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  • richardmitnick 12:03 pm on November 9, 2017 Permalink | Reply
    Tags: , , Cosmologists have come to realize that our universe may be only one component of the multiverse, Dark Matter, Fred Adams, Mordehai Milgrom and MOND theory, , , , The forces are not nearly as finely tuned as many scientists think, The parameters of our universe could have varied by large factors and still allowed for working stars and potentially habitable planets, The strong interaction- the weak interaction- electromagnetism- gravity   

    From Nautilus: “The Not-So-Fine Tuning of the Universe” 

    Nautilus

    Nautilus

    January 19, 2017 [Just found this referenced in another article.]
    Fred Adams
    Illustrations by Jackie Ferrentino

    Before there is life, there must be structure. Our universe synthesized atomic nuclei early in its history. Those nuclei ensnared electrons to form atoms. Those atoms agglomerated into galaxies, stars, and planets. At last, living things had places to call home. We take it for granted that the laws of physics allow for the formation of such structures, but that needn’t have been the case.

    Over the past several decades, many scientists have argued that, had the laws of physics been even slightly different, the cosmos would have been devoid of complex structures. In parallel, cosmologists have come to realize that our universe may be only one component of the multiverse, a vast collection of universes that makes up a much larger region of spacetime. The existence of other universes provides an appealing explanation for the apparent fine-tuning of the laws of physics. These laws vary from universe to universe, and we live in a universe that allows for observers because we couldn’t live anywhere else.

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    Setting The Parameters: The universe would have been habitable even if the forces of electromagnetism and gravity had been stronger or weaker. The crosshatched area shows the range of values consistent with life. The asterisk shows the actual values in our universe; the axes are scaled to these values. The constraints are that stars must be able to undergo nuclear fusion (below black curve), live long enough for complex life to evolve (below red curve), be hot enough to support biospheres (left of blue curve), and not outgrow their host galaxies (right of the cyan curve). Fred C. Adams.

    Astrophysicists have discussed fine-tuning so much that many people take it as a given that our universe is preternaturally fit for complex structures. Even skeptics of the multiverse accept fine-tuning; they simply think it must have some other explanation. But in fact the fine-tuning has never been rigorously demonstrated. We do not really know what laws of physics are necessary for the development of astrophysical structures, which are in turn necessary for the development of life. Recent work on stellar evolution, nuclear astrophysics, and structure formation suggest that the case for fine-tuning is less compelling than previously thought. A wide variety of possible universes could support life. Our universe is not as special as it might seem.

    The first type of fine-tuning involves the strengths of the fundamental forces of nature in working stars. If the electromagnetic force had been too strong, the electrical repulsion of protons would shut down nuclear fusion in stellar cores, and stars would fail to shine. If electromagnetism had been too weak, nuclear reactions would run out of control, and stars would blow up in spectacular explosions. If gravity had been too strong, stars would either collapse into black holes or never ignite.

    On closer examination, though, stars are remarkably robust. The strength of the electric force could vary by a factor of nearly 100 in either direction before stellar operations would be compromised. The force of gravity would have to be 100,000 times stronger. Going in the other direction, gravity could be a billion times weaker and still allow for working stars. The allowed strengths for the gravitational and electromagnetic forces depend on the nuclear reaction rate, which in turn depends on the strengths of the nuclear forces. If the reaction rate were faster, stars could function over an even wider range of strengths for gravitation and electromagnetism. Slower nuclear reactions would narrow the range.

    In addition to these minimal operational requirements, stars must meet a number of other constraints that further restrict the allowed strength of the forces. They must be hot. The surface temperature of a star must be high enough to drive the chemical reactions necessary for life. In our universe, there are ample regions around most stars where planets are warm enough, about 300 kelvins, to support biology. In universes where the electromagnetic force is stronger, stars are cooler, making them less hospitable.

    Stars must also have long lives. The evolution of complex life forms takes place over enormous spans of time. Since life is driven by a complex ensemble of chemical reactions, the basic clock for biological evolution is set by the time scales of atoms. In other universes, these atomic clocks will tick at different rates, depending on the strength of electromagnetism, and this variation must be taken into account. When the force is weaker, stars burn their nuclear fuel faster, and their lifetimes decrease.

    3
    Mordehai Milgrom
    Also in Physics
    The Physicist Who Denies Dark Matter
    By Oded Carmeli
    He is one of those dark matter people,” Mordehai Milgrom said about a colleague stopping by his office at the Weizmann Institute of Science. Milgrom introduced us, telling me that his friend is searching for evidence of dark matter in READ MORE

    Finally, stars must be able to form in the first place. In order for galaxies and, later, stars to condense out of primordial gas, the gas must be able to lose energy and cool down. The cooling rate depends (yet again) on the strength of electromagnetism. If this force is too weak, gas cannot cool down fast enough and would remain diffuse instead of condensing into galaxies. Stars must also be smaller than their host galaxies—otherwise star formation would be problematic. These effects put another lower limit on the strength of electromagnetism.

    Putting it all together, the strengths of the fundamental forces can vary by several orders of magnitude and still allow planets and stars to satisfy all the constraints (as illustrated in the figure below). The forces are not nearly as finely tuned as many scientists think.

    A second example of possible fine-tuning arises in the context of carbon production. After moderately large stars have fused the hydrogen in their central cores into helium, helium itself becomes the fuel. Through a complicated set of reactions, helium is burned into carbon and oxygen. Because of their important role in nuclear physics, helium nuclei are given a special name: alpha particles. The most common nuclei are composed of one, three, four, and five alpha particles. The nucleus with two alpha particles, beryllium-8, is conspicuously absent, and for a good reason: It is unstable in our universe.

    The instability of beryllium creates a serious bottleneck for the creation of carbon. As stars fuse helium nuclei together to become beryllium, the beryllium nuclei almost immediately decay back into their constituent parts. At any given time, the stellar core maintains a small but transient population of beryllium. These rare beryllium nuclei can interact with helium to produce carbon. Because the process ultimately involves three helium nuclei, it is called the triple-alpha reaction. But the reaction is too slow to produce the amount of carbon observed in our universe.

    To resolve this discrepancy, physicist Fred Hoyle predicted in 1953 that the carbon nucleus has to have a resonant state at a specific energy, as if it were a little bell that rang with a certain tone. Because of this resonance, the reaction rates for carbon production are much larger than they would be otherwise—large enough to explain the abundance of carbon found in our universe. The resonance was later measured in the laboratory at the predicted energy level.

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    Credit above

    The worry is that, in other universes, with alternate strengths of the forces, the energy of this resonance could be different, and stars would not produce enough carbon. Carbon production is compromised if the energy level is changed by more than about 4 percent. This issue is sometimes called the triple-alpha fine-tuning problem.

    Fortunately, this problem has a simple solution. What nuclear physics takes away, it also gives. Suppose nuclear physics did change by enough to neutralize the carbon resonance. Among the possible changes of this magnitude, about half would have the side effect of making beryllium stable, so the loss of the resonance would become irrelevant. In such alternate universes, carbon would be produced in the more logical manner of adding together alpha particles one at a time. Helium could fuse into beryllium, which could then react with additional alpha particles to make carbon. There is no fine-tuning problem after all.

    A third instance of potential fine-tuning concerns the simplest nuclei composed of two particles: deuterium nuclei, which contain one proton and one neutron; diprotons, consisting of two protons; and dineutrons, consisting of two neutrons. In our universe, only deuterium is stable. The production of helium takes place by first combining two protons into deuterium.

    If the strong nuclear force had been even stronger, diprotons could have been stable. In this case, stars could have generated energy through the simplest and fastest of nuclear reactions, where protons combine to become diprotons and eventually other helium isotopes. It is sometimes claimed that stars would then burn through their nuclear fuel at catastrophic rates, resulting in lifetimes that are too short to support biospheres. Conversely, if the strong force had been weaker, then deuterium would be unstable, and the usual stepping stone on the pathway to heavy elements would not be available. Many scientists have speculated that the absence of stable deuterium would lead to a universe with no heavy elements at all and that such a universe would be devoid of complexity and life.

