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  • richardmitnick 1:09 pm on September 9, 2016 Permalink | Reply
    Tags: Advanced Virgo, , , , Dark Matter, ,   

    From Symmetry: “A tale of two black holes” 

    Symmetry Mag

    Symmetry

    09/09/16
    Liz Kruesi

    1
    LIGO

    The historic detection of gravitational waves announced earlier this year breathed new life into a theory that’s been around for decades: that black holes created in the first second of the universe might make up dark matter. It also inspired a new idea: that those so-called primordial black holes could be contributing to a diffuse background light.

    The connection between these perhaps seemingly disparate areas of astronomy were tied together neatly in a theory from Alexander Kashlinsky, an astrophysicist at NASA’s Goddard Spaceflight Center. And while it’s an unusual idea, as he says, it could be proven true in only a few years.

    Mapping the glow

    Kashlinsky’s focus has been on a residual infrared glow in the universe, the accumulated light of the earliest stars. Unfortunately, all the stars, galaxies and other bright objects in the sky—the known sources of light—oversaturate this diffuse glow. That means that Kashlinsky and his colleagues have to subtract them out of infrared images to find the light that’s left behind.

    They’ve been doing precisely that since 2005, using data from the Spitzer space telescope to arrive at the residual infrared glow: the cosmic infrared background (CIB).

    NASA/Spitzer Telescope
    “NASA/Spitzer Telescope

    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA)
    Cosmic Infrared Background, Credit: Michael Hauser (Space Telescope Science Institute), the COBE/DIRBE Science Team, and NASA

    Other astronomers followed a similar process using Chandra X-ray Observatory data to map the cosmic X-ray background (CXB), the diffuse glow of hotter cosmic material and more energetic sources.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    Cosmic X-ray Background, imagine.gsfc.nasa.gov
    Cosmic X-ray Background, imagine.gsfc.nasa.gov

    In 2013, Kashlinsky and colleagues compared the CIB and CXB and found correlations between the patchy patterns in the two datasets, indicating that something is contributing to both types of background light. So what might be the culprit for both types of light?

    “The only sources that could be coherent across this wide range of wavelengths are black holes,” he says.

    To explain the correlation they found, roughly 1 in 5 of the sources had to be black holes that lived in the first few hundred million years of our universe. But that ratio is oddly large.

    “For comparison,” Kashlinsky says, “in the present populations, we have 1 in 1000 of the emitting sources that are black holes. At the peak of star formation, it’s 1 in 100.”

    He wasn’t sure how the universe could have ever had enough black holes to produce the patterns his team saw in the CIB and CXB. Then the Laser Interferometric Gravitational-wave Observatory (LIGO) discovered a pair of strange beasts: two roughly-30-solar-mass black holes merging and emitting gravitational waves.

    LSC LIGO Scientific Collaboration
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project
    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    A few months later, Kashlinsky saw a study led by Simeon Bird analyzing the possibility that the black holes LIGO had detected were primordial—formed in the universe’s first second. “And it just all came together,” Kashlinsky says.

    Gravitational secrets

    The crucial ripples in space-time picked up by the LIGO detector on September 14, 2015, came from the last dance of two black holes orbiting each other and colliding. One black hole was 36 times the sun’s mass, the other 29 times. Those black-hole weights aren’t easy to make.

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib
    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    The majority of the universe’s black holes are less than about 15 solar masses and form as massive stars collapse at the end of their lives. A black hole weighing 30 solar masses would have to start from a star closer to 100 times our sun’s mass—and nature seems to have a hard time making stars that enormous. To compound the strangeness of the situation, the LIGO detection is from a pair of those black holes. Scientists weren’t expecting such a system, but the universe has a tendency to surprise us.

    Bird and his colleagues from Johns Hopkins University next looked at the possibility that those black holes formed not from massive stars but instead during the universe’s first fractions of a second. Astronomers haven’t yet seen what the cosmos looked like at that time, so they have to rely on theoretical models.

    In all of these models, the early universe exists with density variations. If there were regions of very high-contrasting density, those could have collapsed into black holes in the universe’s first second. If those black holes were at least as heavy as mountains when they formed, they’d stick around until today, dark and seemingly invisible and acting through the gravitational force. And because these primordial black holes formed from density perturbations, they wouldn’t be comprised of protons and neutrons, the particles that make up you, me, stars and, thus, the material that leads to normal black holes.

    All of those characteristics make primordial black holes a tempting candidate for the universe’s mysterious dark matter, which we believe makes up some 25 percent of the universe and reveals itself only through the gravitational force. This possible connection has been around since the 1970s, and astronomers have looked for hints of primordial black holes since. Even though they’ve slowly narrowed down the possibilities, there are a few remaining hiding spots—including the region where the black holes that LIGO detected fall, between about 20 and 1000 solar masses.

    Astronomers have been looking for explanations of what dark matter is for decades. The leading theory is that it’s a new type of particle, but searches keep coming up empty. On the other hand, we know black holes exist; they stem naturally from the theory of gravity.

    “They’re an aesthetically pleasing candidate because they don’t need any new physics,” Bird says.

    A glowing contribution

    Kashlinsky’s newest analysis took the idea of primordial black holes the size that LIGO detected and looked at what that population would do to the diffuse infrared light of the universe. He evolved a model of the early universe, looking at how the first black holes would congregate and grow into clumps. These black holes matched the residual glow of the CIB and, he found, “would be just right to explain the patchiness of infrared background by sources that we measured in the first couple hundred million years of the universe.”

    This theory fits nicely together, but it’s just one analysis of one possible model that came out of an observation of one astrophysical system. Researchers need several more pieces of evidence to say whether primordial black holes are in fact the dark matter. The good news is LIGO will soon begin another observing run that will be able to see black hole collisions even farther away from Earth and thus further back in time. The European gravitational wave observatory VIRGO will also come online in January, providing more data and working in tandem with LIGO.

    VIRGO Collaboration bloc
    VIRGO interferometer EGO Campus
    VIRGO interferometer EGO Campus, in Cascina, Italy

    More cases of gravitational waves from black holes around this 30-solar-masses range could add evidence that there is a population of primordial black holes. Bird and his colleague Ilias Cholis suggest looking for a more unique signal, though, in future gravitational-wave data. For two primordial black holes to become locked in a binary system and merge, they would likely be gravitationally captured during a glancing interaction, which could result in a signal with multiple frequencies or tones at any one moment.

    “This is a rare event, but it would be very characteristic of our scenario,” Cholis says. “In the next 5 to 10 years, we might see one.”

    This smoking-gun signature, as they call it, would be a strong piece of evidence that primordial black holes exist. And if such objects are floating around our universe, it might not be such a stretch to connect them to dark matter.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:02 am on September 8, 2016 Permalink | Reply
    Tags: , Dark Matter, , ,   

    From Don Lincoln for CNN: “Something is wrong with dark matter” 

    1
    CNN

    September 7, 2016

    FNAL Don Lincoln
    Don Lincoln

    Dr. Don Lincoln is a senior physicist at Fermilab and does research using the Large Hadron Collider. He has written numerous books and produces a series of science education videos. He is the author of The Large Hadron Collider: The Extraordinary Story of the Higgs Boson and Other Things That Will Blow Your Mind. Follow him on Facebook. The opinions expressed in this commentary are solely those of the author.

    Nearly a mile under the Black Hills of South Dakota sits a canister of the atomic element xenon, chilled cold enough to turn it to liquid. The canister is the Large Underground Xenon, or LUX, detector — the most sensitive dark matter detector in the world.

