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  • richardmitnick 12:29 pm on September 11, 2019 Permalink | Reply
    Tags: , , , , , Dark Matter   

    From AAS NOVA: “Constraining Collisions of Dark Matter” 

    AASNOVA

    From AAS NOVA

    11 September 2019
    Susanna Kohler

    1
    The Milky Way hosts many small satellite galaxies — similarly to the Andromeda galaxy, pictured here. Could these satellites be a key to constraining the nature of dark matter? [NASA/ESA/Digitized Sky Survey 2/Davide De Martin)]

    Large Magellanic Cloud. Adrian Pingstone December 2003

    smc

    Small Magellanic Cloud. NASA/ESA Hubble and ESO/Digitized Sky Survey 2

    Though dark matter appears to be common in the universe, there’s still a lot we don’t know about it. A new study has now shed some light on this mysterious topic using faint satellite galaxies around the Milky Way.

    2
    The relative amounts of the different constituents of the universe. Dark matter makes up roughly 27%. [ESA/Planck]

    Prolific Yet Unseen

    Our universe is composed almost entirely of dark energy, dark matter, and ordinary matter. While ordinary matter makes up a scant 5% of the universe, dark matter appears to be more common, accounting for 27%. But while dark matter reveals itself through its gravitational effects — adding bulk to galaxy halos that helps hold galaxies together and changes how they move, for instance — we’ve yet to detect it directly.

    This challenge means that we’re still working to understand the nature of this unseen substance. Is dark matter made up of primordial black holes? An as-yet undiscovered subatomic particle? Or something else entirely?

    3
    Strong gravitational lensing like that observed in this image of Abell 1689 provides evidence for dark matter, but we still don’t understand its nature. [NASA/N. Benitez/T. Broadhurst/H. Ford/M. Clampin/G. Hartig/G. Illingworth/the ACS Science Team/ESA]

    The Hunt for the Right Model

    Based on our observations and models of our universe, the standard picture of dark matter is the ΛCDM model, in which dark matter is described as cold (it moves slowly, forming structures only gradually) and collisionless (it doesn’t scatter off of ordinary matter, instead effectively passing through it).

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

    Inflationary Universe. NASA/WMAP

    The cold, collisionless dark-matter model has held up to a number of tests, and it neatly explains the large-scale structure of our universe. But some challenges to the model exist, and astronomers are still considering a number of alternative pictures.

    In a new study led by Ethan Nadler (Kavli Institute for Particle Astrophysics and Cosmology, Stanford University), a team of scientists has now tested alternative theories by asking whether dark matter might not be collisionless, but instead interacts with ordinary matter.

    Suppressing Structure

    Nadler and collaborators point out that alternative models that treat dark matter as a collisional fluid come with a catch: in this picture, as dark matter scatters off of particles in the early universe, heat and momentum are transferred. This transfer smooths out perturbations in the distribution of matter, suppressing the very glitches that would later grow to become small-scale structure in the universe today.

    In effect, the more that dark matter collides with baryons, the less small-scale structure there should be today — limiting the number of low-mass dark-matter halos in our galactic neighborhood and constraining how many small, faint galaxies reside within them.

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

    6
    Upper limits on the velocity-independent dark-matter–proton scattering cross section as a function of dark-matter particle mass. The different shaded regions show values excluded by various observations. The blue shaded exclusion region is the new constraint placed by observations of Milky Way satellites in the current study. [Nadler et al. 2019]

    Collisions Limited

    So what do observations tell us? By combining the observed population of classical and Sloan Digital Sky Survey (SDSS)-discovered Milky-Way satellite galaxies with some clever probabilistic modeling of the population, Nadler and collaborators were able to place strict limits on the scattering cross sections for different-sized dark-matter particles, thereby constraining just how “collisional” dark matter can be.

    The authors’ work continues to support the standard, collisionless picture of dark matter — but there’s plenty of room for deeper constraints. As data arrives from upcoming imaging programs like the Large Synoptic Survey Telescope (LSST), we’re sure to learn more about the small-scale structure of our surroundings and what it means for the nature of mysterious dark matter.