    As it turns out, stars are remarkably stable entities. Their structure adjusts automatically to burn nuclear fuel at exactly the right rate required to support themselves against the crush of their own gravity. If the nuclear reaction rates are higher, stars will burn their nuclear fuel at a lower central temperature, but otherwise they will not be so different. In fact, our universe has an example of this type of behavior. Deuterium nuclei can combine with protons to form helium nuclei through the action of the strong force. The cross section for this reaction, which quantifies the probability of its occurrence, is quadrillions of times larger than for ordinary hydrogen fusion. Nonetheless, stars in our universe burn their deuterium in a relatively uneventful manner. The stellar core has an operating temperature of 1 million kelvins, compared to the 15 million kelvins required to burn hydrogen under ordinary conditions. These deuterium-burning stars have cooler centers and are somewhat larger than the sun, but are otherwise unremarkable.

    Similarly, if the strong nuclear force were lower, stars could continue to operate in the absence of stable deuterium. A number of different processes provide paths by which stars can generate energy and synthesize heavy elements. During the first part of their lives, stars slowly contract, their central cores grow hotter and denser, and they glow with the power output of the sun. Stars in our universe eventually become hot and dense enough to ignite nuclear fusion, but in alternative universes they could continue this contraction phase and generate power by losing gravitational potential energy. The longest-lived stars could shine with a power output roughly comparable to the sun for up to 1 billion years, perhaps long enough for biological evolution to take place.

    For sufficiently massive stars, the contraction would accelerate and become a catastrophic collapse. These stellar bodies would basically go supernova. Their central temperatures and densities would increase to such large values that nuclear reactions would ignite. Many types of nuclear reactions would take place in the death throes of these stars. This process of explosive nucleosynthesis could supply the universe with heavy nuclei, in spite of the lack of deuterium.

    Once such a universe produces trace amounts of heavy elements, later generations of stars have yet another option for nuclear burning. This process, called the carbon-nitrogen-oxygen cycle, does not require deuterium as an intermediate state. Instead, carbon acts as a catalyst to instigate the production of helium. This cycle operates in the interior of the sun and provides a small fraction of its total power. In the absence of stable deuterium, the carbon-nitrogen-oxygen cycle would dominate the energy generation. And this does not exhaust the options for nuclear power generation. Stars could also produce helium through a triple-nucleon process that is roughly analogous to the triple-alpha process for carbon production. Stars thus have many channels for providing both energy and complex nuclei in alternate universes.

    A fourth example of fine-tuning concerns the formation of galaxies and other large-scale structures. They were seeded by small density fluctuations produced in the earliest moments of cosmic time. After the universe had cooled down enough, these fluctuations started to grow stronger under the force of gravity, and denser regions eventually become galaxies and galaxy clusters. The fluctuations started with a small amplitude, denoted Q, equal to 0.00001. The primeval universe was thus incredibly smooth: The density, temperature, and pressure of the densest regions and of the most rarefied regions were the same to within a few parts per 100,000. The value of Q represents another possible instance of fine-tuning in the universe.

    If Q had been lower, it would have taken longer for fluctuations to grow strong enough to become cosmic structures, and galaxies would have had lower densities. If the density of a galaxy is too low, the gas in the galaxy is unable to cool. It might not ever condense into galactic disks or coalesce into stars. Low-density galaxies are not viable habitats for life. Worse, a long enough delay might have prevented galaxies from forming at all. Beginning about 4 billion years ago, the expansion of the universe began to accelerate and pull matter apart faster than it could agglomerate—a change of pace that is usually attributed to a mysterious dark energy. If Q had been too small, it could have taken so long for galaxies to collapse that the acceleration would have started before structure formation was complete, and further growth would have been suppressed. The universe could have ended up devoid of complexity, and lifeless. In order to avoid this fate, the value of Q cannot be smaller by more than a factor of 10.

    What if Q had been larger? Galaxies would have formed earlier and ended up denser. That, too, would have posed a danger for the prospects of habitability. Stars would have been much closer to one another and interacted more often. In so doing, they could have stripped planets out of their orbits and sent them hurtling into deep space. Furthermore, because stars would be closer together, the night sky would be brighter—perhaps as bright as day. If the stellar background were too dense, the combined starlight could boil the oceans of any otherwise suitable planets.

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    Galactic What-If: A galaxy that formed in a hypothetical universe with large initial density fluctuations might be even more hospitable than our Milky Way. The central region is too bright and hot for life, and planetary orbits are unstable. But the outer region is similar to the solar neighborhood. In between, the background starlight from the galaxy is comparable in brightness to the sunlight received by Earth, so all planets, no matter their orbits, are potentially habitable. Fred C. Adams.

    In this case, the fine-tuning argument is not very constraining. The central regions of galaxies could indeed produce such intense background radiation that all planets would be rendered uninhabitable. But the outskirts of galaxies would always have a low enough density for habitable planets to survive. An appreciable fraction of galactic real estate remains viable even when Q is thousands of times larger than in our universe. In some cases, a galaxy might be even more hospitable. Throughout much of the galaxy, the night sky could have the same brightness as the sunshine we see during the day on Earth. Planets would receive their life-giving energy from the entire ensemble of background stars rather than from just their own sun. They could reside in almost any orbit. In an alternate universe with larger density fluctuations than our own, even Pluto would get as much daylight as Miami. As a result, a moderately dense galaxy could have more habitable planets than the Milky Way.

    In short, the parameters of our universe could have varied by large factors and still allowed for working stars and potentially habitable planets. The force of gravity could have been 1,000 times stronger or 1 billion times weaker, and stars would still function as long-lived nuclear burning engines. The electromagnetic force could have been stronger or weaker by factors of 100. Nuclear reaction rates could have varied over many orders of magnitude. Alternative stellar physics could have produced the heavy elements that make up the basic raw material for planets and people. Clearly, the parameters that determine stellar structure and evolution are not overly fine-tuned.

    Given that our universe does not seem to be particularly fine-tuned, can we still say that our universe is the best one for life to develop? Our current understanding suggests that the answer is no. One can readily envision a universe that is friendlier to life and perhaps more logical. A universe with stronger initial density fluctuations would make denser galaxies, which could support more habitable planets than our own. A universe with stable beryllium would have straightforward channels available for carbon production and would not need the complication of the triple-alpha process. Although these issues are still being explored, we can already say that universes have many pathways for the development of complexity and biology, and some could be even more favorable for life than our own. In light of these generalizations, astrophysicists need to reexamine the possible implications of the multiverse, including the degree of fine-tuning in our universe.

    See the full article here .

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    • stewarthoughblog 1:13 am on November 10, 2017 Permalink | Reply

      The proposition that long-lived stars could last 1by and possibly be sufficient for life to evolve is not consistent with what science has observed with our solar system, planet and the origin of life. It is estimated that the first life did not appear until almost 1by after formation, making this wide speculation.

      The idea that an increased density of stars in the galaxy could support increased habitability of planets is inconsistent with astrophysical understanding of the criticality of solar radiation to not destroy all life and all biochemicals required.

      It is also widely speculative to propose that any of the fundamental constants and force tolerances can be virtually arbitrarily reassigned with minimal affect without much more serious scientific analysis. In light of the fundamental fact that the understanding of the origin of life naturalistically is a chaotic mess, it is widely speculative to conjecture the fine-tuning of the universe is not critical.

      Like

    • richardmitnick 10:13 am on November 10, 2017 Permalink | Reply

      Thanks for reading and commenting. I appreciate it.