    SURF logo
    Sanford Underground levels
    Sanford Underground Research Facility
    LUX Dark matter Experiment at SURF
    LUX Dark matter Experiment at SURF

    But the results of a new analysis by the LUX Collaboration has left scientists perplexed about a substance that has guided the formation of the stars and galaxies since the cosmos began: dark matter.

    Since the 1930s, scientists have known that there was something unexplained about the heavens. Swiss astronomer Fritz Zwicky studied the Coma Cluster, a group of about a thousand galaxies, held together by their mutual gravitational interactions.

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    A map of the Coma cluster. http://www.atlasoftheuniverse.com

    There was only one problem: The galaxies were moving so fast that gravity shouldn’t have been able to hold them together. The cluster should have been ripped apart. In the 1970s, astronomers Vera Rubin and her collaborator Kenneth Ford studied the rotation rates of individual galaxies and came to the same conclusion. There appeared to be no way the observed matter contained in galaxies would generate enough gravity to keep the stars locked in their stately orbits.

    These observations, combined with many other independent lines of evidence, led scientists to consider several possible explanations. These explanations included the possibility that Newton’s familiar laws of motion might be wrong, or that our understanding of gravity needed to be modified. Both these proposals, though, have been largely ruled out.

    Another idea was that there was somehow invisible matter that was generating more gravity. Initial ideas centered on the possibility of black holes, brown dwarf stars or rogue planets roaming the cosmos, but those explanations have also been dismissed. Using a ruthless process of elimination worthy of Sherlock Holmes, astronomers have come to believe the explanation for all of the gravitational anomalies is that there must be some sort of new and undiscovered type of matter in the universe, which Zwicky in 1933 named “dunkle materie,” or dark matter.

    For decades, scientists have tried to work out the properties of dark matter and, while we don’t know everything, we know a lot. From astronomical observations, we know there is five times more dark matter in the universe than all the “billions and billions” of stars and galaxies mentioned in Carl Sagan’s oft-quoted phrase. We also know that dark matter cannot have electrical charge, otherwise it would interact with light and we would have seen it. In fact, by a process of elimination, we know that dark matter is not any known form of matter. It is something new. Of this, scientists are sure.

    However, scientists are less sure about the details.

    For decades now, the most popular theoretical idea was that dark matter was a WIMP, short for weakly interacting massive particle. A WIMP would have a mass in the range of 10 to perhaps 100 times heavier than the familiar proton. It was a particle like a heavy neutron (but definitely not a neutron), massive, electrically neutral, and stable on time scales long compared to the lifetime of the universe.
    The WIMP was popular for two main reasons.

    First, when cosmologists modeled the Big Bang and included WIMPs in the calculation, the WIMPs actively participated in the earliest phases of the birth of the universe but, as the universe expanded and cooled, the space between them grew large enough that they stopped interacting with one another. When scientists calculated how much mass should be tied up in the relic WIMPs, they found it was five times as much mass as ordinary matter, exactly the amount of dark matter seen by astronomers.

    The second reason for the popularity of the WIMP idea is that it explained a mystery in particle physics. The recently discovered Higgs boson has a mass of about 130 times that of the proton. Theoretical considerations predicted a much larger mass, but if a WIMP exists, it is easy to reconcile the prediction and measurement. These two reasons account for the popularity of the WIMP idea and are called “the WIMP miracle.”

    The LUX measurement is simply the most recent and most powerful of a long line of searches for dark matter. They found no evidence for the existence of dark matter and were able to rule out a significant range of possible WIMP properties and masses.

    Now this doesn’t mean the WIMP idea is dead or that dark matter has been disproven. There remain WIMP masses that haven’t been ruled out, and there exist other possible dark matter candidates, including objects called sterile neutrinos, which are possible cousins of the well-known neutrinos generated in nuclear reactors and in the sun. Another recurring proposed dark matter particle is the axion, suggested in the 1970s to explain mysteries in the asymmetry of subatomic processes. (Although neither sterile neutrinos, nor axions, have been observed).

    Nobody knows what the final answer will be. That’s why we do research. But there is no question that there is a mystery in the cosmos. Galaxies don’t act as we expect. The LUX measurement is a powerful new bit of information for astronomers to consider and has added to the general confusion, forcing scientists to take another look at ideas other than WIMPs.

    All this reminds me of the old Buffalo Springfield song: “There’s something happening here. What it is ain’t exactly clear …”

    See the full article here .

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  • richardmitnick 10:58 am on September 7, 2016 Permalink | Reply
    Tags: , , Dark Matter,   

    From U Cambridge: “Massive holes ‘punched’ through a trail of stars likely caused by dark matter” 

    U Cambridge bloc

    Cambridge University

    07 Sep 2016
    Sarah Collins
    sarah.collins@admin.cam.ac.uk

    1
    Artist’s impression of dark matter clumps around a Milky Way-like galaxy. Credit: V. Belokurov, D. Erkal, S.E. Koposov (IoA, Cambridge). Photo: Colour image of M31 from Adam Evans.

    The discovery of two massive holes punched through a stream of stars could help answer questions about the nature of dark matter, the mysterious substance holding galaxies together.

    Researchers have detected two massive holes which have been ‘punched’ through a stream of stars just outside the Milky Way, and found that they were likely caused by clumps of dark matter, the invisible substance which holds galaxies together and makes up a quarter of all matter and energy in the universe.

    The scientists, from the University of Cambridge, found the holes by studying the distribution of stars in the Milky Way. While the clumps of dark matter that likely made the holes are gigantic in comparison to our Solar System – with a mass between one million and 100 million times that of the Sun – they are actually the tiniest clumps of dark matter detected to date.

    The results, which have been submitted to the Monthly Notices of the Royal Astronomical Society, could help researchers understand the properties of dark matter, by inferring what type of particle this mysterious substance could be made of. According to their calculations and simulations, dark matter is likely made up of particles more massive and more sluggish than previously thought, although such a particle has yet to be discovered.

    “While we do not yet understand what dark matter is formed of, we know that it is everywhere,” said Dr Denis Erkal from Cambridge’s Institute of Astronomy, the paper’s lead author. “It permeates the universe and acts as scaffolding around which astrophysical objects made of ordinary matter – such as galaxies – are assembled.”

    Current theory on how the universe was formed predicts that many of these dark matter building blocks have been left unused, and there are possibly tens of thousands of small clumps of dark matter swarming in and around the Milky Way. These small clumps, known as dark matter sub-haloes, are completely dark, and don’t contain any stars, gas or dust.

    Dark matter cannot be directly measured, and so its existence is usually inferred by the gravitational pull it exerts on other objects, such as by observing the movement of stars in a galaxy. But since sub-haloes don’t contain any ordinary matter, researchers need to develop alternative techniques in order to observe them.

    The technique the Cambridge researchers developed was to essentially look for giant holes punched through a stream of stars. These streams are the remnants of small satellites, either dwarf galaxies or globular clusters, which were once in orbit around our own galaxy, but the strong tidal forces of the Milky Way have torn them apart. The remnants of these former satellites are often stretched out into long and narrow tails of stars, known as stellar streams.

    “Stellar streams are actually simple and fragile structures,” said co-author Dr Sergey Koposov. “The stars in a stellar stream closely follow one another since their orbits all started from the same place. But they don’t actually feel each other’s presence, and so the apparent coherence of the stream can be fractured if a massive body passes nearby. If a dark matter sub-halo passes through a stellar stream, the result will be a gap in the stream which is proportional to the mass of the body that created it.”