    Citation

    “Constraints on Dark Matter Microphysics from the Milky Way Satellite Population,” Ethan O. Nadler et al 2019 ApJL 878 L32.
    https://iopscience.iop.org/article/10.3847/2041-8213/ab1eb2

    More About Dark Matter

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    The LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes, altitude 2,663 m (8,737 ft),

    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

    LBNL LZ Dark Matter project at SURF, Lead, SD, USA

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
  • richardmitnick 11:50 am on August 24, 2019 Permalink | Reply
    Tags: , , , , , Dark Matter,   

    From Ethan Siegel: “Ask Ethan: Can Black Holes And Dark Matter Interact?” 

    From Ethan Siegel
    Aug 24, 2019

    1.
    A by now iconic illustration of an active black hole, one that accretes matter and accelerates a portion of it outwards in two perpendicular jets. The normal matter undergoing an acceleration like this describes how quasars work extremely well. The matter that falls into a black hole, of any variety, will be responsible for additional growth in both mass and event horizon size for the black hole, whether it’s normal matter or dark matter. (MARK A. GARLICK)

    Black holes are regions of extreme gravity, but dark matter barely interacts at all. Do they play well together?

    Black holes are some of the most extreme objects in the Universe: the only locations where there’s so much energy in a tiny volume of space that an event horizon gets created. When they form, atoms, nuclei, and even fundamental particles themselves are crushed down to an arbitrarily small volume — to a singularity — in our three-dimensional space. At the same time, everything that falls past the event horizon is forever doomed, simply adding to the black hole’s gravitational pull. What does that mean for dark matter? Patreon supporter kilobug asks:

    “How does dark matter interact with black holes? Does it get sucked into the singularity like normal matter, contributing to the mass of the black hole? If so, when the black hole evaporates through Hawking radiation, what happens to [it]?”

    To answer this, we have to start at the beginning: with what a black hole actually is.

    Here on Earth, if you want to send something into space, you need to overcome the Earth’s gravitational pull. The way we normally think about this is in terms of balancing two forms of energy: the gravitational potential energy provided by the Earth itself at its surface, compared with the kinetic energy you’d have to add to your payload to escape from Earth’s gravitational pull.

    If you balance these energies, you can derive your escape velocity: how fast you’d have to make an object go for it to eventually achieve an arbitrarily large distance away from the Earth. Even though the Earth has an atmosphere, providing resistance to that motion and requiring us to impart even more energy to a payload than the escape velocity would imply, escape velocity is still a useful physical concept for us to consider.

    2
    If the Earth had no atmosphere, then firing a cannonball at a particular speed would be enough to determine whether it fell back to Earth (A, B), remained in a stable orbit around Earth (C, D), or escaped from Earth’s gravitational pull (E). For all objects that aren’t black holes, all five of these trajectories are possible. For objects that are black holes, trajectories like C, D, and E are impossible inside the event horizon. (WIKIMEDIA COMMONS USER BRIAN BRONDEL)

    For our planet, that calculated speed — or escape velocity — is somewhere around 25,000 mph (or 11.2 km/s), which the rockets we’ve developed on Earth can actually achieve. Multi-stage rockets have been launching spacecraft beyond the reach of Earth’s gravity since the 1960s, and out of even the Sun’s gravitational reach since the 1970s. But this is still only possible because of how far away we are from the surface of the Sun at the location of Earth’s orbit.

    3
    The very first launch from NASA’s Cape Kennedy space center was of the Apollo 4 rocket. Although it accelerated no faster than a sportscar, the key to its success was that the acceleration was sustained for so long, enabling payloads to escape Earth’s atmosphere and enter orbit. Eventually, multi-stage rockets would enable humans to escape the gravitational pull of the Earth entirely. The Saturn V rockets later took humanity to the Moon. (NASA)

    If we were instead on the surface of the Sun, the speed we’d need to achieve to escape the Sun’s gravitational pull — escape velocity — would be much greater: about 55 times as great, or 617.5 km/s. When our Sun dies, it will contract down to a white dwarf, of about 50% the Sun’s current mass but only the physical size of Earth. In this case, its escape velocity will be about 4.570 km/s, or about 1.5% the speed of light.