      Like

  • richardmitnick 3:37 pm on November 1, 2017 Permalink | Reply
    Tags: , , , , Dark Matter, Milky Way Dark Matter Halo, ,   

    From phys.org: “One step closer to defining dark matter, GPS satellite atomic clocks on the hunt” 

    physdotorg
    phys.org

    November 1, 2017

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    Physics professors Andrei Derevianko, left, and Geoff Blewitt of the University of Nevada, Reno College of Science, explain their research to discover how to detect dark matter, and ultimately to define more accurately what kind of particle it is. Credit: Mike Wolterbeek, University of Nevada, Reno

    One professor who studies the earth and one who studies space came together in the pursuit to detect and define dark matter. They are one step closer. Using 16 years of archival data from GPS satellites that that orbit the earth, the University of Nevada, Reno team, Andrei Derevianko and Geoff Blewitt in the College of Science, looked for dark matter clumps in the shape of walls or bubbles and which would extend far out beyond the GPS orbits, the solar system and beyond.

    A scientific article of the team’s work was just published in the journal Nature Communications and just in time for Dark Matter Day, Oct. 31. Dark matter makes up 85 percent of all matter in the universe. While there are multiple astrophysical evidences for dark matter, its nature remains a great mystery. Many forms for dark matter have been hypothesized, theirs is that this form of dark matter, arising from ultralight quantum fields, would form macroscopic objects.

    “We are another step closer to discovering how to detect dark matter, and ultimately to define more accurately what it is, what kind of particle it is” Derevianko said. “Mining these archival data, we found no evidence for domain walls of ultralight dark matter at our current sensitivity level. However, this search rules out a vast region of possibilities for this type of dark matter models.”

    The team focused on ultralight fields that might cause variations in the fundamental constants of nature – such as masses of electrons and quarks and electric charges. The variations could lead to shifts in atomic energy levels, which may be measurable by monitoring atomic frequencies. That’s where the GPS satellites come in. Global positioning system navigation relies on precision timing signals furnished by atomic clocks.

    “Geoff has been using the atomic clocks on the GPS satellites in his geodetic work – measuring uplift of tectonic plates, the shape of the earth, earthquakes, global sea levels, so is familiar with the precision of the system,” Derevianko said. “I’ve worked on devising more accurate atomic clocks. We realized the GPS system could be used to detect listen to the dark matter sweeping through us.

    “Instead of spending billions of dollars to eliminate some plausible dark mater models, we repurposed these common tools (GPS atomic clocks) we use every day to do basic, fundamental science to look for the answers to this great mystery – to devise our own planet-sized dark matter detector.”

    Speeding through the galaxy

    The Earth is speeding through the Milky Way dark matter halo at 300 kilometers per second or one-one thousandth the speed of light. And dark matter clumps are estimated to take 3 minutes to cross the GPS constellation.

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    Milky Way Dark Matter Halo – CERN

    “It’s like a wall moving through a network of clocks causing a wave of atomic clock glitches propagating through the GPS system at galactic speeds,” Derevianko, a professor of quantum physics, said. “The idea is that when the clump overlaps with us, it pulls on the particle masses and forces acting between the particles. Mind you this pull is really weak, otherwise we would have noticed it. However, ultra-sensitive devices like atomic clocks could be sensitive to such pulls.”

    They looked for the predicted patterns of clock glitches, as the earth, and the satellites, moved through the halo of dark matter in the galaxy. The data came from the 32 satellites in the 31,000-mile-wide GPS network and ground-based GPS equipment, every 30-seconds for 16 years. The team used data from sources around the world and in particular from the Jet Propulsion Laboratory.

    “What we looked for was clumps of dark matter in the shape of walls, using a model that – if it exists – would have collisions that are evidenced in irregularities in the atomic clock signals,” Benjamin Roberts, post-doctoral associate and lead author for the Nature paper, said. “While there is no definitive evidence after looking at 16 years of data, it could be that the interaction is weaker or that the defects cross paths with the Earth less often. Some markers indicate it could possibly be a smaller defect.”

    See the full article here .

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  • richardmitnick 7:14 am on November 1, 2017 Permalink | Reply
    Tags: , Dark Matter, Interactions Collaboration, , ,   

    From The New Yorker: “Dark Matter Gets Its Day” 

    new-yorker-bloc-rea-irvin
    Rea Irvin

    The New Yorker

    10.31.17
    Siobhan Roberts

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    A new cosmological celebration, coinciding with Halloween, seeks to shed light on one of the great mysteries of the universe: dark matter. Photograph by Irina Dmitrienko / Alamy.

    Not long ago, the actor Tilda Swinton—cosmic muse to cinéastes, fashion designers, and physicists—took on another shape-shifting role as the voice of a new a planetarium film, Phantom of the Universe: The Hunt for Dark Matter. “As we look out into the night sky, we are both dazzled and comforted by the patches of light we find there,” her narration begins. In time, Swinton continues, astronomers started to suspect that there was something more out there than these brilliant moons, stars, and galaxies—“something hiding in the dark spaces.” The film premièred in Mexico City, on Sunday, and today has special showings worldwide in celebration of this, the inaugural Dark Matter Day.

    Everything that humans have seen up until now exists in the 4.9 per cent of the universe that interacts with light. The rest is hidden from view. Most of it, physicists believe—68.3 per cent—is dark energy, an enigmatic force that drives the accelerating expansion of the cosmos. The rest—26.8 per cent—consists of dark matter, a ghostly goo that is thought to hold the cosmos together. This is why the Interactions Collaboration, a global consortium of particle-physics laboratories, has reimagined Halloween as Dark Matter Day. “Dark matter seems to ‘hide’ in plain sight and doesn’t play by the known rules of physics,” a promotional F.A.Q. explains. “It’s like a costumed trick-or-treater who rings the doorbell and then dashes away, and scientists are trying to unmask it!”

    Dark matter was first theorized, in the nineteen-thirties, by Caltech’s Fritz Zwicky, who reputedly referred to his colleagues at the Mount Wilson Observatory, in Los Angeles, as “spherical bastards,” since he found them equally disagreeable from all sides.

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    Fritz Zwicky

    Forty years later, Vera Rubin, of the Carnegie Institution for Science, in Washington, D.C., confirmed Zwicky’s theory.

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    Vera Rubin

    Studying the rotation of galaxies, Rubin and her collaborators observed that, given the galaxies’ spiralling speeds, and given their visible mass, these stable structures should in fact be flying apart. This amounted to circumstantial evidence that an invisible incarnation of matter—a halo, as it’s occasionally called—kept them whole.

    Now thousands of physicists have joined the hunt. But looking for the subatomic source of dark matter—the leading candidate is known as the WIMP, for weakly interacting massive particle—has proved an expensive and frustrating, if occasionally edifying, odyssey. At the European Organization for Nuclear Research (CERN), in Switzerland, where Dark Matter Day will be celebrated with Dark Matter Cake—baked with the cosmically correct proportions of white-chocolate chips (visible matter), dark-chocolate chips (dark matter), and beetroot (dark energy)—the universe’s mystery ingredient is “definitely in the spotlight now,” Oliver Buchmueller, a senior physicist at Imperial College London, told me. Now that the Higgs boson is well accounted for, dark matter has become one of the Large Hadron Collider’s main targets. The favored model for predicting dark matter has long been supersymmetry. As Swinton explains in the film, “According to this theory, for every known particle, like an electron or quark, there’s a corresponding superparticle with a much greater mass.” But since none of these partners have shown themselves at the L.H.C., researchers are now testing more generic scenarios. “One hypothesis is that the Higgs could be a portal connecting us to the dark world,” Buchmueller said. “We know that the Higgs boson gives mass to all our fundamental particles. But, instead of just decaying to these particles we know in the visible world, the Higgs might also decay to the dark-matter particles.” So far, though, no dice.

    SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario


    SNOLAB, a Canadian underground physics laboratory at a depth of 2 km in Vale’s Creighton nickel mine in Sudbury, Ontario

    Here the goal is to actually observe dark-matter particles as they pass through the planet; the overlying rock filters out the noisy cosmic rays that would otherwise smother the signal. On a visit in August of last year, I joined a group of miners aboard the 8:05 A.M. cage, travelling downward at twenty-five miles per hour. (Thankfully, I didn’t faint; enough SNOLAB visitors do that the miners call them SNOflakes.) I was there to see the DEAP-3600 liquid-argon detector, which, after six years in the making, was just about to become operational.