    The researchers used data from the stellar streams in the Palomar 5 globular cluster to look for evidence of a sub-halo fly-by. Using a new modelling technique, they were able to observe the stream with greater precision than ever before. What they found was a pair of wrinkled tidal tails, with two gaps of different widths.

    By running thousands of computer simulations, the researchers determined that the gaps were consistent with a fly-by of a dark matter sub-halo. If confirmed, these would be the smallest dark matter clumps detected to date.

    “If dark matter can exist in clumps smaller than the smallest dwarf galaxy, then it also tells us something about the nature of the particles which dark matter is made of – namely that it must be made of very massive particles,” said co-author Dr Vasily Belokurov. “This would be a breakthrough in our understanding of dark matter.”

    The reason that researchers can make this connection is that the mass of the smallest clump of dark matter is closely linked to the mass of the yet unknown particle that dark matter is composed of. More precisely, the smaller the clumps of dark matter, the higher the mass of the particle.

    Since we do not yet know what dark matter is made of, the simplest way to characterise the particles is to assign them a particular energy or mass. If the particles are very light, then they can move and disperse into very large clumps. But if the particles are very massive, then they can’t move very fast, causing them to condense – in the first instance – into very small clumps.

    “Mass is related to how fast these particles can move, and how fast they can move tells you about their size,” said Belokurov. “So that’s why it’s so interesting to detect very small clumps of dark matter, because it tells you that the dark matter particle itself must be very massive.”

    “If our technique works as predicted, in the near future we will be able to use it to discover even smaller clumps of dark matter,” said Erkal. “It’s like putting dark matter goggles on and seeing thousands of dark clumps each more massive than a million suns whizzing around.”

    See the full article here .

    Please help promote STEM in your local schools.

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    U Cambridge Campus

    The University of Cambridge (abbreviated as Cantab in post-nominal letters) is a collegiate public research university in Cambridge, England. Founded in 1209, Cambridge is the second-oldest university in the English-speaking world and the world’s fourth-oldest surviving university. It grew out of an association of scholars who left the University of Oxford after a dispute with townsfolk. The two ancient universities share many common features and are often jointly referred to as “Oxbridge”.

    Cambridge is formed from a variety of institutions which include 31 constituent colleges and over 100 academic departments organised into six schools. The university occupies buildings throughout the town, many of which are of historical importance. The colleges are self-governing institutions founded as integral parts of the university. In the year ended 31 July 2014, the university had a total income of £1.51 billion, of which £371 million was from research grants and contracts. The central university and colleges have a combined endowment of around £4.9 billion, the largest of any university outside the United States. Cambridge is a member of many associations and forms part of the “golden triangle” of leading English universities and Cambridge University Health Partners, an academic health science centre. The university is closely linked with the development of the high-tech business cluster known as “Silicon Fen”.

     
  • richardmitnick 8:08 am on September 6, 2016 Permalink | Reply
    Tags: , , Dark Matter,   

    From Ethan Siegel: “Dark matter riches?” 

    9.5.16
    From Ethan Siegel

    1
    An image of galaxy Dragonfly 44, recently discovered to have the largest offset between normal matter and dark matter of any known, large galaxy. Image credit: Pieter van Dokkum, Roberto Abraham, Gemini Observatory/AURA.

    Dragonfly 44 It was discovered just last year when the Dragonfly Telephoto Array observed a region of the sky in the constellation Coma.

    U Toronto Dunlap Dragonfly telescope Array
    U Toronto Dunlap Dragonfly telescope Array

    How we know some galaxies have more than others.

    “Motions of the stars tell you how much matter there is. They don’t care what form the matter is, they just tell you that it’s there.” -Pieter van Dokkum

    One of the biggest surprises about galaxies in our Universe is that stars only make up a tiny fraction of their mass.

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    Traceable stars, neutral gas, and (even farther out) globular clusters all point to the existence of dark matter, which has mass but exists in a large, diffuse halo well beyond the normal matter’s location. Image credit: Wikimedia Commons user Stefania.deluca.

    Looking to gas, dust, plasma, black holes and other non-luminous forms fails to account for what’s missing.

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    From simulations and inferred maps, dark matter (blue) may form some clumps, but overall exists in a massive, diffuse halo around the luminous, disk-like part of galaxies we’re familiar with. Image credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI).

    For that, you need dark matter, which has mass but is completely invisible to all non-gravitational interactions.

    Dark matter, in a 5:1 ratio to normal matter, accounts for everything from the formation of the largest cosmic structures to galaxies’ internal motions to the fluctuation patterns in the cosmic microwave background.

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    The fluctuations across the entire sky in the cosmic microwave background, the Big Bang’s leftover glow. Image credit: ESA and the Planck collaboration.

    Present in a large, diffuse halo surrounding galaxies and clusters, its gravity is observable even when collisions separate out the normal matter.

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    Four colliding galaxy clusters, showing the separation between X-rays (pink) and gravitation (blue), indicative of dark matter. Images credit: X-ray: NASA/CXC/UVic./A.Mahdavi et al. Optical/Lensing: CFHT/UVic./A. Mahdavi et al. (top left); X-ray: NASA/CXC/UCDavis/W.Dawson et al.; Optical: NASA/ STScI/UCDavis/ W.Dawson et al. (top right); ESA/XMM-Newton/F. Gastaldello (INAF/ IASF, Milano, Italy)/CFHTLS (bottom left); X-ray: NASA, ESA, CXC, M. Bradac (University of California, Santa Barbara), and S. Allen (Stanford University) (bottom right).

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    CFHT Telescope, Mauna Kea, Hawaii, USA
    CFHT Interior
    CFHT Telescope, Mauna Kea, Hawaii, USA

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    ESA/XMM Newton
    ESA/XMM Newton

    The smallest galaxies are richer in dark matter, as episodes of star formation expel the normal matter.

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    Galaxies undergoing massive bursts of star formation expel large quantities of matter at great speeds. In low-mass galaxies, this material easily escapes the galaxy’s gravitational pull. Image credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA), of the Cigar Galaxy, Messier 82.

    What’s left behind is mostly dark.

    The lowest-mass galaxy known, Segue 3, has 600 times more dark matter than normal matter.

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    Only approximately 1000 stars are present in the entirety of dwarf galaxy Segue 3, which has a gravitational mass of 600,000 Suns. Image credit: Marla Geha and Keck Observatories, of the stars making up the dwarf satellite Segue 1.

    Keck Observatory, Mauna Kea, Hawaii, USA
    Keck Observatory Interior
    Keck Observatory, Mauna Kea, Hawaii, USA

    But large galaxies can lose their normal matter too, by speeding through the intergalactic medium.

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    A Hubble (visible light) and Chandra (X-ray) composite of galaxy ESO 137–001 as it speeds through the intergalactic medium, becoming stripped of stars and gas, while its dark matter remains intact. Image credit: NASA, ESA, CXC.

    Recently, the galaxy Dragonfly 44 has surprised astronomers with its dark matter richness.

    8
    If their normal matter was stripped away, perhaps these “dark galaxies” weren’t always so dark.

    See the full article here .

    Please help promote STEM in your local schools.

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 3:34 pm on August 30, 2016 Permalink | Reply
    Tags: , , , Dark Matter, ,   

    From Symmetry: “Our galactic neighborhood” 

    Symmetry Mag

    Symmetry

    08/30/16
    Molly Olmstead

    What can our cosmic neighbors tell us about dark matter and the early universe?

