effects is where dark matter is bunched up. We believe the centers of galaxies and galaxy clusters are densest. And so by studying the behavior of dark matter by indirect methods — basically by the dynamics of stars and gas and galaxies in galaxy clusters — we can start to understand how dark matter is distributed in space. To start to discriminate between models, we can compare differences in dark matter’s spatial clumpiness in simulations, for example, and then look for those differences in data.

    What does the data say?

    In models using cold, collisionless dark matter — WIMPs — the dark matter is very dense at the middle of galaxies. It appears that those predicted densities are much higher than what’s observed.

    What might be going on is that something a little more complex is happening in the dark sector, and that complexity is causing these slight disagreements between theory and observation at places where the dark matter is really clumped or starts congregating, like in the centers of galaxies or the centers of galaxy clusters.

    I’m interested in running cosmological simulations of how the universe should evolve from the very beginning until now. I look at what happens, when I run those simulations forward, if I allow cold dark matter to occasionally collide and exchange energy. The simulations start with a small, almost-smooth primordial universe and end with beautiful agreement with large-scale structure — galaxies stretched out across the universe in the way we observe them. But the hearts of galaxies are less dense in dark matter in my simulations than they are in simulations where the dark matter is cold and collisionless.

    How long have researchers known about these disagreements between the models and the data?

    We’ve known that there’s a bit of a problem at the centers of galaxies for about 20 years. At first it was thought maybe we’re interpreting the data wrong. And now the question comes down to: Does galaxy formation eject dark matter somehow, or do we need to modify our understanding of dark matter?

    Why did you start looking into self-interacting dark matter?

    The first paper exploring ideas that the dark matter might be more complex was in Physical Review Letters, April 2000, by David Spergel and Paul Steinhardt. I actually started working on this several years later when I began seeing papers from the particle physics community exploring these ideas. My initial reaction was, that couldn’t be true, because I had this prejudice that things work so well with collisionless dark matter.

    In the first set of simulations we ran, we gave dark matter a cross-section with itself. The bigger the cross-section is, the higher the probability that these particles are going to run into one another in any given amount of time. We set the value of the cross-section to something we were convinced would be ruled out [by the data], but when we ran our simulation we found that we couldn’t see any difference between that model and the classic one. And so we thought maybe we don’t know quite as much as we thought we knew.

    Then, we dialed it up and looked at a strong interaction similar to if you threw two neutrons together. We saw something that looks really close to observations on large scales but does produce differences in the hearts of galaxies. Rather than the dark matter getting denser and denser as you approach the center of the galaxy, it reached a threshold density.

    Could it be that these little discrepancies we’ve been seeing in the observational data are actually a clue that there’s something interesting and fun going on in the dark sector that we weren’t thinking about before?

    How have these simulations evolved since the first ones you performed?

    We’ve been running very high cross-section values to see when this model starts to break compared to some observations. We’re also focusing energy on including all of the star-formation and galaxy-formation physics in these simulations. The hardest part with these simulations is that the universe isn’t just made of dark matter. There’s all of this other annoying normal stuff that we have to think about, too. Gas that can turn into stars — and some of those stars are going to be so massive that they blow up as supernovae. When they blow up as supernovae, they are effectively jostling the gravitational field around them, and this jostling can potentially move the dark matter around. Is it possible that these discrepancies that we’re seeing in the observed densities of dark matter and the predicted densities of dark matter is because the galaxy-formation process itself is changing things in a way that we don’t understand very well?

    Something else that I spend my time on is figuring out the cleanest and clearest cases for determining what comes from the physics of dark matter versus the physics of star formation and galaxy formation. We have to think hard about how clean our cosmological experiments are.

    Where is that cleanest cosmological laboratory?

    My opinion is that the cleanest sites are the teeniest, tiniest galaxies we know about — dwarf galaxies. They have very few stars but huge amounts of dark matter. In some cases they have 100 times as much dark matter within their visible extent as they have visible matter. (The Milky Way interior to the Sun is about half dark matter and half normal matter.) Dwarf galaxies have so much dark matter compared to their stars, they’re excellent laboratories for dark matter. They’re as clean as we have.

    But studying dark matter physics in something that doesn’t give off much light is pretty difficult.

    The nice thing about these objects is that a lot of them are really close by. They’re close enough that you can actually measure the velocities of individual stars. That allows you to build as precise a model as you can of the dark matter density at the centers of these galaxies. They’re close enough to study with great precision, but they’re chock full of dark matter so you don’t have to worry as much about what’s going on with the stars.

    There have been recent observational studies focusing on galaxy clusters. Are observations and theoretical models starting to move in a similar direction?