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    The ultra-pure argon, cooled to minus 297 degrees Fahrenheit, is meant to serve as a conduit of sorts, lighting up in the presence of dark matter. Almost a year later, in July, 2017, the DEAP team published its first results: “No candidate particles are observed.” As Richard Gaitskell, the spokesman for the equally unsuccessful Large Underground Xenon detector, in the Black Hills of South Dakota, told me, “So far we’ve always gotten a negative result. Which means we only know what dark matter isn’t.” The upshot, he said, is that “there are basically thousands of models of particle physics lying bloodied in the gutter.”

    Along the way, however, there have been consolation prizes. In September, 2009, M.I.T.’s Tracy Slatyer and her colleagues analyzed new data from the Fermi Gamma-Ray Space Telescope and spotted a fuzzy blob of gamma rays extending far above and below the core of the Milky Way galaxy.

    NASA/Fermi Telescope

    Could this be a relic of dark matter, they wondered? Alas, it turned out to be something else—“Just something we hadn’t dreamed of yet,” Slatyer said: a figure-eight-shaped pair of bubbles, likely an eruption from a black hole five million times as massive as our sun.

    In examining these so-called Fermi bubbles, Slatyer and another team noticed something more: an excess of gamma rays emanating from the galactic center. “We believe that dark matter piles up in the center of galaxies, because it’s pulled there by gravity,” she told me. That makes the galactic center a good place to look, though also a frightening place, she noted, because it’s populated by so many violent and high-energy astrophysical phenomena. The gamma-ray excess could come from dark matter, or it could come from a population of rare millisecond pulsars—city-sized neutron stars spinning around at a rate of a thousand times per second. Slatyer is ninety-five per cent confident that this is another false alarm. (Her more optimistic colleague gives dark matter a fifty-fifty chance.) But, Slatyer said, “the best thing about these false alarms in astrophysical data is that even if they turn out not to be dark matter, they often tell you about something very interesting. You get a discovery either way.”

    Perhaps the most pessimistic proposition involves the recent revival of a radical theory from the nineteen-eighties known as , or modified Newtonian dynamics, which hypothesizes that there is no dark matter—none at all.

    Diamond Light Source, located at the Harwell Science and Innovation Campus in Oxfordshire U.K.

    Rather, the galactic conundrum is solved by a shift in our understanding of gravity. “When I was a kid, I would wake up one night out of every thirty and think, Oh, my God! It’s probably MOND!” Nima Arkani-Hamed, of the Institute for Advanced Study, in Princeton, told me. “And the other twenty-nine nights, I would be happy that it was probably dark matter. Then I became a scientist, and now it’s once a year that I’ll look up and be, like, Oh, my God. Maybe it’s MOND. But I don’t think it is. It doesn’t smell right to me.”

    But, then again, the worst-case scenario is that, in ten years, or a hundred, this spooky predicament remains a mystery. Sure, the joy is in the hunt—and, as Swinton concludes in her narration, “Ultimately, it’s the big questions that bring humankind together”—but to spend lifetimes searching for something and not finding it would be, well, astronomically frustrating. “The problem is, we have no idea what we are looking for,” Hugh Lippincott, of the Fermi National Accelerator Laboratory, outside Chicago, said. “And there is a not insignificant chance, probably better than fifty per cent, that we are never going to find it. That’s the scary part.”

    Interactions Collaboration
    Interactions collaborators include:

    ARC Centre of Excellence for Particle Physics at the Terascale
    1
    Argonne National Laboratory
    2
    Brookhaven National Laboratory

    Deutsches Elektronen-Synchrotron
    4
    European Organization for Nuclear Research
    5
    Fermi National Accelerator Laboratory

    KEK High Energy Accelerator Research Organization
    6
    CNRS Institut National de Physique Nucléaire et de Physique des Particules

    Institute of High Energy Physics, Chinese Academy of Sciences
    7
    IRFU CEA-Saclay laboratory
    8
    INFN Istituto Nazionale di Fisica Nucleare
    9
    Joint Institute for Nuclear Research, Dubna
    9
    IPMU Kavli Institute for the Physics and Mathematics of the Universe
    10
    Laboratori Nazionali del Gran Sasso – INFN
    Laboratory Nazionali di Frascati – INFN
    Lawrence Berkeley National Laboratory
    11
    Nihhef Nationaal Instituut voor Subatomaire Fysica
    12
    STFC Science and Technology Facilities Council

    SLAC National Accelerator Laboratory
    12
    TRIUMF
    13

    See the full article here .

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  • richardmitnick 11:45 am on October 17, 2017 Permalink | Reply
    Tags: , Dark Matter, LZ- LUX-ZEPLIN experiment, , ,   

    From SURF: “LZ team installs detector in water tank” 

    SURF logo
    Sanford Underground levels

    Sanford Underground Research facility

    October 16, 2017
    Constance Walter

    1
    Sally Shaw, a post-doc with the University of California Santa Barbara, poses next to the sodium iodide detector recently installed inside the water tank. Courtesy photo.

    The huge water tank that for four years housed the Large Underground Xenon (LUX) dark matter detector now stands empty. A small sign over the opening that reads, “Danger! Confined space,” bars physical entry, but a solitary note sung by Michael Gaylor, a science professor from Dakota State University, once jumped that barrier and reverberated for 35.4 seconds.

    Starting this week, the tank will be filled with the sounds of collaboration members installing a small detector that will be used to measure radioactivity in the cavern. It’s all part of the plan to build and install the much larger, second-generation dark matter detector, LUX-ZEPLIN (LZ).

    LBNL Lux Zeplin project at SURF

    “We need to pin down the background event rate to better shield our experiment,” said Sally Shaw, a post doc form from the University of California, Santa Barbara (UCSB).

    The detector, a 5-inch by 5-inch cylinder of sodium iodide, will be placed inside the water tank and surrounded by 8 inches of lead bricks. The crystal will be covered on all sides except one, which will be left bare to measure the gamma rays that are produced when things like thorium, uranium and potassium decay. Over the next two weeks, the team will change the position of the detector five times to determine the directionality of the gamma rays.

    Scott Haselschwardt, a graduate student at UCSB, said this is especially important because there is a rhyolite intrusion that runs below the tank and up the west wall of the cavern.

    “This rock is more radioactive than other types of rock, so it can create more backgrounds,” he said. This wasn’t a problem for LUX, Haselschwardt said, but it was smaller than LZ and, therefore, surrounded by more ultra-pure water.

    But LZ is 10 times larger and still must fit inside the same tank, potentially exposing it to more of the radiation that naturally occurs within the rock cavern. And while this radiation is harmless to humans, it can wreak havoc on highly sensitive experiments like LZ.

    “Because it is so much closer to the edges of the water tank, there was a proposal to put in extra shielding—perhaps a lead ring at the bottom of the tank to shield the experiment,” Shaw said.

    Like its much smaller cousin, LZ hopes to find WIMPs, weakly interacting massive particles. Every component must be tested to ensure it is free of any backgrounds, including more than 500 photomultiplier tubes, the titanium for the cryostat and the liquid scintillator that will surround the xenon container. But if the backgrounds emanating from the walls of the cavern are too high, it won’t matter.

    “The whole point is to see whether the lead needs to be used in the design of the shield,” said Umit Utku, a graduate student at University College in London. “Maybe we will realize we don’t need it.”

    Shaw, who created a design for lead shielding within the tank, said it’s critical to fully understand the backgrounds now.

    “If we do need extra shielding, we must adjust the plans before installation of the experiment begins,” she said.

    See the full article here .