    4
    Sirius A and B, a normal (Sun-like) star and a white dwarf star. There are stars that get their energy from gravitational contraction, but they are the white dwarfs, which are millions of times fainter than the stars we’re more familiar with. It wasn’t until we understood nuclear fusion that we began to comprehend how stars shine. (NASA, ESA AND G. BACON (STScI))

    There’s a valuable lesson in comparing the Sun, as it is today, to the Sun’s far-future fate as a white dwarf. As more and more mass gets concentrated into a small region of space, the speed required to escape this object rises. If you allowed that mass density to rise, either by compressing it into a smaller volume or adding more mass to the same volume, your escape velocity would get closer and closer to the speed of light.

    That’s the key limit. Once your escape velocity at the object’s surface reaches or exceeds the speed of light, it isn’t just that light can’t get out, it’s mandatory (in General Relativity) that everything within that object inevitably collapses down to and/or falls into the central singularity. The reason is simple: the fabric of space itself falls towards the central regions faster than the speed of light. Your speed limit is less than the speed at which the space beneath your feet moves, and hence, there’s no escape.

    5
    Both inside and outside the event horizon, space flows like either a moving walkway or a waterfall, depending on how you want to visualize it. At the event horizon, even if you ran (or swam) at the speed of light, there would be no overcoming the flow of spacetime, which drags you into the singularity at the center. Outside the event horizon, though, other forces (like electromagnetism) can frequently overcome the pull of gravity, causing even infalling matter to escape. (ANDREW HAMILTON / JILA / UNIVERSITY OF COLORADO)

    So if you’re at any point away from a central singularity and you’re trying to hold a more distant object up against gravitational collapse, you can’t do it; collapse is inevitable. And the most common way to crest past this limit in the first place is simple: just begin with a star more massive than about 20–40 times the mass of our Sun.

    Like all true stars, it lives its life by burning through the nuclear fuel in its core region. When that fuel gets used up, the center implodes under its own gravity, creating a catastrophic supernova explosion. The outer layers are expelled, but the central region, being massive enough, collapses to a black hole. These “stellar mass” black holes, spanning an approximate range from 8-to-40 solar masses, will grow over time, as they consume any matter or energy that dares to venture too nearby. Even if you move at the speed of light when you cross the event horizon, you’ll never get out again.

    6
    The anatomy of a very massive star throughout its life, culminating in a Type II Supernova. At the end of its life, if the core is massive enough, the formation of a black hole is absolutely unavoidable. (NICOLE RAGER FULLER FOR THE NSF)

    In fact, once you cross the event horizon, it’s an inevitability that you’ll encounter the central singularity. And from the perspective of an outside observer, once you cross the event horizon’s boundary, all you do is add to the mass, energy, charge, and angular momentum of the black hole.

    From outside a black hole, we have no way to gain information about what it was initially composed of. A (neutral) black hole made from protons and electrons, neutrons, dark matter, or even antimatter would all appear identical. In fact, there are only three properties at all that we can observe about a black hole from an external location:

    1.its mass,
    2.its electric charge,
    3.and its angular momentum (or intrinsic rotational spin).

    7
    An iconic illustration of heavily curved spacetime, outside the event horizon of a black hole. As you get closer and closer to the mass’s location, space becomes more severely curved, eventually leading to a location from within which even light cannot escape: the event horizon. The radius of that location is set by the mass, charge, and angular momentum of the black hole, the speed of light, and the laws of General Relativity alone. (PIXABAY USER JOHNSONMARTIN)

    Dark matter, even though we know what it is, is known to have mass but not electric charge.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu The LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes, altitude 2,663 m (8,737 ft),

    The angular momentum it adds to the black hole is entirely dependent on its initial infalling trajectory. If you were interested in other quantum numbers — for example, because you were thinking about the black hole information paradox — you’d be chagrined to learn that dark matter doesn’t have them.