    Imagine a swarm of bees; a cluster of galaxies is sort of like that. Massive collisions, where two galaxy clusters have come at each other and pass through each other, are one place to look for complex dark matter. If the dark matter is strongly interacting, when those massive clusters come together, the galaxies will keep flying right on through, but the dark matter, because it’s strongly interacting with itself, will sort of bunch up in the middle.

    The Bullet Cluster shows the aftermath of a cosmic collision between two galaxy clusters. In this false-color image, the hot gas (pink) slowed down in the collision due to a drag force, while the dark matter (blue) appeared to keep passing through, as one would expect if dark matter is collisionless.

    In the famous example of the Bullet Cluster, astronomers used the effect of gravitational lensing to look at where the dark matter was. They found that the dark matter has moved right on through along with the galaxies, which is what you’d expect with collisionless dark matter. Because of this result, people said, “Well, there’s no way the dark matter is strongly interacting with itself.”

    That was a few years ago and a couple things have happened since then. We’ve realized that a lot of the first-order estimates people have used to determine how much the dark matter ought to drag on itself were overestimated. Also, several other clusters have less-clear results, and in some cases maybe there is more drag than we thought before. Richard Massey’s group found evidence that some kind of dark pressure, ram pressure, is ripping the dark matter out of a galaxy.

    We really aren’t at the point yet where I think we’ve done enough, though. We need to invest more effort into simulating the calculations properly with these various classes of dark matter to figure out what it is we know and what it is we don’t know. I think we’ve seen exciting hints, and they motivate us to try to do as well as we can to figure out what they mean.

    See the full article here.

    [James Bullock was featured in the NatGeo TV special Inside the Milky Way, which I have presented many times. But, hey, it might be the single greatest science video ever made, so, what is wrong with one more time? If you have not seen it, you are in for a treat. As I say often when presenting a video, watch, enjoy, learn.]

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

  • richardmitnick 11:45 am on August 17, 2015 Permalink | Reply
    Tags: , , , Dark Energy/Dark Matter,   

    From FNAL: “Dark Energy Survey finds more celestial neighbors” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    New dwarf galaxy candidates could mean our sky is more crowded than we thought.

    Temp 1

    Media contact:

    Andre Salles, Fermilab Office of Communication, media@fnal.gov, 630-840-3351

    Science contacts:

    Josh Frieman, Fermilab, director of the Dark Energy Survey, frieman@fnal.gov, 847-274-0429
    Alex Drlica-Wagner, David N. Schramm fellow, Fermilab, kadrlica@fnal.gov
    Keith Bechtol, John Bahcall fellow, University of Wisconsin-Madison, keith.bechtol@icecube.wisc.edu
    Risa Wechsler, SLAC/Stanford University, risa@slac.stanford.edu
    Basilio Santiago, Federal University of Rio Grande do Sul, basilio.santiago@ufrgs.br

    Scientists on the Dark Energy Survey, using one of the world’s most powerful digital cameras, have discovered eight more faint celestial objects hovering near our Milky Way galaxy. Signs indicate that they, like the objects found by the same team earlier this year, are likely dwarf satellite galaxies, the smallest and closest known form of galaxies.

    Dark Energy Survey
    Dark Energy Camera
    Dark Energy Camera

    Satellite galaxies are small celestial objects that orbit larger galaxies, such as our own Milky Way. Dwarf galaxies can be found with fewer than 1,000 stars, in contrast to the Milky Way, an average-size galaxy containing billions of stars. Scientists have predicted that larger galaxies are built from smaller galaxies, which are thought to be especially rich in dark matter, the substance that makes up about 25 percent of the total matter and energy in the universe. Dwarf satellite galaxies, therefore, are considered key to understanding dark matter and the process by which larger galaxies form.

    The main goal of the Dark Energy Survey (DES), as its name suggests, is to better understand the nature of dark energy, the mysterious stuff that makes up about 70 percent of the matter and energy in the universe. Scientists believe that dark energy is the key to understanding why the expansion of the universe is speeding up. To carry out its dark energy mission, DES takes snapshots of hundreds of millions of distant galaxies. However, some of the DES images also contain stars in dwarf galaxies much closer to the Milky Way. The same data can therefore be used to probe both dark energy, which scientists think is driving galaxies apart, and dark matter, which is thought to hold galaxies together.

    Scientists can only see the faintest dwarf galaxies when they are nearby, and had previously only found a few of them. If these new discoveries are representative of the entire sky, there could be many more galaxies hiding in our cosmic neighborhood.

    “Just this year, more than 20 of these dwarf satellite galaxy candidates have been spotted, with 17 of those found in Dark Energy Survey data,” said Alex Drlica-Wagner of the U.S. Department of Energy’s (DOE) Fermi National Accelerator Laboratory, one of the leaders of the DES analysis. “We’ve nearly doubled the number of these objects we know about in just one year, which is remarkable.”