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    About us.
    The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

    The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

    Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

    In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

    In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

    The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
    LUX/Dark matter experiment at SURFLUX/Dark matter experiment at SURF

    In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

    Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

    Fermilab LBNE
    LBNE

     
  • richardmitnick 2:20 pm on October 8, 2017 Permalink | Reply
    Tags: , , , , , Dark Matter, , , Perimeter Institute of Theoretical Physics, , ,   

    From Quanta: Women in STEM: “Mining Black Hole Collisions for New Physics” Asimina Arvanitaki 

    Quanta Magazine
    Quanta Magazine

    July 21, 2016
    Joshua Sokol

    The physicist Asimina Arvanitaki is thinking up ways to search gravitational wave data for evidence of dark matter particles orbiting black holes.

    1
    Asimina Arvanitaki during a July visit to the CERN particle physics laboratory in Geneva, Switzerland.
    Samuel Rubio for Quanta Magazine

    When physicists announced in February that they had detected gravitational waves firsthand, the foundations of physics scarcely rattled.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

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

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    The signal exactly matched the expectations physicists had arrived at after a century of tinkering with Einstein’s theory of general relativity. “There is a question: Can you do fundamental physics with it? Can you do things beyond the standard model with it?” said Savas Dimopoulos, a theoretical physicist at Stanford University. “And most people think the answer to that is no.”

    Asimina Arvanitaki is not one of those people. A theoretical physicist at Ontario’s Perimeter Institute of Theoretical Physics,


    Perimeter Institute in Waterloo, Canada

    Arvanitaki has been dreaming up ways to use black holes to explore nature’s fundamental particles and forces since 2010, when she published a paper with Dimopoulos, her mentor from graduate school, and others. Together, they sketched out a “string axiverse,” a pantheon of as yet undiscovered, weakly interacting particles. Axions such as these have long been a favored candidate to explain dark matter and other mysteries.

    In the intervening years, Arvanitaki and her colleagues have developed the idea through successive papers. But February’s announcement marked a turning point, where it all started to seem possible to test these ideas. Studying gravitational waves from the newfound population of merging black holes would allow physicists to search for those axions, since the axions would bind to black holes in what Arvanitaki describes as a “black hole atom.”

    “When it came up, we were like, ‘Oh my god, we’re going to do it now, we’re going to look for this,’” she said. “It’s a whole different ball game if you actually have data.”

    That’s Arvanitaki’s knack: matching what she calls “well-motivated,” field-hopping theoretical ideas with the precise experiment that could probe them. “By thinking away from what people are used to thinking about, you see that there is low-hanging fruit that lie in the interfaces,” she said. At the end of April, she was named the Stavros Niarchos Foundation’s Aristarchus Chair at the Perimeter Institute, the first woman to hold a research chair there.

    It’s a long way to come for someone raised in the small Grecian village of Koklas, where the graduating class at her high school — at which both of her parents taught — consisted of nine students. Quanta Magazine spoke with Arvanitaki about her plan to use black holes as particle detectors. An edited and condensed version of those discussions follows.

    QUANTA MAGZINE: When did you start to think that black holes might be good places to look for axions?

    ASIMINA ARVANITAKI: When we were writing the axiverse paper, Nemanja Kaloper, a physicist who is very good in general relativity, came and told us, “Hey, did you know there is this effect in general relativity called superradiance?” And we’re like, “No, this cannot be, I don’t think this happens. This cannot happen for a realistic system. You must be wrong.” And then he eventually convinced us that this could be possible, and then we spent like a year figuring out the dynamics.
    What is superradiance, and how does it work?

    An astrophysical black hole can rotate. There is a region around it called the “ergo region” where even light has to rotate. Imagine I take a piece of matter and throw it in a trajectory that goes through the ergo region. Now imagine you have some explosives in the matter, and it breaks apart into pieces. Part of it falls into the black hole and part escapes into infinity. The piece that is coming out has more total energy than the piece that went in the black hole.

    You can perform the same experiment by scattering radiation from a black hole. Take an electromagnetic wave pulse, scatter it from the black hole, and you see that the pulse you got back has a higher amplitude.

    So you can send a pulse of light near a black hole in such a way that it would take some energy and angular momentum from the black hole’s spin?

    This is old news, by the way, this is very old news. In ’72 Press and Teukolsky wrote a Nature paper that suggested the following cute thing. Let’s imagine you performed the same experiment as the light, but now imagine that you have the black hole surrounded by a giant mirror. What will happen in that case is the light will bounce on the mirror many times, the amplitude [of the light] grows exponentially, and the mirror eventually explodes due to radiation pressure. They called it the black hole bomb.

    The property that allows light to do this is that light is made of photons, and photons are bosons — particles that can sit in the same space at the same time with the same wave function. Now imagine that you have another boson that has a mass. It can [orbit] the black hole. The particle’s mass acts like a mirror, because it confines the particle in the vicinity of the black hole.

    In this way, axions might get stuck around a black hole?

    This process requires that the size of the particle is comparable to the black hole size. Turns out that [axion] mass can be anywhere from Hubble scale — with a quantum wavelength as big as the universe — or you could have a particle that’s tiny in size.

    So if they exist, axions can bind to black holes with a similar size and mass. What’s next?

    What happens is the number of particles in this bound orbit starts growing exponentially. At the same time the black hole spins down. If you solve for the wave functions of the bound orbits, what you find is that they look like hydrogen wave functions. Instead of electromagnetism binding your atom, what’s binding it is gravity. There are three quantum numbers you can describe, just the same. You can use the exact terminology that you can use in the hydrogen atom.

    How could we check to see if any of the black holes LIGO finds have axion clouds orbiting around black hole nuclei?

    This is a process that extracts energy and angular momentum from the black hole. If you were to measure spin versus mass of black holes, you should see that in a certain mass range for black holes you see no quickly rotating black holes.

    This is where Advanced LIGO comes in. You saw the event they saw. [Their measurements] allowed them to measure the masses of the merging objects, the mass of the final object, the spin of the final object, and to have some information about the spins of the initial objects.

    If I were to take the spins of the black holes before they merged, they could have been affected by superradiance. Now imagine a graph of black hole spin versus mass. Advanced LIGO could maybe get, if the things that we hear are correct, a thousand events per year. Now you have a thousand data points on this plot. So you may trace out the region that is affected by this particle just by those measurements.

    That would be supercool.

    That’s of course indirect. So the other cool thing is that it turns out there are signatures that have to do with the cloud of particles themselves. And essentially what they do is turn the black hole into a gravitational wave laser.

    Awesome. OK, what does that mean?

    2
    Samuel Rubio for Quanta Magazine

    Yeah, what that means is important. Just like you have transitions of electrons in an excited atom, you can have transitions of particles in the gravitational wave atom. The rate of emission of gravitational waves from these transitions is enhanced by the 1080 particles that you have. It would look like a very monochromatic line. It wouldn’t look like a transient. Imagine something now that emits a signal at a very fixed frequency.

    Where could LIGO expect to see signals like this?

    In Advanced LIGO, you actually see the birth of a black hole. You know when and where a black hole was born with a certain mass and a certain spin. So if you know the particle masses that you’re looking for, you can predict when the black hole will start growing the [axion] cloud around it. It could be that you see a merger in that day, and one or 10 years down the line, they go back to the same position and they see this laser turning on, they see this monochromatic line coming out from the cloud.

    You can also do a blind search. Because you have black holes that are roaming the universe by themselves, and they could still have some leftover cloud around them, you can do a blind search for monochromatic gravitational waves.

    Were you surprised to find out that axions and black holes could combine to produce such a dramatic effect?

    Oh my god yes. What are you talking about? We had panic attacks. You know how many panic attacks we had saying that this effect, no, this cannot be true, this is too good to be true? So yes, it was a surprise.

    The experiments you suggest draw from a lot of different theoretical ideas — like how we could look for high-frequency gravitational waves with tabletop sensors, or test whether dark matter oscillates using atomic clocks. When you’re thinking about making risky bets on physics beyond the standard model, what sorts of theories seem worth the effort?

    What is well motivated? Things that are not: “What if you had this?” People imagine: “What if dark matter was this thing? What if dark matter was the other thing?” For example, supersymmetry makes predictions about what types of dark matter should be there. String theory makes predictions about what types of particles you should have. There is always an underlying reason why these particles are there; it’s not just the endless theoretical possibilities that we have.