    Milky Way NASA/JPL-Caltech /ESO R. Hurt
    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Imagine a mansion.

    Now picture that mansion at the heart of a neighborhood that stretches irregularly around it, featuring other houses of different sizes—but all considerably smaller. Cloak the neighborhood in darkness, and the houses appear as clusters of lights. Many of the clusters are bright and easy to see from the mansion, but some can just barely be distinguished from the darkness.

    This is our galactic neighborhood. The mansion is the Milky Way, our 100,000-light-years-across home in the universe. Stretching roughly a million light years from the center of the Milky Way, our galactic neighborhood is composed of galaxies, star clusters and large roving gas clouds that are gravitationally bound to us.

    The largest satellite galaxy, the Large Magellanic Cloud [LMC], is also one of the closest.

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    LMC

    It is visible to the naked eye from areas clear of light pollution in the Southern Hemisphere. If the Large Magellanic Cloud were around the size of the average American home—about 2,500 square feet—then by a conservative estimate the Milky Way mansion would occupy more than a full city block. On that scale, our most diminutive neighbors would occupy the same amount of space as a toaster.

    Our cosmic neighbors promise answers to questions about hidden matter and the ancient universe. Scientists are setting out to find them.

    What makes a neighbor

    If we are the mansion, the neighboring houses are dwarf galaxies. Scientists have identified about 50 possible galaxies orbiting the Milky Way and have confirmed the identities of roughly 30 of them. These galaxies range in size from several billion stars to only a few hundred. For perspective, the Milky Way contains somewhere between 100 billion to a trillion stars.

    Dwarf galaxies are the most dark-matter-dense objects known in the universe. In fact, they have far more dark matter than regular matter. Segue 1, our smallest confirmed neighbor, is made of 99.97 percent dark matter.

    Dark matter is key to galaxy formation. A galaxy forms when enough regular matter is attracted to a single area by the gravitational pull of a clump of dark matter.

    Dark matter halo  Image credit: Virgo consortium / A. Amblard / ESA
    Dark matter halo Image credit: Virgo consortium / A. Amblard / ESA

    Projects such as the Dark Energy Survey, or DES, find these galaxies by snapping images of a segment of the sky with a powerful telescope camera. Scientists analyze the resulting images, looking for the pattern of color and brightness characteristic of galaxies.

    Dark Energy Icon
    Dark Energy Camera,  built at FNAL
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile
    Dark Energy Camera, built at FNAL; NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile

    Scientists can find dark matter clumps by measuring the motion and chemical composition of stars. If a smaller galaxy seems to be behaving like a more massive galaxy, observers can conclude a considerable amount of dark matter must anchor the galaxy.

    “Essentially, they are nearby clouds of dark matter with just enough stars to detect them,” says Keith Bechtol, a postdoctoral researcher at the University of Wisconsin-Madison and a member of the Dark Energy Survey.

    Through these methods of identification (and thanks to the new capabilities of digital cameras), the Sloan Digital Sky Survey kicked off the modern hunt for dwarf galaxies in the early 2000s.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    The survey, which looked at the northern part of the sky, more than doubled the number of known satellite dwarf galaxies from 11 to 26 galaxies between 2005 and 2010.

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey
    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Now DES, along with some other surveys, is leading the search. In the last few years DES and its Dark Energy Camera, which maps the southern part of the sky, brought the total to 50 probable galaxies.

    Dark matter mysteries

    Dwarf galaxies serve as ideal tools for studying dark matter. While scientists haven’t yet directly discovered dark matter, in studying dwarf galaxies they’ve been able to draw more and more conclusions about how it behaves and, therefore, what it could be.

    “Dwarf galaxies tell us about the small-scale structure of how dark matter clumps,” says Alex Drlica-Wagner of Fermi National Accelerator Laboratory, one of the leaders of the DES analysis. “They are excellent probes for cosmology at the smallest scales.”

    Dwarf galaxies also present useful targets for gamma-ray telescopes, which could tell us more about how dark matter particles behave.

    NASA/Fermi Telescope
    NASA/Fermi Gamma-ray Telescope

    ESA/Integral
    ESA/Integral Gamma-ray telescope

    Some models posit that dark matter is its own antiparticle. If that were so, it could annihilate when it meets other dark matter particles, releasing gamma rays. Scientists are looking for those gamma rays.

    But while studying these neighbors provides clues about the nature of dark matter, they also raise more and more questions. The prevailing cosmological theory of dark matter has accurately described much of what scientists observe in the universe. But when scientists looked to our neighbors, some of the predictions didn’t hold up.

    The number of galaxies appears to be lower than expected from calculations, for example, and those that are around seem to be too small. While some of the solutions to these problems may lie in the capabilities of the telescopes or the simulations themselves, we may also need to reconsider the way we think dark matter interacts.

    The elements of the neighborhood

    Dwarf galaxies don’t just tell us about dark matter: They also present a window into the ancient past. Most dwarf galaxies’ stars formed more than 10 billion years ago, not long after the Big Bang. Our current understanding of galaxy formation, according to Bechtol, is that after small galaxies formed, some of them merged over billions of years into larger galaxies.

    If we didn’t have these ancient neighbors, we’d have to peer all the way across the universe to see far enough back in time to glimpse galaxies that formed soon after the big bang. While the Milky Way and other large galaxies bustle with activity and new star formation, the satellite galaxies remain mostly static—snapshots of galaxies soon after their birth.

    “They’ve mostly been sitting there, waiting for us to study them,” says Josh Simon, an astronomer at the Carnegie Institution for Science.

    The abundance of certain elements in stars in dwarf galaxies can tell scientists about the conditions and mechanisms that produce them. Scientists can also look to the elements to learn about even older stars.

    The first generation of stars are thought to have looked very different than those formed afterward. When they exploded as supernovae, they released new elements that would later appear in stars of the next generation, some of which are found in our neighboring galaxies.

    “They do give us the most direct fingerprint we can get as to what those first stars might have been like,” Simon says.

    Scientists have learned a lot about our satellites in just the past few years, but there’s always more to learn. DES will begin its fourth year of data collection in August. Several other surveys are also underway. And the Large Synoptic Survey Telescope, an ambitious international project currently under construction in Chile, will begin operating fully in 2022.

    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST/Camera, built at SLAC; SST telescope, currently under construction at Cerro Pachón Chile

    LSST will create a more detailed map than any of the previous surveys’ combined.

    From NatGeo, Inside the Milky Way, possibly the best science video ever made.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:59 am on August 26, 2016 Permalink | Reply
    Tags: , , , Dark Matter, New Efforts to Identify Dark Matter   

    From AAS NOVA: “New Efforts to Identify Dark Matter” 

    AASNOVA

    American Astronomical Society

    26 August 2016
    Susanna Kohler

    1
    The dark matter of the universe forms the basis for the formation of galaxies. But what is this dark matter made of? [AMNH]

    Could the dark matter in our universe be “warm” instead of “cold”? Recent observations have placed new constraints on the warm dark matter model.

    What’s the Deal with Cold/Warm/Hot Dark Matter?

    2
    An example of cold dark matter: MACHOs, massive objects like black holes that are hiding in the halo of our galaxy. [Alain r]

    Nobody knows what dark matter is made of, but we have a few theories. The objects or particles that could make up dark matter fall into three broad categories — cold, warm, and hot dark matter — based on something called their “free streaming length,” or how far they moved due to random motions in the early universe.