    Dark matter has no color charge, baryon number, lepton number, lepton family number, etc. And because black holes form from the deaths of supermassive stars (i.e., normal, baryonic matter), the initial composition of a newly-formed black hole is always approximately 100% normal matter and 0% dark matter. Even though there’s no definitive way to tell what black holes are made of from the outside alone, we’ve witnessed the direct formation of a black hole from a progenitor star; no dark matter was involved.

    8
    The visible/near-IR photos from Hubble show a massive star, about 25 times the mass of the Sun, that has winked out of existence, with no supernova or other explanation. Direct collapse is the only reasonable candidate explanation, and is one known way, in addition to supernovae or neutron star mergers, to form a black hole for the first time. (NASA/ESA/C. KOCHANEK (OSU)). Two different cameras on Hubble. Image on the left is from WFPC2. Image on the right is from WFC3. Very important and Ethan makes no comment about that.

    NASA/Hubble WFPC2. No longer in service.

    NASA/ESA Hubble WFC3

    There’s a good reason to believe that dark matter doesn’t play a role in the initial formation of black holes, but will play a role in the growth of black holes over time: from the ways it does and does not interact.

    Remember that dark matter interacts only gravitationally, unlike normal matter, which interacts via the gravitational, weak, electromagnetic and strong forces. Yes, there’s perhaps five times as much dark matter total in large galaxies and clusters as there is normal matter, but that’s summed up over the entire huge halo. In a typical galaxy, that dark matter halo extends for a million light-years or more, spherically, in all directions. Contrast that with the normal matter, which is concentrated in a disk that occupies just 0.01% the dark matter’s volume.

    9
    A clumpy dark matter halo with varying densities and a very large, diffuse structure, as predicted by simulations, with the luminous part of the galaxy shown for scale. Since dark matter is everywhere, it should affect the motion of everything around it. The volume occupied by a typical dark matter halo is around 10,000 times as great as the volume occupied by the normal matter. (NASA, ESA, AND T. BROWN AND J. TUMLINSON (STScI))

    Black holes tend to form in the inner regions of the galaxy, where the normal matter is dominant over dark matter. Consider just the region of space where we’re located: around our Sun. If we drew a sphere that was 100 AU in radius (where one AU is the distance of the Earth from the Sun) around our Solar System, we’d enclose all the planets, moons, asteroids and pretty much the entire Kuiper belt. We’d also enclose a fair amount of dark matter in that volume.

    Quantitatively, though, the baryonic mass — the normal matter — inside this sphere would be dominated by our Sun, and would weigh about 2 × 10³⁰ kg. (Everything else, combined, adds just another 0.2% to that total.) On the other hand, the total amount of dark matter in that same sphere? Only about 1 × 10¹⁹ kg, or just 0.0000000005% the mass of the normal matter in that same region. All the dark matter combined is about the same mass as a modest asteroid like Juno.

    10
    In the solar system, to a first approximation, the Sun determines the orbits of the planets. To a second approximation, all the other masses (like planets, moons, asteroids, etc.) play a large role. But to add in dark matter, we’d have to get incredibly sensitive: the entire contribution of all the dark matter within 100 AU of the Sun is about the same contribution as the mass of Juno, the asteroid belt’s 11th largest asteroid (by volume). (WIKIPEDIA USER DREG743)

    Over time, dark matter and normal matter both will collide with this black hole, getting absorbed and adding to its mass. The vast majority of black hole mass growth will come from normal matter and not dark matter, although at some point, about 10²² years into the future, the rate of black hole decay will finally surpass the rate of black hole growth.

    The Hawking radiation process results in the emission of particles and photons from outside the black hole’s event horizon, conserving all the energy, charge and angular momentum from the black hole’s insides. Perhaps the information encoded on the surface is somehow encoded in the radiation, too: this is the essence of the black hole information paradox.

    11
    Encoded on the surface of the black hole can be bits of information, proportional to the event horizon’s surface area. When the black hole decays, it decays to a state of thermal radiation. Whether that information survives and is encoded in the radiation or not, and if so, how, is not a question that our current theories can provide the answer to. (T.B. BAKKER / DR. J.P. VAN DER SCHAAR, UNIVERSITEIT VAN AMSTERDAM)

    This process may take anywhere from 10⁶⁷ to 10¹⁰⁰ years, depending on the black hole’s mass. But what comes out is simply thermal, blackbody radiation.