    And axions fit that definition?

    This is a particle that was proposed 30 years ago to explain the smallness of the observed electric dipole moment of the neutron. There are several experiments around the world looking for it already, at different wavelengths. So this particle, we’ve been looking for it for 30 years. This can be the dark matter. That particle solves an outstanding problem of the standard model, so that makes it a good particle to look for.

    Now, whether or not the particle is there I cannot answer for nature. Nature will have to answer.

    See the full article here .

    Please help promote STEM in your local schools.

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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 5:40 am on October 4, 2017 Permalink | Reply
    Tags: , , , , , Dark Matter, , ESA e-ASTROGAM, , ,   

    From astrobites: “Future Gamma-ray Telescopes and the Search for Dark Matter” 

    Astrobites bloc

    Astrobites

    Oct 3, 2017
    Nora Shipp

    Title: Resolving Dark Matter Subhalos With Future Sub-GeV Gamma-Ray Telescopes
    Authors: Ti-Lin Chou, Dimitrios Tanoglidis, and Dan Hooper
    First Author’s Institution: Dept. of Physics, University of Chicago, USA

    Status: Submitted to the Journal of Cosmology and Astroparticle Physics (open access)

    We are surrounded by undetected dark matter.

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    In fact, our entire Galaxy is enveloped in a large halo of it, but because dark matter does not emit or reflect light, the halo is completely invisible.

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

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

    Inside this halo, orbiting our galaxy, are hundreds of smaller, equally invisible dark matter halos (Figure 1).

    1
    Figure 1. Galaxies like the Milky Way are surrounded by small dark matter halos (blue blobs). Some of these halos contain no stars, but could still produce gamma-rays from dark matter annihilation! Source: ESO

    The larger ones contain their own dwarf galaxies, but the smallest halos are so tiny that they contain no stars at all. However, if the leading theory of WIMP (Weakly Interacting Massive Particle) dark matter is correct, there is one way that we could actually see these dark matter halos without the help of any stars. If dark matter particles are their own antiparticle, they would annihilate when they come into contact with each other, producing various particles, including highly energetic photons known as gamma-rays.

    Gamma-rays have millions of times more energy than the optical photons that human eyes can see, yet these energetic particles are quite difficult to detect. The current leader in gamma-ray detection is the Fermi Gamma-ray Space Telescope, a satellite that has been orbiting the Earth, searching the sky for gamma-rays, for almost 10 years.

    NASA/Fermi Telescope

    NASA/Fermi LAT

    Since Fermi was first launched, scientists have searched the gamma-ray sky for evidence of dark matter annihilation. What makes this search really tricky is that dark matter is not the only thing that produces gamma-rays. The sky is actually full of gamma-rays coming from all directions, produced by clouds of gas, pulsars, and active galactic nuclei, among many other sources (Figure 2 [not shown in article, replaced here).

    3
    Fermi’s Latest Gamma-ray Census Highlights Cosmic Mysteries

    However, those tiny dark matter halos that don’t contain stars or gas or any kind of non-dark matter should only be producing gamma-rays from dark matter annihilation. The catch is that we have no idea where these dark matter halos are. Scientists, therefore, have searched all across the sky for gamma-rays that might be coming from dark halos, and they just might have found a couple.

    Two sources of gamma-rays fit all the requirements – they are in the right part of the sky, do not emit any other kind of light (as you’d expect from a halo containing only dark matter), and appear to extend wider across the sky than the single point of a far away star. However, it’s impossible to tell whether these sources are really extended like a dark matter halo or whether they are just two star-like points so close to each other that they blur together, appearing to Fermi as a single blob. Today’s paper considers whether a proposed successor to Fermi called e-ASTROGAM (Figure 3) will be able to resolve the mystery of these gamma-ray blobs.

    4
    Figure 3. A model of e-Astrogam, one potential successor to the Fermi Gamma-ray Space Telescope. Source: ESA

    Are they in fact dark matter halos (in which case this would be the first confirmed detection of dark matter annihilation!) or are they simply two points blurred into one?

    e-ASTROGAM would be quite similar to Fermi, but with several important changes. The biggest difference is that it would be able to detect gamma-rays at a slightly lower energy than Fermi, giving us a brand new view of the gamma-ray sky. In the context of today’s paper, however, the most significant difference is the angular resolution. Angular resolution determines how close together two objects can get before they blur together into a single blob. The angular resolution of e-ASTROGAM will be about 4-6 times better than Fermi’s in the energy range of these mysterious gamma-ray sources. According to the authors of today’s paper, this should definitely be enough to tell whether they are single extended objects or two independent points that are just too close together for Fermi to see (Figure 4).

    5
    Figure 4. Simulated images of two point sources as seen by Fermi and e-ASTROGAM. On the left, Fermi is unable to distinguish between the two objects, seeing only a single blob of gamma-rays. On the right, e-ASTROGAM, with its superior angular resolution, can tell that the single blob is actually two individual objects. Source: Figure 3 of the paper.

    In order to see just how well e-ASTROGAM will be able to see these objects, the authors modeled fake observations of dark matter annihilation from an extended halo and from two point sources. They determined for different halo sizes and dark matter particles how well e-ASTROGAM will be able to tell whether an object is one extended source or two points. Figure 5 illustrates the difference e-ASTROGAM will make in confirming the nature of these gamma-ray sources. The green and red lines represent how easily Fermi and e-ASTROGAM can distinguish pairs of sources (x-axis) as a function of source brightness (y-axis). e-ASTROGAM reaches much farther along the x-axis, indicating that it can much more easily resolve two point sources. The precise numbers change for different dark matter halos and particles, but in all cases e-ASTROGAM shows a significant improvement over Fermi.

    6
    Figure 5. This plot illustrates how e-ASTROGAM will be able to help distinguish between extended dark matter halos and two nearby points. The y-axis shows how bright the object in question is, and the x-axis is related to how easily the telescope can distinguish between two nearby points and a single extended object. Even with really bright objects Fermi (green) has a hard time distinguishing between the two scenarios, while e-ASTROGAM (red) can more easily tell the difference. Source: Figure 5 of the paper.

    A future gamma-ray telescope like e-ASTROGAM will be an essential tool in determining whether Fermi has in fact detected dark matter annihilation from dark halos. In addition to determining whether the two potential halos detected by Fermi are actually just pairs of close-together point sources, e-ASTROGAM may be able to detect gamma-rays from even more dark matter halos that are too faint for Fermi to observe on its own. e-ASTROGAM with its superior angular resolution and lower energy range would provide a brand new view of the gamma-ray universe, giving us unexpected insight into known and unknown sources of gamma-rays, and perhaps finally revealing the nature of dark matter.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 8:20 am on October 2, 2017 Permalink | Reply
    Tags: , , , , Dark Matter, , Kyoto University, , , University of Tübingen, University of Texas at Austin, University of Tokyo   

    From Science: “Sloshing, supersonic gas may have built the baby universe’s biggest black holes” 

    AAAS
    Science

    Sep. 28, 2017
    Joshua Sokol

    1
    Supermassive black holes a billion times heavier than the sun are too big to have formed conventionally. NASA Goddard Space Flight Center

    A central mystery surrounds the supermassive black holes that haunt the cores of galaxies: How did they get so big so fast? Now, a new, computer simulation–based study suggests that these giants were formed and fed by massive clouds of gas sloshing around in the aftermath of the big bang.

    “This really is a new pathway,” says Volker Bromm, an astrophysicist at the University of Texas in Austin who was not part of the research team. “But it’s not … the one and only pathway.”

    Astronomers know that, when the universe was just a billion years old, some supermassive black holes were already a billion times heavier than the sun. That’s much too big for them to have been built up through the slow mergers of small black holes formed in the conventional way, from collapsed stars a few dozen times the mass of the sun. Instead, the prevailing idea is that these behemoths had a head start. They could have condensed directly out of seed clouds of hydrogen gas weighing tens of thousands of solar masses, and grown from there by gravitationally swallowing up more gas. But the list of plausible ways for these “direct-collapse” scenarios to happen is short, and each option requires a perfect storm of circumstances.