    In March, researchers with the Dark Energy Survey and an independent team from the University of Cambridge jointly announced the discovery of nine of these objects in snapshots taken by the Dark Energy Camera, the extraordinary instrument at the heart of the DES, an experiment funded by the DOE, the National Science Foundation and other funding agencies. Two of those have been confirmed as dwarf satellite galaxies so far.

    Prior to 2015, scientists had located only about two dozen such galaxies around the Milky Way.

    “DES is finding galaxies so faint that they would have been very difficult to recognize in previous surveys,” said Keith Bechtol of the University of Wisconsin-Madison. “The discovery of so many new galaxy candidates in one-eighth of the sky could mean there are more to find around the Milky Way.”

    The closest of these newly discovered objects is about 80,000 light-years away, and the furthest roughly 700,000 light-years away. These objects are, on average, around a billion times dimmer than the Milky Way and a million times less massive. The faintest of the new dwarf galaxy candidates has about 500 stars.

    Most of the newly discovered objects are in the southern half of the DES survey area, in close proximity to the Large Magellanic Cloud and the Small Magellanic Cloud. These are the two largest satellite galaxies associated with the Milky Way, about 158,000 light-years and 208,000 light-years away, respectively. It is possible that many of these new objects could be satellite galaxies of these larger satellite galaxies, which would be a discovery by itself.

    “That result would be fascinating,” said Risa Wechsler of DOE’s SLAC National Accelerator Laboratory. “Satellites of satellites are predicted by our models of dark matter. Either we are seeing these types of systems for the first time, or there is something we don’t understand about how these satellite galaxies are distributed in the sky.”

    Since dwarf galaxies are thought to be made mostly of dark matter, with very few stars, they are excellent targets to explore the properties of dark matter. Further analysis will confirm whether these new objects are indeed dwarf satellite galaxies and whether signs of dark matter can be detected from them.

    The 17 dwarf satellite galaxy candidates were discovered in the first two years of data collected by the Dark Energy Survey, a five-year effort to photograph a portion of the southern sky in unprecedented detail. Scientists have now had a first look at most of the survey area, but data from the next three years of the survey will likely allow them to find objects that are even fainter, more diffuse or farther away. The third survey season has just begun.

    “This exciting discovery is the product of a strong collaborative effort from the entire DES team,” said Basilio Santiago, a DES Milky Way Science Working Group coordinator and a member of the DES-Brazil Consortium. “We’ve only just begun our probe of the cosmos, and we’re looking forward to more exciting discoveries in the coming years.”

    View the Dark Energy Survey analysis online. Follow the Dark Energy Survey on Facebook and Twitter. For images taken with the Dark Energy Camera, visit the experiment’s photo blog, Dark Energy Detectives.

    The Dark Energy Survey is a collaboration of more than 300 scientists from 25 institutions in six countries. Its primary instrument, the 570-megapixel Dark Energy Camera, is mounted on the 4-meter Blanco telescope at the National Optical Astronomy Observatory’s Cerro Tololo Inter-American Observatory in Chile, and its data is processed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    Victor M. Banco 4m telescope

    Funding for the DES Projects has been provided by the U.S. Department of Energy Office of Science, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, ETH Zurich for Switzerland, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência e Tecnologia, the Deutsche Forschungsgemeinschaft and the collaborating institutions in the Dark Energy Survey, which can be found at http://www.darkenergysurvey.org/collaboration.

    The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

    See the full article here.

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

  • richardmitnick 11:43 am on August 15, 2015 Permalink | Reply
    Tags: , , Dark Energy/Dark Matter,   

    From Techniche Universitat Munchen: “Dark matter at the heart of our Galaxy” 

    Techniche Universitat Munchen

    Techniche Universitat Munchen

    Dr. Andreas Battenberg

    View towards the center of our Galaxy with the rotation curve tracers – Background photo: Serge Brunier / NASA

    The Universe is pervaded by a mysterious form of matter, dubbed dark matter, about five times more abundant than the ordinary matter – made of atoms – we are familiar with. Its existence in galaxies was robustly established in the 1970s. Scientists now obtained for the first time a direct observational proof of the presence of dark matter in the innermost part our Galaxy, the Milky Way.

    The ubiquitous presence of dark matter in the universe is today a central tenet in modern cosmology and astrophysics. Its existence in galaxies was robustly established in the 1970s with a variety of techniques, including the measurement of the rotation speed of gas and stars, which provides a way to effectively ‘weigh’ the host galaxy and determine its total mass. These measurements showed that the visible matter only accounts for a fraction of the total weight, the predominant part is delivered by dark matter.