    Neutrinos are an example of hot dark matter: very light particles with free streaming lengths much longer than the size of a typical galaxy. Cold dark matter could consist of objects like black holes or brown dwarfs, or particles like WIMPs — all of which are very heavy and therefore have free streaming lengths much shorter than the size of a galaxy.

    Warm dark matter is what’s in between: middle-mass particles with free streaming lengths roughly the size of a galaxy. There aren’t any known particles that fit this description, but there are theorized particles such as sterile neutrinos or gravitinos that do.

    3
    Cumulative mass functions at z = 6 for different values of the warm dark matter particle mass mX. The shaded boxs on the left correspond to the observed number density of faint galaxies within different confidence levels. [Menci et al. 2016]

    Smoothing Out the Universe

    The widely favored model is lambda-CDM, in which cold dark matter makes up the missing matter in our universe. This model nicely explains much of what we observe, but it still has a few problems. The biggest issue with lambda-CDM is that it predicts that there should be many more small, dwarf galaxies than we observe.

    While this could just mean that we haven’t yet managed to see all the existing, faint dwarf galaxies, we should also consider alternative models — the warm dark matter model chief among them.

    In the early universe, small density perturbations on sub-galactic scales produce dwarf galaxies in the lambda-CDM model. But in the warm dark matter model, the longer free streaming length of the dark matter particles smooth out some of those small perturbations. This results in the formation of fewer dwarf galaxies — which fits better with our current observations.

    Limits on Warm Dark Matter

    So how can we test this alternative model? The maximum number density of dark-matter halos predicted by the warm dark matter model at a given redshift depends on the mass of the candidate dark matter particle: a larger particle mass means that more halos form. We therefore can set lower limits on the mass of dark matter particles in a two-step process:

    1. Calculate the maximum number density of dark matter halos predicted by models, and
    2. Compare this to the measured abundance of the faintest galaxies at a given redshift.

    4
    Another way of looking at it: for different values of the dark matter particle mass mX, this shows the maximum number density of dark matter halos predicted at z = 6. The shaded areas represent the observed number density of faint galaxies at different confidence levels. [Menci et al. 2016]

    Recently, unprecedented new Hubble observations of ultra-faint, lensed galaxies in the Hubble Frontier Fields at z~6 have allowed for the discovery of more faint galaxies at this redshift than ever before. Now, a team of scientists led by Nicola Menci (INAF Rome) have used these observations to set a new limit on the lowest mass that candidate dark matter particles can have.

    Menci and collaborators find that these new observations constrain the particle masses to be above 2.9 keV at the 1σ confidence level. These constitute the tightest constraints on the mass of candidate warm dark matter particles derived to date, and they even allow us to rule out some production mechanisms for theorized particles.

    Extending this analysis to other clusters with deep observations will only improve the constraints, bringing us ever closer to understanding what dark matter is made of.

    Citation

    N. Menci et al 2016 ApJ 825 L1. doi:10.3847/2041-8205/825/1/L1

    See the full article here .

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  • richardmitnick 2:50 pm on August 25, 2016 Permalink | Reply
    Tags: , , , Dark Matter, ,   

    From JHU: “Can one cosmic enigma help solve another? Johns Hopkins researchers think so” 

    Johns Hopkins
    Johns Hopkins University

    8.24.16
    Arthur Hirsch

    1
    Image credit: VectaRay

    2
    A massive cluster of yellowish galaxies, seemingly caught in a red and blue spider web of eerily distorted background galaxies, makes for a spellbinding picture from the new Advanced Camera for Surveys aboard NASA’s Hubble Space Telescope. To make this unprecedented image of the cosmos, Hubble peered straight through the center of one of the most massive galaxy clusters known, called Abell 1689. 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 the galaxies located far behind it. Some of the faintest objects in the picture are probably over 13 billion light-years away (redshift value 6). Strong gravitational lensing as observed by the Hubble Space Telescope in Abell 1689 indicates the presence of dark matter. Credit: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA. phys.org.

    Astrophysicists from Johns Hopkins University have proposed a clever new way of shedding light on the mysterious dark matter believed to make up most of the universe. The irony is they want to try to pin down the nature of this unexplained phenomenon by using another obscure cosmic emanation known as “fast radio bursts.”

    In a paper published today in Physical Review Letters, the team of astrophysicists argues that these extremely bright and brief flashes of radio-frequency radiation can provide clues about whether certain black holes are dark matter.

    Julian Muñoz, a Johns Hopkins graduate student and the paper’s lead author, said fast radio bursts, or FRBs, provide a direct and specific way of detecting black holes of a specific mass, which are the suspect dark matter.

    FRB Fast Radio Bursts from NAOJ Subaru
    FRB Fast Radio Bursts from NAOJ Subaru, Mauna Key, Hawaii, USA

    Muñoz wrote the paper along with Ely D. Kovetz, a post-doctoral fellow; Marc Kamionkowski, a professor in the Department of Physics and Astronomy; and Liang Dai, who completed his doctorate in astrophysics at Johns Hopkins last year. Dai is now a NASA Einstein Postdoctoral Fellow at the Institute for Advanced Study in Princeton, New Jersey.

    The paper builds on a hypothesis offered in a paper published this spring by Muñoz, Kovetz, and Kamionkowski, along with five Johns Hopkins colleagues. Also published in Physical Review Letters, that research made a speculative case that the collision of black holes detected early in the year by the Laser Interferometer Gravitational-Wave Observatory, or LIGO, was actually dark matter, a substance that makes up 85 percent of the mass of the universe.

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib
    Credit: MPI for Gravitational Physics/W.Benger-Zib
    LSC LIGO Scientific Collaboration
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    The earlier paper made what Kamionkowski called a “plausibility argument” that LIGO found dark matter. The study took as a point of departure the fact that the objects detected by LIGO fit within the predicted range of mass of so-called “primordial” black holes. Unlike black holes that formed from imploded stars, primordial black holes are believed to have formed from the collapse of large expanses of gas during the birth of the universe.

    The existence of primordial black holes has not been established with certainty, but they have been suggested before as a possible solution to the riddle of dark matter. With so little evidence of them to examine, the hypothesis had not gained a large following among scientists.

    The earlier paper made what Kamionkowski called a “plausibility argument” that LIGO found dark matter. The study took as a point of departure the fact that the objects detected by LIGO fit within the predicted range of mass of so-called “primordial” black holes. Unlike black holes that formed from imploded stars, primordial black holes are believed to have formed from the collapse of large expanses of gas during the birth of the universe.

    The LIGO findings, however, raised the prospect anew, especially as the objects detected in that experiment conform to the mass predicted for dark matter.

    The Johns Hopkins team calculated how often these primordial black holes would form binary pairs, and eventually collide. Taking into account the size and elongated shape believed to characterize primordial black hole binary orbits, the team came up with a collision rate that conforms to the LIGO findings.

    Key to the argument is that the black holes that LIGO detected fall within a range of 29 to 36 solar masses, meaning they are that many times greater than the mass of the sun. The new paper considers the question of how to test the hypothesis that dark matter consists of black holes of roughly 30 solar masses.

    That’s where the fast radio bursts come in. First observed only a few years ago, these flashes of radio frequency radiation emit intense energy, but last only fractions of a second. Their origins are unknown but are believed to lie in galaxies outside the Milky Way.