    For theorists tinkering with computer models, the trouble lies in getting a massive amount of gas to pile up long enough to collapse all at once, into a vortex that feeds a nascent black hole like water down a sink drain. If any parts of the gas cloud cool down or clump up early, they will fragment and coalesce into stars instead. Once formed, radiation from the stars would blow away the rest of the gas cloud.

    2
    Computer models show how supersonic streams of gas coalesce around nuggets of dark matter—forming the seed of a supermassive black hole. Shingo Hirano

    One option, pioneered by Bromm and others, is to bathe a gas cloud in ultraviolet light, perhaps from stars in a next-door galaxy, and keep it warm enough to resist clumping. But having a galaxy close enough to provide that service would be quite the coincidence.

    The new study proposes a different origin. Both the early universe and the current one are composed of familiar matter like hydrogen, plus unseen clumps of dark matter.

    Dark Matter Research

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

    Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LUX Dark matter Experiment at SURF, Lead, SD, USA

    ADMX Axion Dark Matter Experiment, U Uashington

    Today, these two components move in sync. But very early on, normal matter may have sloshed back and forth at supersonic speeds across a skeleton provided by colder, more sluggish dark matter. In the study, published today in Science, simulations show that where these surges were strong, and crossed the path of heavy clumps of dark matter, the gas resisted premature collapse into stars and instead flowed into the seed of a supermassive black hole. These scenarios would be rare, but would still roughly match the number of supermassive black holes seen today, says Shingo Hirano, an astrophysicist at the University of Texas and lead author of the study.

    Priya Natarajan, an astrophysicist at Yale University, says the new simulation represents important computational progress. But because it would have taken place at a very distant, early moment in the history of the universe, it will be difficult to verify. “I think the mechanism itself in detail is not going to be testable,” she says. “We will never see the gas actually sloshing and falling in.”

    But Bromm is more optimistic, especially if such direct-collapse black hole seeds also formed slightly later in the history of the universe. He, Natarajan, and other astronomers have been looking for these kinds baby black holes, hoping to confirm that they do, indeed, exist and then trying to work out their origins from the downstream consequences.

    In 2016, they found several candidates, which seem to have formed through direct collapse and are now accreting matter from clouds of gas. And earlier this year, astronomers showed that the early, distant universe is missing the glow of x-ray light that would be expected from a multitude of small black holes—another sign favoring the sudden birth of big seeds that go on to be supermassive black holes. Bromm is hopeful that upcoming observations will provide more definite evidence, along with opportunities to evaluate the different origin theories. “We have these predictions, we have the signatures, and then we see what we find,” he says. “So the game is on.”

    See the full article here .

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  • richardmitnick 2:00 pm on September 29, 2017 Permalink | Reply
    Tags: , , , , , , Dark Matter,   

    From CfA: “New Insights on Dark Energy” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    Inflationary Universe. NASA/WMAP

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

    The universe is not only expanding – it is accelerating outward, driven by what is commonly referred to as “dark energy.”

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    The term is a poetic analogy to label for dark matter, the mysterious material that dominates the matter in the universe and that really is dark because it does not radiate light (it reveals itself via its gravitational influence on galaxies).

    Dark Matter Research

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

    Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LUX Dark matter Experiment at SURF, Lead, SD, USA

    ADMX Axion Dark Matter Experiment, U Uashington

    Two explanations are commonly advanced to explain dark energy. The first, as Einstein once speculated, is that gravity itself causes objects to repel one another when they are far enough apart (he added this “cosmological constant” term to his equations). The second explanation hypothesizes (based on our current understanding of elementary particle physics) that the vacuum has properties that provide energy to the cosmos for expansion.

    For several decades cosmologies have successfully used a relativistic equation with dark matter and dark energy to explain increasingly precise observations about the cosmic microwave background, the cosmological distribution of galaxies, and other large-scale cosmic features.

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

    But as the observations have improved, some apparent discrepancies have emerged. One of the most notable is the age of the universe: there is an almost 10% difference between measurements inferred from the Planck satellite data and those from so-called Baryon Acoustic Oscillation experiments. The former relies on far-infrared and submillimeter measurements of the cosmic microwave background [CMB] and the latter on spatial distribution of visible galaxies.

    BOSS Supercluster Baryon Oscillation Spectroscopic Survey (BOSS)

    CMB per ESA/Planck

    ESA/Planck

    CfA astronomer Daniel Eisenstein was a member of a large consortium of scientists who suggest that most of the difference between these two methods, which sample different components of the cosmic fabric, could be reconciled if the dark energy were not constant in time. The scientists apply sophisticated statistical techniques to the relevant cosmological datasets and conclude that if the dark energy term varied slightly as the universe expanded (though still subject to other constraints), it could explain the discrepancy. Direct evidence for such a variation would be a dramatic breakthrough, but so far has not been obtained. One of the team’s major new experiments, the Dark Energy Spectroscopic Instrument (DESI) Survey…

    LBNL/DESI Dark Energy Spectroscopic Instrument for the Nicholas U. Mayall 4-meter telescope at Kitt Peak National Observatory near Tucson, Ariz, USA

    …could settle the matter. It will map over twenty-five million galaxies in the universe, reaching back to objects only a few billion years after the big bang, and should be completed sometime in the mid 2020’s.

    Reference(s):

    Dynamical Dark Energy in Light of the Latest Observations, Gong-Bo Zhao et al. Nature Astronomy, 1, 627, 2017

    See the full article here .

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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 3:21 pm on September 28, 2017 Permalink | Reply
    Tags: AMS, Dark Matter, , ,   

    From Quantum Diaries: “Latest news from outer space on dark matter” 

    9.28.17
    Pauline Gagnon

    Pauline Gagnon

    To celebrate the first five years of operation on board the International Space Station, Professor Sam Ting, the spokesperson for the Alpha Magnetic Spectrometer (AMS-02) Collaboration just presented their latest results at a recent seminar held at CERN. With a sample of 90 million events collected in cosmic rays, they now have the most precise data on a wide range of particles found in outer space.

    CERN Alpha Magnetic Spectrometer

    2
    Sam Ting, CERN and MIT

    Many physicists wonder if the AMS Collaboration will resolve the enigma on the origin of the excess of positrons found in cosmic rays. Positrons are the antimatter of electrons. Given that we live in a world made almost uniquely of matter, scientists have been wondering for more than a decade where these positrons come from. It is well known that some positrons are produced when cosmic rays interact with the interstellar material. What is puzzling is that more positrons are observed than what is expected from this source alone.

    Various hypotheses have been formulated to explain the origin of these extra positrons. One particularly exciting possibility is that these positrons could emanate from the annihilation of dark matter particles. Dark matter is some form of invisible matter that is observed in the Universe mostly through its gravitational effects. Regular matter, everything we know on Earth but also everything found in stars and galaxies, emits light when heated up, just like a piece of heated metal glows.

    Dark matter emits no light, hence its name. It is five times more prevalent than regular matter. Although no one knows, we suspect dark matter, just like regular matter, is made of particles but no one has yet been able to capture a particle of dark matter. However, if dark matter particles exist, they could annihilate with each other and produce an electron and a positron, or a proton and antiproton pair. This would at long last establish that dark matter particles exist and reveal some clues on their characteristics.

    An alternative but less exotic explanation would be that the observed excess of positrons comes from pulsars. Pulsars are neutron stars with a strong magnetic field that emit pulsed light. But light is made of photons and photons can also decay into an electron and a positron. So both the pulsar and the dark matter annihilation provide a plausible explanation on the source of these positrons.