    Applying this technique to our own Galaxy is possible, and the existence of dark matter in the outer parts of the Milky Way is well ascertained. But up to now it has proven very difficult to establish the presence of dark matter in the innermost regions.

    The diameter of our Galaxy is about 100,000 lightyears. Our Solar System is located at a distance of about 26,000 light years from the center. Coming closer to the center of our galaxy it becomes increasingly difficult to measure the rotation of gas and stars with the needed precision.

    Dark matter in our cosmic neighborhood

    Now scientists from the Technische Universität München (TUM), Stockholm University, Universidad Autónoma de Madrid, ICTP South American Institute for Fundamental Research, São Paulo and University of Amsterdam have obtained for the first time a direct observational proof of the presence of dark matter in the innermost part the Milky Way, including at the Earth’s location and in our own ‘cosmic neighborhood’.

    In a first step they created the most complete compilation of published measurements of the motion of gas and stars in the Milky Way. Then they compared the measured rotation speed with that expected under the assumption that only luminous matter exists in the Galaxy. The comparison clearly showed that the observed rotation cannot be explained unless large amounts of dark matter exist around us, and between us and the galactic center.

    “We know that dark matter is needed in our Galaxy to keep the stars and gas rotating at their observed speeds,” says Dr. Miguel Pato, who conducted the analysis at TU München. “However, we still do not know what dark matter is composed of. This is one of the most important science questions of our times.”

    More reliable predictions

    Possessing a very strong statistical evidence, even at small galactocentric distances, the results open a new avenue for the determination of dark matter distribution inside the Galaxy. With future astronomical observations, the method will allow to measure the distribution of dark matter in our Galaxy with unprecedented precision.

    “This will permit to refine the understanding of the structure and evolution of our Galaxy. And it will trigger more robust predictions for the many experiments worldwide that search for dark matter particles,” says Miguel Pato, who meanwhile moved to The Oskar Klein Centre for Cosmoparticle Physics at the Stockholm University.


    Evidence for dark matter in the inner Milky Way
    Fabio Iocco, Miguel Pato, Gianfranco Bertone
    Nature Physics, advanced online publication, 9 February 2015
    DOI: 10.1038/nphys3237

    [No observational tools, telescopes, spacecraft, etc., weakens this article]

    See the full article here.

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    Techniche Universitat Munchin Campus

    Technische Universität München (TUM) is one of Europe’s top universities. It is committed to excellence in research and teaching, interdisciplinary education and the active promotion of promising young scientists. The university also forges strong links with companies and scientific institutions across the world. TUM was one of the first universities in Germany to be named a University of Excellence. Moreover, TUM regularly ranks among the best European universities in international rankings.

  • richardmitnick 3:04 pm on August 5, 2015 Permalink | Reply
    Tags: , , Dark Energy/Dark Matter,   

    From NASA Blueshift: “Black Hole Laboratories for Dark Matter” 

    NASA Blueshift
    NASA Blueshift

    August 5, 2015
    Maggie Masetti

    There is a lot we don’t know about dark matter – like what exactly it is. Because of this, we are always looking for ways to study it. It turns out that black holes might make the perfect laboratory environment for better understanding both black holes and the nature of dark matter.

    We talked to Dr. Jeremy Schnittman, the Goddard astrophysicist who has been working on computer simulations exploring the connections between black holes and dark matter. We had the opportunity to chat with him and had him give us the basics of his ideas.

    NASA Blueshift: What is dark matter? Why do we call it “dark”?

    Dr. Jeremy Schnittman: Dark matter is a hypothetical particle that pervades the entire universe, contributing more than five times more mass than normal matter like protons and electrons. While we have not yet actually seen dark matter directly (and thus, we call it “dark”), we see ample evidence for its existence through indirect means such as gravity.

    NASA Blueshift: What makes us think dark matter exists, if we can’t directly detect it?

    Dr. Jeremy Schnittman: The force of gravity is directly proportional to the total amount of mass present. So if you can measure how a star or galaxy is moving due to gravitational forces, it is straight-forward to measure how much mass is pulling on it. By looking at radiation like starlight and radio waves, we can measure how much of this mass is due to stars and gas, and in most cases, the answer is “not nearly enough mass!” The rest is attributed to dark matter.

    NASA Blueshift: Why would black holes be a good place to look for/at dark matter?

    Dr. Jeremy Schnittman: To better understand normal particles like protons and electrons, we typically accelerate them in a particle collider, smash them together, and look at the pieces that fly out. Since dark matter only interacts with gravity, we need a gravitational particle accelerator. Nothing does gravity better than a black hole! So not only does it attract a higher density of particles, but also increases the energy of their collisions.

    NASA Blueshift: Why do researchers use computer simulations? How do they differ from direct observations?