    This means that some dark matter will come out of black holes, but that’s expected to be completely independent of whether a substantial amount of dark matter went into the black hole in the first place. All a black hole has memory of, once things have fallen in, is a small set of quantum numbers, and the amount of dark matter that went into it isn’t one of them. What comes out, at least in terms of particle content, isn’t going to be the same as what you put in!

    12
    The event horizon of a black hole is a spherical or spheroidal region from which nothing, not even light, can escape. Although conventional blackbody radiation is emitted from outside the event horizon, it is unclear where, when, or how the entropy/information encoded on the surface behaves in a merger scenario. (NASA; DANA BERRY, SKYWORKS DIGITAL, INC.)

    If you do the math, you’ll find that black holes will use both normal matter and dark matter as a food source, but that normal matter will dominate the rate of growth of the black hole, even over long, cosmic timescales. When the Universe is more than a billion times as old as it is today, black holes will still owe more than 99% of their mass to normal matter, and less than 1% to dark matter.

    Dark matter is neither a good food source for black holes, nor is it (information-wise) an interesting one. What a black hole gains from eating dark matter is no different than what it gains from shining a flashlight into it. Only the mass/energy content, like you’d get from E = mc², matters. Black holes and dark matter do interact, but their effects are so small that even ignoring dark matter entirely still gives you a great description of black holes: past, present, and future.

    See the full article here .

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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 9:02 am on August 16, 2019 Permalink | Reply
    Tags: , , , , Dark Matter, , , Tracy Slatyer,   

    From MIT News: Women in STEM-“Data-mining for dark matter” Tracy Slatyer 

    MIT News

    From MIT News

    August 15, 2019
    Jennifer Chu

    1
    Associate professor Tracy Slatyer focuses on searching through telescope data for signals of mysterious phenomena such as dark matter, the invisible stuff that makes up more than 80 percent of the matter in the universe but has only been detected through its gravitational pull. In her teaching, she seeks to draw out and support a new and diverse crop of junior scientists. Images: Bryce Vickmark

    2
    Tracy Slatyer. Quanta.

    When Tracy Slatyer faced a crisis of confidence early in her educational career, Stephen Hawking’s A Brief History of Time and a certain fictional janitor at MIT helped to bolster her resolve.

    Slatyer was 11 when her family moved from Canberra, Australia, to the island nation of Fiji. It was a three-year stay, as part of her father’s work for the South Pacific Forum, an intergovernmental organization.

    “Fiji was quite a way behind the U.S. and Australia in terms of gender equality, and for a girl to be interested in math and science carried noticeable social stigma,” Slatyer recalls. “I got bullied quite a lot.”

    She eventually sought guidance from the school counselor, who placed the blame for the bullying on the victim herself, saying that Slatyer wasn’t sufficiently “feminine.” Slatyer countered that the bullying seemed to be motivated by the fact that she was interested in and good at math, and she recalls the counselor’s unsympathetic advice: “Well, yes, honey, that’s a problem you can fix.”

    “I went home and thought about it, and decided that math and science were important to me,” Slatyer says. “I was going to keep doing my best to learn more, and if I got bullied, so be it.”

    She doubled down on her studies and spent a lot of time at the library; she also benefited from supportive parents, who gave her Hawking’s groundbreaking book on the origins of the universe and the nature of space and time.

    “It seemed like the language in which these ideas could most naturally be described was that of mathematics,” Slatyer says. “I knew I was pretty good at math. And learning that that talent was potentially something I could apply to understanding how the universe worked, and maybe how it began, was very exciting to me.”

    Around this same time, the movie Good Will Hunting came out in theaters. The story, of a townie custodian at MIT who is discovered as a gifted mathematician, had a motivating impact on Slatyer.