    To tell the difference, one must measure the energy of all positrons found in cosmic rays and see how many are found at high energy. This is what AMS has done and their data are shown on the left plot below, where we see the flux of positrons (vertical axis) found at different energies (horizontal axis). The flux combines the number of positrons found with their energy cube. The green curve gives how many positrons are expected from cosmic rays hitting the interstellar material (ISM).

    If the excess of positrons were to come from dark matter annihilation, no positron would be found with an energy exceeding the mass of the dark matter particle. They would have an energy distribution similar to the brown curve on the plot below as expected for dark matter particles having a mass of 1 TeV, a thousand times heavier than a proton. In that case, the positrons energy distribution curve would drop off sharply. The red dots represent the AMS data with their experimental errors shown by the vertical bars. If, on the other end, the positrons came from pulsars, the drop at high energy would be less pronounced.

    2
    source: AMS Collaboration

    The name of the game is therefore to figure out precisely what is happening at high energy. But there are much fewer positrons there, making it very difficult to see what is happening as indicated by the large error bars attached to the data points at higher energy. These indicate the size of the experimental errors.

    But by looking at the fraction of positrons found in all data collected for electrons and positrons (right plot above), some of the experimental errors cancel out. AMS has collected over a million positrons and 16 million electrons. The red dots on the right plot show the fraction of positrons found in their sample as a function of energy. Given the actual precision of these measurements, it is still not completely clear if this fraction is really falling off at higher energy or not.

    The AMS Collaboration hopes however to have enough data to distinguish the two hypotheses by 2024 when the ISS will cease operation. These projections are shown on the next two plots both for the positrons flux (left) and the positron fraction (right). As it stands today, both hypotheses are still possible given the size of the experimental errors.

    3
    source: AMS Collaboration

    There is another way to test the dark matter hypothesis. By interacting with the interstellar material, cosmic rays produce not only positrons, but also antiprotons. And so would dark matter annihilations but pulsars cannot produce antiprotons. If there were also an excess of antiprotons in outer space that could not be accounted for by cosmic rays, it would reinforce the dark matter hypothesis. But this entails knowing precisely how cosmic rays propagate and interact with the interstellar medium.

    Using the AMS large sample of antiprotons, Prof. Sam Ting claimed that such excess already exists. He showed the following plot giving the fraction of antiprotons found in the total sample of protons and antiprotons as a function of their energy. The red dots represent the AMS measurements, the brown band, some theoretical calculation for cosmic rays, and the blue band, what could be coming from dark matter.

    4
    source: AMS Collaboration

    This plot clearly suggests that more antiprotons are found than what is expected from cosmic rays interacting with the interstellar material (ISM). But both Dan Hooper and Ilias Cholis, two theorists and experts on this subject, strongly disagree, saying that the uncertainty on this calculation is much larger. They say that the following plot (from Cuoco et al.) is by far more realistic. The pink dots represent the AMS data for the antiproton fraction. The data seem in good agreement with the theoretical prediction given by the black line and grey bands. So there are no signs of a large excess of antiprotons here. We need to wait for a few more years before the AMS data and the theoretical estimates are precise enough to determine if there is an excess or not.

    5
    source: Cuoco, Krämer and Korsmeier, arXiv:1610.03071v1

    The AMS Collaboration could have another huge surprise is stock: discovering the first antiatoms of helium in outer space. Given that anything more complex than an antiproton is much more difficult to produce, they will need to analyze huge amounts of data and further reduce all their experimental errors before such a discovery could be established.

    Will AMS discover antihelium atoms in cosmic rays, establish the presence of an excess of antiprotons or even solve the positron enigma? AMS has lots of exciting work on its agenda. Well worth waiting for it!

    Pauline Gagnon

    See the full article here .

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  • richardmitnick 8:05 pm on September 25, 2017 Permalink | Reply
    Tags: , , , , , , , , Dark Matter, DM axions, , , , The origin of solar flares,   

    From CERN Courier: “Study links solar activity to exotic dark matter” 


    CERN Courier

    1
    Solar-flare distributions

    The origin of solar flares, powerful bursts of radiation appearing as sudden flashes of light, has puzzled astrophysicists for more than a century. The temperature of the Sun’s corona, measuring several hundred times hotter than its surface, is also a long-standing enigma.

    A new study suggests that the solution to these solar mysteries is linked to a local action of dark matter (DM). If true, it would challenge the traditional picture of DM as being made of weakly interacting massive particles (WIMPs) or axions, and suggest that DM is not uniformly distributed in space, as is traditionally thought.

    The study is not based on new experimental data. Rather, lead author Sergio Bertolucci, a former CERN research director, and collaborators base their conclusions on freely available data recorded over a period of decades by geosynchronous satellites. The paper presents a statistical analysis of the occurrences of around 6500 solar flares in the period 1976–2015 and of the continuous solar emission in the extreme ultraviolet (EUV) in the period 1999–2015. The temporal distribution of these phenomena, finds the team, is correlated with the positions of the Earth and two of its neighbouring planets: Mercury and Venus. Statistically significant (above 5σ) excesses of the number of flares with respect to randomly distributed occurrences are observed when one or more of the three planets find themselves in a slice of the ecliptic plane with heliocentric longitudes of 230°–300°. Similar excesses are observed in the same range of longitudes when the solar irradiance in the EUV region is plotted as a function of the positions of the planets.

    These results suggest that active-Sun phenomena are not randomly distributed, but instead are modulated by the positions of the Earth, Venus and Mercury. One possible explanation, says the team, is the existence of a stream of massive DM particles with a preferred direction, coplanar to the ecliptic plane, that is gravitationally focused by the planets towards the Sun when one or more of the planets enter the stream. Such particles would need to have a wide velocity spectrum centred around 300 km s–1 and interact with ordinary matter much more strongly than typical DM candidates such as WIMPs. The non-relativistic velocities of such DM candidates make planetary gravitational lensing more efficient and can enhance the flux of the particles by up to a factor of 106, according to the team.

    Co-author Konstantin Zioutas, spokesperson for the CAST experiment at CERN, accepts that this interpretation of the solar and planetary data is speculative – particularly regarding the mechanism by which a temporarily increased influx of DM actually triggers solar activity.

    CERN CAST Axion Solar Telescope

    However, he says, the long persisting failure to detect the ubiquitous DM might be due to the widely assumed small cross-section of its constituents with ordinary matter, or to erroneous DM modelling. “Hence, the so-far-adopted direct-detection concepts can lead us towards a dead end, and we might find that we have overlooked a continuous communication between the dark and the visible sector.”

    Models of massive DM streaming particles that interact strongly with normal matter are few and far between, although the authors suggest that “antiquark nuggets” are best suited to explain their results. “In a few words, there is a large ‘hidden’ energy in the form of the nuggets,” says Ariel Zhitnitsky, who first proposed the quark-nugget dark-matter model in 2003. “In my model, this energy can be precisely released in the form of the EUV radiation when the anti-nuggets enter the solar corona and get easily annihilated by the light elements present in such a highly ionised environment.”

    The study calls for further investigation, says researchers. “It seems that the statistical analysis of the paper is accurate and the obtained results are rather intriguing,” says Rita Bernabei, spokesperson of the DAMA experiment, which for the first time in 1998 claimed to have detected dark matter in the form of WIMPs on the basis of an observed seasonal modulation of a signal in their scintillation detector.

    DAMA-LIBRA at Gran Sasso

    “However, the paper appears to be mostly hypothetical in terms of this new type of dark matter.”

    The team now plans to produce a full simulation of planetary lensing taking into account the simultaneous effect of all the planets in the solar system, and to extend the analysis to include sunspots, nano-flares and other solar observables. CAST, the axion solar telescope at CERN, will also dedicate a special data-taking period to the search for streaming DM axions.

    “If true, our findings will provide a totally different view about dark matter, with far-reaching implications in particle and astroparticle physics,” says Zioutas. “Perhaps the demystification of the Sun could lead to a dark-matter solution also.”

    Further reading

    S Bertolucci et al. 2017 Phys. Dark Universe 17 13. Elsevier

    http://www.elsevier.com/locate/dark

    See the full article here .

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