    Dr. Jeremy Schnittman: Before building a large, expensive space telescope, it is crucial to have a reliable prediction for what it will see. Computer simulations are much cheaper, and with increasing computer power, they are increasingly reliable. Yet experience teaches us to always expect the unexpected, and computer simulations almost by definition can ONLY predict things that are already expected. So it is always worth the time and money to go out and do real observations.

    This visualization shows dark matter particles as gray spheres attached to shaded trails representing their motion. Redder trails indicate particles more strongly affected by the black hole’s gravitation and closer to its event horizon (black sphere at center, mostly hidden by trails). The ergosphere, where all matter and light must follow the black hole’s spin, is shown in teal. The black hole is viewed along its equator and rotates left to right. Credits: NASA Goddard’s Scientific Visualization Studio and NASA Goddard/Jeremy Schnittman

    This image shows the gamma-ray signal produced in the computer simulation by annihilations of dark matter particles. Lighter colors indicate higher energies, with the highest-energy gamma rays originating from the center of the crescent-shaped region at left, closest to the black hole’s equator and event horizon. The gamma rays with the greatest chances of escape are produced on the side of the black hole that spins toward us. Such lopsided emission is typical for a rotating black hole. Credits: NASA Goddard/Jeremy Schnittman

    NASA Blueshift: What’s next for this research after this simulation?

    Dr. Jeremy Schnittman: Fortunately, we already have a space telescope in place for these observations: the Fermi Gamma-ray Observatory.

    NASA Fermi Telescope

    We plan to use existing data from Fermi to search for evidence of dark matter around known black holes. At the very least, we expect to be able to place new, more stringent limits on the properties of dark matter, such as the particle mass and cross section.

    NASA Blueshift: Thanks, Jeremy!

    You can read more about his computer simulations in this NASA feature article, and you can also watch the below video:

    See the full article here.

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    Blueshift is produced by a team of contributors in the Astrophysics Science Division at Goddard. Started in 2007, Blueshift came from our desire to make the fascinating stuff going on here every day accessible to the outside world.

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  • richardmitnick 4:29 pm on July 29, 2015 Permalink | Reply
    Tags: , , Dark Energy/Dark Matter,   

    From Physics- “Viewpoint: Sky Survey Casts Light on the Dark Universe” 

    Physics LogoAbout Physics

    Physics Logo 2


    July 29, 2015
    Catherine Heymans, Institute for Astronomy, University of Edinburgh

    The Dark Energy Survey has generated a map of invisible dark matter by observing tiny gravitationally induced distortions in the images of distant galaxies

    As the light from distant galaxies travels to us, it passes by massive structures filled with invisible dark matter (shown here as gray spheres). The gravity from this dark matter warps the surrounding spacetime, causing distortions in the perceived shapes of the background galaxies. Each galaxy becomes slightly elongated (more elliptical), depending on the distribution of dark matter along its light path. Galaxies near to each other in the sky (as shown on the left side) are distorted equally, making them appear more aligned. By measuring this alignment, astronomers can infer the size and location of massive structures (dotted circles), and thereby construct a map of the dark matter. APS/Alan Stonebraker; galaxy images from STScI/AURA, NASA, ESA, and the Hubble Heritage Team

    If you talked to any cosmologist today, you would most likely witness two conflicting emotions. The first is quite self-congratulatory as the community has collectively nailed down the precise quantities of each component in the Universe, using multiple independent observations. The second is one of panic, when they admit that the major dark constituents of the Universe that are inferred to exist remain elusive. The Dark Energy Survey (DES) is one of three optical imaging surveys in this decade’s hot competition to uncover the true nature of the dark side of our Universe. One way to demonstrate the future potential of these surveys is to identify and map dense clumps of dark matter through the distortions they cause in the perceived shapes of background galaxies. Chihway Chang of the Swiss Federal Institute of Technology (ETH) in Zurich, and Vinu Vikram of Argonne National Laboratory, Illinois, present a map of dark matter from the first 3% of data from DES, which is observing the Southern Sky over a full five-year mission [1, 2]. This very first glimpse reveals just how powerful this new sky survey will become in its quest to understand dark energy, which is driving the acceleration of the Universe and thereby affecting the distribution of the dark matter that they have mapped.

    Dark matter is invisible, but it makes up 84% of all the matter in the Universe [3]. We only infer its presence because of the effect it has on both the light and matter that we can see. In the early Universe, the dominant clumps of dark matter gravitationally attract the normal matter that will go on to form the galaxies that we can see today. Dark matter really dictates where and when galaxies form in the Universe.

    Dark energy constitutes 68.5% of the total cosmic energy density of the Universe, apparently providing extra fuel to accelerate the post big-bang expansion of the Universe. Recent rapid expansion would make it hard for large-scale structures of matter to form and grow. Scientists hope to uncover the origin of dark energy by observing how it affects the growth of structures in the Universe over time.