    If the speculation about their origins is true, Kamionkowski said, the radio waves would travel great distances before they’re observed on Earth, perhaps passing a black hole. According to Einstein’s theory of general relativity, the ray would be deflected when it passes a black hole. If it passes close enough, it could be split into two rays shooting off in the same direction—creating two images from one source.

    The new study shows that if the black hole has 30 times the mass of the Sun, the two images will arrive a few milliseconds apart. If 30-solar-mass black holes make up the dark matter, there is a chance that any given fast radio burst will be deflected in this way and followed in a few milliseconds by an echo.

    “The echoing of FRBs is a very direct probe of dark matter,” Muñoz said. “While gravitational waves might ‘indicate’ that dark matter is made of black holes, there are other ways to produce very-massive black holes with regular astrophysics, so it would be hard to convince oneself that we are detecting dark matter. However, gravitational lensing of fast radio bursts has a very unique signature, with no other astrophysical phenomenon that could reproduce it.”

    Kaimonkowski said that while the probability for any such FRB echo is small, “it is expected that several of the thousands of FRBs to be detected in the next few years will have such echoes … if black holes make up the dark matter.”

    So far, only about 20 fast radio bursts have been detected and recorded since 2001. The very sensitive instruments needed to detect them can look at only very small slices of the sky at a time, limiting the rate at which the bursts can be found. A new telescope expected to go into operation this year that seems particularly promising for spotting radio bursts is the Canadian Hydrogen Intensity Mapping Experiment. The joint project of the University of British Columbia, McGill University, the University of Toronto, and the Dominion Radio Astrophysical Observatory stands in British Columbia.

    “Once the thing is working up to their planned specifications, they should collect enough FRBs to begin the tests we propose,” said Kamionkowski, estimating results could be available in three to five years.

    See the full article here .

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    Johns Hopkins Campus

    The Johns Hopkins University opened in 1876, with the inauguration of its first president, Daniel Coit Gilman. “What are we aiming at?” Gilman asked in his installation address. “The encouragement of research … and the advancement of individual scholars, who by their excellence will advance the sciences they pursue, and the society where they dwell.”

    The mission laid out by Gilman remains the university’s mission today, summed up in a simple but powerful restatement of Gilman’s own words: “Knowledge for the world.”

    What Gilman created was a research university, dedicated to advancing both students’ knowledge and the state of human knowledge through research and scholarship. Gilman believed that teaching and research are interdependent, that success in one depends on success in the other. A modern university, he believed, must do both well. The realization of Gilman’s philosophy at Johns Hopkins, and at other institutions that later attracted Johns Hopkins-trained scholars, revolutionized higher education in America, leading to the research university system as it exists today.

     
  • richardmitnick 1:57 pm on August 25, 2016 Permalink | Reply
    Tags: , , Dark galaxy Dragonfly 44, Dark Matter, , ,   

    From Keck: “Scientists Discover Massive Galaxy Made of 99.99 Percent Dark Matter” 

    Keck Observatory

    August 25, 2016

    SCIENCE CONTACT
    Pieter van Dokkum
    Yale University
    New Haven, Connecticut, USA
    Tel: +1-203-432-3000
    E-mail: pieter.vandokkum@yale.edu

    MEDIA CONTACT

    Steve Jefferson
    W. M. Keck Observatory
    (808) 881-3827
    sjefferson@keck.hawaii.edu

    Keck Observatory.
    Keck, with Subaru and IRTF (NASA Infrared Telescope Facility). Vadim Kurland

    Keck Observatory

    1
    The dark galaxy Dragonfly 44. The image on the left is a wide view of the galaxy taken with the Gemini North telescope using the Gemini Multi-Object Spectrograph (GMOS). The close-up on the right is from the same very deep image, revealing the large, elongated galaxy, and halo of spherical clusters of stars around the galaxy’s core, similar to the halo that surrounds our Milky Way Galaxy. Dragonfly 44 is very faint for its mass, and consists almost entirely of Dark Matter. Credit: Pieter van Dokkum, Roberto Abraham, Gemini; Sloan Digital Sky Survey.

    Using the world’s most powerful telescopes, an international team of astronomers has discovered a massive galaxy that consists almost entirely of Dark Matter. Using the W. M. Keck Observatory and the Gemini North telescope – both on Maunakea, Hawaii – the team found a galaxy whose mass is almost entirely Dark Matter. The findings are being published in The Astrophysical Journal Letters today.

    Gemini/North telescope at Manua Kea, Hawaii, USA
    GEMINI/North GMOS
    Gemini/North telescope at Manua Kea, Hawaii, USA; GEMINI/North GMOS

    Even though it is relatively nearby, the galaxy, named Dragonfly 44, had been missed by astronomers for decades because it is very dim. It was discovered just last year when the Dragonfly Telephoto Array observed a region of the sky in the constellation Coma.

    U Toronto Dunlap Dragonfly telescope Array
    U Toronto Dunlap Dragonfly telescope Array

    Upon further scrutiny, the team realized the galaxy had to have more than meets the eye: it has so few stars that it quickly would be ripped apart unless something was holding it together.

    To determine the amount of Dark Matter in Dragonfly 44, astronomers used the DEIMOS instrument installed on Keck II to measure the velocities of stars for 33.5 hours over a period of six nights so they could determine the galaxy’s mass.

    Keck/DEIMOS
    Keck/DEIMOS

    The team then used the Gemini Multi-Object Spectrograph (GMOS) on the 8-meter Gemini North telescope on Maunakea in Hawaii to reveal a halo of spherical clusters of stars around the galaxy’s core, similar to the halo that surrounds our Milky Way Galaxy.

    “Motions of the stars tell you how much matter there is, van Dokkum said. “They don’t care what form the matter is, they just tell you that it’s there. In the Dragonfly galaxy stars move very fast. So there was a huge discrepancy: using Keck Observatory, we found many times more mass indicated by the motions of the stars, then there is mass in the stars themselves.”

    The mass of the galaxy is estimated to be a trillion times the mass of the Sun – very similar to the mass of our own Milky Way galaxy. However, only one hundredth of one percent of that is in the form of stars and “normal” matter; the other 99.99 percent is in the form of dark matter. The Milky Way has more than a hundred times more stars than Dragonfly 44.

    Finding a galaxy with the mass of the Milky Way that is almost entirely dark was unexpected. “We have no idea how galaxies like Dragonfly 44 could have formed,” Roberto Abraham, a co-author of the study, said. “The Gemini data show that a relatively large fraction of the stars is in the form of very compact clusters, and that is probably an important clue. But at the moment we’re just guessing.”

    “This has big implications for the study of Dark Matter,” van Dokkum said. “It helps to have objects that are almost entirely made of Dark Matter so we don’t get confused by stars and all the other things that galaxies have. The only such galaxies we had to study before were tiny. This finding opens up a whole new class of massive objects that we can study.

    “Ultimately what we really want to learn is what Dark Matter is,” van Dokkum said. “The race is on to find massive dark galaxies that are even closer to us than Dragonfly 44, so we can look for feeble signals that may reveal a Dark Matter particle.”

    Additional co-authors are Shany Danieli, Allison Merritt, and Lamiya Mowla of Yale, Jean Brodie of the University of California Observatories, Charlie Conroy of Harvard, Aaron Romanowsky of San Jose State University, and Jielai Zhang of the University of Toronto.

    The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes near the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrographs and world-leading laser guide star adaptive optics systems.