    Einstein’s theory of general relativity tells us that mass curves spacetime. As light travels towards us from the distant Universe, its path is bent as it passes clumps of matter. Imagine light emitted from two neighboring distant galaxies (see Fig. 1). As these two rays of light traverse the Universe, over billions of light years, they will both pass by the same structures of matter. Every time the paths of the light rays are bent during this journey, the images of those neighboring galaxies that we observe become distorted in the same way. In the most extreme cases, this “gravitational lensing” results in the galaxies being stretched out into long arcs. But in the majority of situations, the lensing effect is more subtle, causing galaxies to appear more elongated, or elliptical, in one direction. This results in an apparent alignment of galaxies in the same part of the sky. The more matter that the light has passed, the stronger the resulting alignment will be. The amount of distortion, and hence alignment, is usually quite small, so to see it we need to take some sort of statistical average of all the distant galaxies in a small patch of sky. With no matter, we would expect to find that our average of randomly oriented galaxies would look like a circle (i.e., with no preferred orientation). With matter, however, we’ll find our average of lensed-aligned galaxies to be an ellipse.

    We can think of the induced galaxy alignment as a faint signature that dark matter has written across the cosmos to tell us exactly where it is and how much of it there is. It’s precisely this signature that the Dark Energy Survey has observed with the 4-meter Blanco telescope in Chile.

    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO/ Victor M Blanco telescope

    In two companion papers, Chang and Vikram and their colleagues present imaging data of a contiguous area of sky spanning 139 square degrees. This is roughly the area of a patch of sky covered by your hand held at arm’s length. By analyzing these images containing 2 million distant galaxies, the researchers are able to map dark matter across this region of space.

    The DES dark matter map is not the first of its kind. Several pioneering analyses have come before it, most notably the Canada-France-Hawaii Telescope [CFHT] Lensing Survey [4], which used 4 times the number of distant galaxies that DES used to map an area of similar size but at higher resolution.

    CFHT Interior

    The two teams have reached the same conclusions, though: The luminous matter that we can see is housed within the dark matter structures that we cannot see, and this dark matter forms a cosmic web of filaments, knots, and voids. As it continues collecting and analyzing data, DES will be able to map how these dark matter structures evolve over time.

    At this point we should address just how challenging this observational measurement is. The change that we wish to detect in galaxy ellipticity induced by the dark matter is of order 1%, an almost imperceptible amount considering the difference between a circle and a line would be a change in ellipticity of 100%. When the light from these distant galaxies reaches Earth, the atmosphere, telescope, and camera induce an additional distortion in the ellipticity of the observed galaxies of the order 10%. Luckily there are stars in our own Milky Way Galaxy that act as point sources, allowing us to model this terrestrial distortion. Much of the painstaking work presented by Vikram and Chang convinces us that the correction that they apply is sufficiently accurate, and furthermore, that the design of DES is optimized to minimize this source of error in their analysis.

    The next few years will be extremely exciting for dark Universe enthusiasts. When the Dark Energy Survey completes its data collection, it will be able to map dark matter over 5000 square degrees using gravitational lensing. Two rival surveys—the European Kilo-Degree Survey [5], and the Hyper-Suprime Camera survey [6]—will both image a smaller area, totaling 1500 square degrees of the cosmos, but with higher precision and depth. These three international collaborations will use their pinpointing of dark matter to confront different cosmological theories that try to explain the mysterious accelerating expansion of our Universe. The acceleration, fueled by dark energy, affects the clumpiness of the dark matter distribution. Mapping mass across cosmic time therefore enables the measurement of dark energy properties at different epochs. A measurement that revealed a time evolution in the dark energy would rule out the current baseline theory that dark energy arises from some universal cosmological constant. The work by Vikram and Chang is just the thrilling start. Expect to see great advances in our understanding as the data collected by these three major new facilities grows.

    This research is published in Physical Review Letters and Physical Review D.


    V. Vikram et al., “Wide-Field Lensing Mass Maps from DES Science Verification Data: Methodology and Detailed Analysis,” Phys Rev. D 92, 022006 (2015).
    C. Chang et al., “Wide-Field Lensing Mass Maps from DES Science Verification Data,” Phys. Rev. Lett. 115, 051301 (2015).
    P. A. R. Ade et al. (Planck Collaboration), “Planck 2015 Results. XIII. Cosmological Parameters,” arXiv:1502.01589.
    L. Van Waerbeke et al., “CFHTLenS: Mapping the Large-Scale Structure with Gravitational Lensing,” Mon. Not. R. Astron. Soc. 433, 3373 (2013).
    J. T. A. de Jong et al., “The Kilo-Degree Survey,” The Messenger 154, 44 (2013).
    S. Miyazaki et al., “Properties of Weak Lensing Clusters Detected on Hyper Suprime-Cam 2.3 Square Degree Field,” Astrophys. J. 807, 22 (2015).