    DEIMOS (DEep Imaging Multi-Object Spetrograph) boasts the largest field of view (16.7 arcmin by 5 arcmin) of any of the Keck Observatory instruments, and the largest number of pixels (64 Mpix). It is used primarily in its multi-object mode, obtaining simultaneous spectra of up to 130 galaxies or stars. Astronomers study fields of distant galaxies with DEIMOS, efficiently probing the most distant corners of the universe with high sensitivity.

    See the full article here .

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    Mission
    To advance the frontiers of astronomy and share our discoveries with the world.

    The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometer and world-leading laser guide star adaptive optics systems. Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

    Today Keck Observatory is supported by both public funding sources and private philanthropy. As a 501(c)3, the organization is managed by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California, with liaisons to the board from NASA and the Keck Foundation.
    Keck UCal

    Keck NASA

    Keck Caltech

     
  • richardmitnick 4:14 pm on August 10, 2016 Permalink | Reply
    Tags: , , Dark Matter, ,   

    From Symmetry: “Dark matter hopes dwindle with X-ray signal” 

    Symmetry Mag

    Symmetry

    08/10/16
    Manuel Gnida

    A previously detected, anomalously large X-ray signal is absent in new Hitomi satellite data, setting tighter limits for a dark matter interpretation.

    1
    Hitomi collaboration; NASA/CXC; Greg Stewart

    In the final data sent by the Hitomi spacecraft, a surprisingly large X-ray signal previously seen emanating from the Perseus galaxy cluster did not appear.

    JAXA/Hitomi telescope
    JAXA/Hitomi telescope

    This casts a shadow over previous speculation that the anomalously bright signal might have come from dark matter.

    “We would have been able to see this signal much clearer with Hitomi than with other satellites,” says Norbert Werner from the Kavli Institute for Particle Astrophysics and Cosmology, a joint institute of Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

    “However, there is no unidentified X-ray line at the high flux level found in earlier studies.”

    Werner and his colleagues from the Hitomi collaboration report their findings in a paper submitted to The Astrophysical Journal Letters.

    The mysterious signal was first discovered with lower flux in 2014 when researchers looked at the superposition of X-ray emissions from 73 galaxy clusters recorded with the European XMM-Newton satellite.

    ESA/XMM Newton
    ESA/XMM Newton

    These stacked data increase the sensitivity to signals that are too weak to be detected in individual clusters.

    The scientists found an unexplained X-ray line at an energy of about 3500 electronvolts (3.5 keV), says Esra Bulbul from the MIT Kavli Institute for Astrophysics and Space Research, the lead author of the 2014 study and a co-author of the Hitomi paper.

    “After careful analysis we concluded that it wasn’t caused by the instrument itself and that it was unlikely to be caused by any known astrophysical processes,” she says. “So we asked ourselves ‘What else could its origin be?’”

    One interpretation of the so-called 3.5-keV line was that it could be caused by hypothetical dark matter particles called sterile neutrinos decaying in space.

    Yet, there was something bizarre about the 3.5-keV line. Bulbul and her colleagues found it again in data taken with NASA’s Chandra X-ray Observatory from just the Perseus cluster.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    But in the Chandra data, the individual signal was inexplicably strong—about 30 times stronger than it should have been according to the stacked data.

    Adding to the controversy was the fact that some groups saw the X-ray line in Perseus and other objects using XMM-Newton, Chandra and the Japanese Suzaku satellite, while others using the same instruments reported no detection.

    Astrophysicists highly anticipated the launch of the Hitomi satellite, which carried an instrument—the soft X-ray spectrometer (SXS)—with a spectral resolution 20 times better than the ones aboard previous missions. The SXS would be able to record much sharper signals that would be easier to identify.

    Hitomi recorded the X-ray spectrum of the Perseus galaxy cluster with the protective filter still attached to its soft X-ray spectrometer.
    Hitomi collaboration

    The new data were collected during Hitomi’s first month in space, just before the satellite was lost due to a series of malfunctions. Unfortunately during that time, the SXS was still covered with a protective filter, which absorbed most of the X-ray photons with energies below 5 keV.

    “This limited our ability to take enough data of the 3.5-keV line,” Werner says. “The signal might very well still exist at the much lower flux level observed in the stacked data.”

    Hitomi’s final data at least make it clear that, if the 3.5-keV line exists, its X-ray signal is not anomalously strong. A signal 30 times stronger than expected would have made it through the filter.

    The Hitomi results rule out that the anomalously bright signal in the Perseus cluster was a telltale sign of decaying dark matter particles. But they leave unanswered the question of what exactly scientists detected in the past.

    “It’s really unfortunate that we lost Hitomi,” Bulbul says. “We’ll continue our observations with the other X-ray satellites, but it looks like we won’t be able to solve this issue until another mission goes up.”

    Chances are this might happen in a few years. According to a recent report, the Japan Aerospace Exploration Agency and NASA have begun talks about launching a replacement satellite.

    3
    Hitomi recorded the X-ray spectrum of the Perseus galaxy cluster with the protective filter still attached to its soft X-ray spectrometer.
    Hitomi collaboration

    The new data were collected during Hitomi’s first month in space, just before the satellite was lost due to a series of malfunctions. Unfortunately during that time, the SXS was still covered with a protective filter, which absorbed most of the X-ray photons with energies below 5 keV.

    “This limited our ability to take enough data of the 3.5-keV line,” Werner says. “The signal might very well still exist at the much lower flux level observed in the stacked data.”

    Hitomi’s final data at least make it clear that, if the 3.5-keV line exists, its X-ray signal is not anomalously strong. A signal 30 times stronger than expected would have made it through the filter.

    The Hitomi results rule out that the anomalously bright signal in the Perseus cluster was a telltale sign of decaying dark matter particles. But they leave unanswered the question of what exactly scientists detected in the past.

    “It’s really unfortunate that we lost Hitomi,” Bulbul says. “We’ll continue our observations with the other X-ray satellites, but it looks like we won’t be able to solve this issue until another mission goes up.”

    Chances are this might happen in a few years. According to a recent report, the Japan Aerospace Exploration Agency and NASA have begun talks about launching a replacement satellite.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:23 am on August 3, 2016 Permalink | Reply
    Tags: , Dark Matter, , ,   

    From SLAC: “Physicist Trio Amplifies SLAC Research on Mysterious Forms of Matter” 


    SLAC Lab

    August 2, 2016

    1
    Left: This image shows the remnant of Supernova 1987A, a star explosion detected in 1987, in three different wavelengths (radio, red; visible, green; X-ray, blue). Neutrinos released by supernovae and detected on Earth help researchers understand how stars die. Right: This artist’s impression shows the Milky Way galaxy inside a halo of dark matter (blue), an invisible substance that makes up 85 percent of all matter in the universe. Researchers search for unknown particles and forces related to dark matter. (ALMA/A. Angelich/NASA/ESA, ESO/L. Calçada)

    Elusive Neutrinos and Hypothetical ‘Dark Sector’ Particles Could Hold Answers to Cosmic Mysteries

    All material things appear to be made of elementary particles that are held together by fundamental forces. But what are their exact properties? How do they affect how our universe looks and changes? And are there particles and forces that we don’t know of yet?

    Questions with cosmic implications like these drive many of the scientific efforts at the Department of Energy’s SLAC National Accelerator Laboratory. Three distinguished particle physicists have joined the lab over the past months to pursue research on two particularly mysterious forms of matter: neutrinos and dark matter.