    See the full article here.

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

  • richardmitnick 6:25 pm on July 27, 2015 Permalink | Reply
    Tags: , Dark Energy/Dark Matter, , Pions   

    From livescience: “Dark Pion Particles May Explain Universe’s Invisible Matter” 


    July 25, 2015
    Jesse Emspak

    Researchers propose that dark matter is a kind of invisible, intangible version of a pion, or a type of meson — a category of particles made up of quarks and antiquarks.
    Credit: MichaelTaylor

    Dark matter is the mysterious stuff that cosmologists think makes up some 85 percent of all the matter in the universe. A new theory says dark matter might resemble a known particle. If true, that would open up a window onto an invisible, dark matter version of physics.

    The only way dark matter interacts with anything else is via gravity. If you poured dark matter into a bucket, it would go right through it because it doesn’t react to electromagnetism (one reason you can stand on the ground is because the atoms in your feet are repelled by the atoms in the Earth). Nor does dark matter reflect or absorb light. It’s therefore invisible and intangible.

    Scientists were clued into its existence by the way galaxies behaved. The mass of the galaxies calculated from the visible stuff they contained wasn’t enough to keep them bound to each other. Later, observations of gravitational lensing, in which light bends in the presence of gravity fields, showed there was something that made galaxy clusters more massive that couldn’t be seen.

    Invisible pions

    Now, a team of five physicists has proposed that dark matter might be a kind of invisible, intangible version of a pion, a particle that was originally discovered in the 1930s. A pion is a type of meson — a category of particles made up of quarks and antiquarks; neutral pions travel between protons and neutrons and bind them together into atomic nuclei.

    Most proposals about dark matter assume it is made up of particles that don’t interact with each other much — they pass through each other, only gently touching. The name for such particles is weakly interacting massive particles, or WIMPs. Another idea is that dark matter is made up of axions, hypothetical particles that could solve some unanswered questions about the Standard Model of particle physics.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Axions wouldn’t interact strongly with each other, either.

    The new proposal assumes that the dark matter pions interact much more strongly with each other. When the particles touch, they partially annihilate and turn into normal matter. “It’s a SIMP [strongly interacting massive particle],” said Yonit Hochberg, a postdoctoral researcher at Berkeley and lead author on the study. “Strongly interacting with itself.”

    To annihilate into normal matter, the particles must collide in a “three-to-two” pattern, in which three dark matter particles meet. Some of the dark matter “quarks” that make up the particles annihilate and turn into normal matter, leaving some dark matter behind. With this ratio, the result would leave the right proportion of dark matter to normal matter in the current universe.

    This new explanation suggests that in the early universe the dark pions would have collided with each other, reducing the amount of dark matter. But as the universe expanded the particles would collide less and less often, until now, when they are spread so thinly they hardly ever meet at all.

    The interaction bears a close resemblance to what happens to charged pions in nature. These particles consist of an up quark and an anti-down quark. (Quarks come in six flavors, or types: up, down, top, bottom, charm and strange.) When three pions meet, they partially annihilate and become two pions.

    “[The theory] is based on something similar — something that already happens in nature,” said Eric Kuflik, a postdoctoral researcher at Cornell University in New York and a co-author of the study.

    Different kind of pion

    For the new explanation to work, the dark matter pions would have to be made of something different from normal matter. That’s because anything made of normal quarks simply wouldn’t behave the way dark matter does, at least not in the group’s calculations. (There are theories that strange quarks could make up dark matter).

    Charged pions are made up of an up quark and an anti-down quark, or a down and anti-up quark, while neutral pions are made of an up quark plus an anti-up or a down quark plus an anti-down.

    In the new hypothesis, dark matter pions are made up of dark matter quarks that are held together by dark matter gluons. (Ordinary quarks are held together by normal gluons.) The dark quarks wouldn’t be like the familiar six types, and the dark gluon would, unlike ordinary gluons, have mass, according to the mathematics.

    Dark pions and dwarf galaxies

    Another co-author on the paper, Hitoshi Murayama, professor of physics at the University of California, Berkeley, said the new hypothesis would help explain the density of certain kinds of dwarf galaxies. Computer simulations show dwarf galaxies with very dense center regions, but that isn’t what astronomers see in the sky. “If SIMPs are spread out, the distribution is flatter — it works better,” he said.

    Dan Hooper, a staff scientist at Fermi National Accelerator Laboratory in Illinois, said he isn’t quite convinced that this model of dark matter is necessary to explain the dwarf galaxy conundrum. “There’s a handful of people who say dwarfs don’t look like we expect,” he said. “But do you need some other property to solve that? People have showed it could be the heating of gas.” That is, gas heated at the center of a dwarf galaxy would be less dense.

    The Large Hadron Collider might soon offer some insight into which camp is correct; that strange new “dark pions” are dark matter or that they aren’t and there’s something else. Particle accelerators work by taking atomic nuclei — usually hydrogen but sometimes heavier elements like lead —and smashing them together at nearly the speed of light. The resulting explosion scatters new particles, born of the energy of the collision. In that sense the particles are the “shrapnel.”

    Kuflik said that if there’s “missing” mass (more precisely, mass-energy) from the collision of particles that’s a strong pointer to the kind of dark matter that the researchers are looking for. This is because mass and energy are conserved; if the products of a collision don’t tally up to the same amount of mass and energy you started with, that means there might be a previously unknown particle that escaped detection somewhere.

    Such measurements are hard to do, though, so it will take a lot of sifting through data to see if that happens and what the explanation is.

    Another way to track down dark matter particles might be in a detector made with liquid xenon or germanium, in which electrons would occasionally get knocked off an atom by a passing dark matter particle. There’s already an experiment like that, though, the Large Underground Xenon (LUX) project in South Dakota. It didn’t find anything yet, but it was focused on WIMPs (though it was able to rule out some types). A newer version of the experiment is planned; it might detect other kinds of dark matter particle.

    The team is currently working on a paper outlining the kinds of observations that would detect this kind of dark matter. “We’re currently working on writing up explicit ways these dark pions can interact with ordinary matter,” Hochberg said.

    The study appears in the July 10 issue of the journal Physical Review Letters.

    [The article does not include any deatil as to what sort of equipment was used in this work.]

    See the full article here.

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  • richardmitnick 7:18 am on July 24, 2015 Permalink | Reply
    Tags: , , , Dark Energy/Dark Matter   

    From CAASTRO: “Dark matter halo of dwarf galaxies shaped by supernova feedback” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    21 July 2015
    No Writer Credit


    The Cold Dark Matter (CDM) model has proven very successful, however there exists a long standing problem of ubiquitous ‘cusps’ of dark matter halos, i.e. the dark matter distribution sharply increases to a high value at a central point. Significant improvements in the understanding of detailed physical processes of dark and luminous matter on galactic scales have been achieved by observational data from several galaxy surveys in tandem with advances in cosmological hydrodynamic simulations. These have only been tested in a small number of field galaxies though, owing to the lack of high-quality multi-wavelength data and of standardised analysis tools. In order to provide robust observational constraints to dark matter models, we need to extend the investigation to a larger number of galaxies in a more systematic and consistent manner.

    In a new publication, CAASTRO researcher Dr Se-Heon Oh (ICRAR – University of Western Australia) and colleagues present high-resolution (20-300 pc) mass models of 26 dwarf galaxies and discuss the dark matter distributions near their centres, as part of the LITTLE THINGS survey. This is a high-resolution (~6″ angular; < 2.6 km/s velocity resolution) HI 21cm survey of nearby (< 11 Mpc) gas-rich dwarf galaxies undertaken with the NRAO Very Large Array (VLA) in the northern sky.


    In their publication, the team quantified the degree of the central dark matter concentration of the sample galaxies by measuring the logarithmic inner slopes of their dark matter density profiles. The mean value of the inner slopes (-0.32) indicates a mass distribution with a sizeable constant density-core towards the centres of the galaxies. Comparing these observations with latest Lambda CDM simulations of galaxies where realistic baryonic feedback is included, the dark matter cusps of the halos in both samples can effectively be accounted for by supernova (SN) driven gas outflows.

    Some LITTLE THINGS sample galaxies, however, such as DDO 210, DDO 101 and Haro 29, have relatively steeper inner density slopes. According to the latest hydrodynamic simulations, SN feedback in low mass dwarf galaxies of less than 106 solar masses is not sufficient to disrupt the central cusps, largely due to low star formation efficiencies in these systems. Dr Oh and his team have submitted a Gemini observing proposal for spectroscopy of DDO 210’s inner dark matter halo density profile where simulations have predicted primordial CDM cusps to have survived. This will be a fundamental test for the presence or absence of a signature of the central cusp in low mass halos, and whatever the outcome, will inform the debate on the formation process of low-mass galaxies in particular, as well as provide a crucial test to the LCDM.

    See the full article here.

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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.


    The University of Sydney
    The University of Western Australia
    The University of Melbourne
    Swinburne University of Technology
    The Australian National University
    Curtin University
    University of Queensland

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