    Neutrinos, which are abundantly produced in nuclear reactions, are among the most common types of particles in the universe. Although they were discovered 60 years ago, their basic properties puzzle scientists to this date.

    Alexander Friedland, a senior staff scientist in SLAC’s Elementary Particle Physics Theory Group, works on techniques that pave the way for future analyses of neutrino bursts from supernovae. Studying the details of these powerful star explosions helps scientists understand how dying stars spit out chemical elements into deep space.

    Natalia Toro and Philip Schuster, associate professors of particle physics and astrophysics at SLAC, look for something even more enigmatic. They develop ideas for experiments that search for hidden particles and forces linked to dark matter, an invisible form of matter that is five times more prevalent than ordinary matter.

    “Alex, Natalia and Philip are significant additions to the SLAC family, whose outstanding expertise tremendously strengthens our research in areas of national priority,” says JoAnne Hewett, head of the lab’s Elementary Particle Physics Division. Neutrino physics and dark matter research are among the five science drivers for U.S. particle physics identified in 2014 by the Particle Physics Project Prioritization Panel. Neutrino research also ranked high in the 2015 long-range plan for nuclear science issued by the Nuclear Science Advisory Committee.

    Neutrinos from Across the Country and from Across the Galaxy

    One of the major neutrino projects with SLAC involvement is the international Deep Underground Neutrino Experiment (DUNE) at the planned Long-Baseline Neutrino Facility (LBNF) – the world’s flagship neutrino experiment for the coming decade and beyond.

    FNAL LBNF/DUNE from FNAL to SURF
    FNAL LBNF/DUNE from FNAL to SURF

    Researchers will send a neutrino beam produced at Fermi National Accelerator Laboratory in Illinois to the Sanford Underground Facility in South Dakota.

    SURF logo

    After travelling 800 miles through the Earth, some of these neutrinos will be detected by the DUNE Far Detector, which will eventually consist of four 10,000-ton modules of liquid argon located 4,850 feet underground.

    FNAL DUNE Argon tank at SURF
    FNAL DUNE Argon tank at SURF

    The ultrasensitive neutrino “eye” will measure how the three known types of neutrinos, called flavors, and their antiparticles morph from one into another during their underground journey. This study will provide crucial insights into the relative masses of neutrino flavors and the possibility that antineutrinos behave differently than neutrinos, which could potentially help explain why the universe is made of matter rather than antimatter. The experiment will also follow up on hints that there may be more than three neutrino flavors in nature.

    “To help DUNE reach its full potential, my work addresses a number of fundamental questions,” says Friedland, SLAC’s first neutrino theorist, who joined the lab in the summer of 2015. “How can additional neutrinos be incorporated into our theories? Are there also additional forces? Is there a link between neutrinos and dark matter? How do neutrinos interact with atomic nuclei in the detector material?”

    In addition to neutrinos from Fermilab, DUNE will also be able to detect very brief neutrino bursts from supernovae – powerful explosions of massive stars with cores that can no longer resist gravity and collapse to form dense neutron stars.

    “Such a burst should be an exquisite probe of neutrino properties,” Friedland says. “Our goal is to understand how to read the signal and optimize our detector for it.”

    Supernova explosions are important events in the universe. They inject chemical elements, synthesized inside stars over their lifetimes, into space, including crucial elements of life. Friedland hopes that DUNE’s data will reveal never-before-seen details in the related neutrino bursts that could open a window into the processes inside dying stars.

    “Our calculations show that those neutrino signals have a certain time structure that is linked to what’s going on in the star,” he says. “Measuring these minute details could help us understand the different stages of a supernova, from the collapse of the star’s core to the outward propagation of powerful shock waves.”

    Such detailed analysis can only be done by looking at neutrinos. Unlike other particles, which frequently interact with their surroundings on their way out of the star and therefore carry the imprint of this complicated environment, neutrinos stream out nearly undisturbed and deliver direct information about the processes in which they were set free.

    “Supernovae go off without warning, and detectable ones don’t occur very often,” says Friedland, who co-leads the DUNE supernova working group. “Although the next supernova neutrino burst may be a decade or more away, what will be seen then is affected by crucial decisions about the detector design made now. My job is to make sure that we’ll be prepared.”

    SLAC provides a unique environment for the pursuit of this line of research, according to Friedland. “The lab is building a strong neutrino program, with experimentalists and theorists working closely together,” he says. “It also unites a number of disciplines under one roof that stimulate and complement each other, from particle physics to astrophysics to computing.”

    Before coming to SLAC, Friedland was at Los Alamos National Laboratory, first as a Richard P. Feynman Fellow and then as a staff scientist. He received his doctorate in physics from the University of California, Berkeley in 2000 and pursued postdoctoral research at the Institute for Advanced Study in Princeton, New Jersey from 2000 to 2002. In addition to neutrinos, Friedland’s studies look into unknown ultraweak forces in nature, extra dimensions beyond space and time and the effect of postulated particles on the evolution of stars.

    Searching for ‘Light Dark Matter’

    Another burning question researchers around the world are yearning to answer is: What is dark matter? With 85 percent of all matter in the universe being dark, this invisible substance has tremendous influence on how the cosmos evolves. Although scientists know that dark matter exists because it gravitationally pulls on ordinary matter, they have yet to find out what it is made of.

    At SLAC, Natalia Toro and Philip Schuster search for entire dark sectors of hypothetical particles and forces that could be linked to dark matter.

    “We work on a number of small-scale experiments that have a real shot at discovering what dark matter is or what it isn’t,” Schuster says. “Unlike most dark matter searches, which focus on rather massive particles, we look for much lighter ones, in a mass range that is surprisingly unexplored.”

    The researchers participate in two experiments that hunt for light dark matter at the Thomas Jefferson National Accelerator Facility in Virginia: the Heavy Photon Search (HPS), for which the scientists developed the theoretical framework, and the A Prime Experiment (APEX), which they co-lead. Both experiments hope to catch a glimpse of dark photons – hypothetical carriers of a new force – that could potentially be produced when powerful electron beams slam into a target. Toro and Schuster are also members of a collaboration that proposed a third experiment at Jefferson Lab to search for dark matter, the Beam Dump Experiment (BDX).

    Similar searches could also be done at SLAC once the upgrade to the lab’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science User Facility, is complete.

    SLAC LCLS-II line
    SLAC LCLS-II

    The future LCLS-II will produce X-rays from a rapid sequence of electron bunches – up to a million per second – that will fly through the facility’s linear particle accelerator.

    “We’re developing ideas for an experiment that would use the dark current of LCLS-II’s electron beam,” Toro says. “This is a small number of unused electrons in between the main bunches that we could extract and shoot into targets for light dark matter searches.”

    A proposal based on this concept is the Light Dark Matter Experiment (LDMX), whose young collaboration is led by researchers from the University of California, Santa Barbara, the University of Minnesota and SLAC.

    At the moment, the parasitic use of LCLS-II is only an idea, but Toro and Schuster have already teamed up with members of SLAC’s Accelerator Directorate to think about how these experiments could be designed and, most importantly, operated without interfering with X-ray laser operations. Together they are exploring the possibility for a future facility for Dark Sector Experiments at LCLS-II (DASEL).

    “The lab has a unique culture of vibrant collaborations,” Toro says. “It creates an ideal environment to follow through with our projects from beginning to end. Here we can establish the theoretical foundation, work on the engineering aspects and turn them into successful experiments, all in one place.”

    See the full article here .

    Please help promote STEM in your local schools.

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    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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