    “What my 13-year-old self took out of this was, MIT was a place where, if you were talented at math, people would see that as a good thing rather than something to be stigmatized, and make you welcome — even if you were a janitor or a little girl from Fiji,” Slatyer says. “It was my first real indication that such places might exist. Since then, MIT has been an important symbol to me, of valuing intellectual inquiry and being willing to accept anyone in the world.”

    This year, Slatyer received tenure at MIT and is now the Jerrold R. Zacharias Associate Professor of Physics and a member of the Center for Theoretical Physics and the Laboratory for Nuclear Science. She focuses on searching through telescope data for signals of mysterious phenomena such as dark matter, the invisible stuff that makes up more than 80 percent of the matter in the universe but has only been detected through its gravitational pull. In her teaching, she seeks to draw out and support a new and diverse crop of junior scientists.

    “If you want to understand how the universe works, you want the very best and brightest people,” Slatyer says. “It’s essential that theoretical physics becomes more inclusive and welcoming, both from a moral perspective and to get the best science done.”

    Connectivity

    Slatyer’s family eventually moved back to Canberra, where she dove eagerly into the city’s educational opportunities.

    After earning an undergraduate degree from the Australian National University, followed by a brief stint at the University of Melbourne, Slatyer was accepted to Harvard University as a physics graduate student. Her interests were slowly gravitating toward particle physics, but she was unsure about which direction to take. Then, two of her mentors put her in touch with a junior faculty member, Doug Finkbeiner, who was leading a project to mine astrophysical data for signals of new physics.

    At the time, much of the physics community was eagerly anticipating the start-up of the Large Hadron Collider and the release of data on particle interactions at high energies, which could potentially reveal physics beyond the Standard Model.

    In contrast, telescopes have long made public their own data on astrophysical phenomena. What if, instead of looking through these data for objects such as black holes and neutron stars that evolved over millions of years, one could comb through it for signals of more fundamental mysteries, such as hints of new elementary particles and even dark matter?

    The prospects were new and exciting, and Slatyer promptly took on the challenge.

    “Chasing that feeling”

    In 2008, the Fermi Gamma-Ray Space Telescope launched, giving astronomers a new view of the cosmos in the gamma-ray band of the electromagnetic spectrum, where high-energy astrophysical phenomena can be seen.

    NASA/Fermi LAT


    NASA/Fermi Gamma Ray Space Telescope

    Slatyer and Finkbeiner proposed that Fermi’s data might also reveal signals of dark matter, which could theoretically produce high-energy electrons when dark matter particles collide.

    In 2009, Fermi made its data available to the public, and Slatyer and Finkbeiner —together with Harvard postdoc Greg Dobler and collaborators at New York University — put their mining tools to work as soon as the data were released online.

    The group eventually constructed a map of the Milky Way galaxy, shining in gamma rays, and revealed a fuzzy, egg-like shape. Upon further analysis, led by Slatyer’s fellow PhD student Meng Su, this fuzzy “haze” coalesced into a figure-eight, or double-bubble structure, extending some 25,000 light-years above and below the disc of the Milky Way. Such a structure had never been observed before. The group named the mysterious structure the “Fermi bubbles,” after the telescope that originally observed it.

    “It was really special — we were the first people in the history of the world to be able to look at the sky in this way and understand that this structure was there,” Slatyer says. “That’s a really incredible feeling, and chasing that feeling is something that inspires and motivates me, and I think many scientists.”

    Searching for the invisible

    Today, Slatyer continues to sift through Fermi data for evidence of dark matter. The Fermi Bubbles’ distinctive shape makes it unlikely they are associated with dark matter; they are more likely to reveal a past eruption from the giant black hole at the Milky Way’s center, or outflows fueled by exploding stars. However, other signals are more promising.

    Around the center of the Milky Way, where dark matter is thought to concentrate, there is a glow of gamma rays. In 2013, Slatyer, her first PhD student Nicholas Rodd, and collaborators at Harvard University and Fermilab showed this glow had properties similar to what theorists would expect if dark matter particles were colliding and producing visible light. However, in 2015, Slatyer and collaborators at MIT and Princeton University challenged this interpretation with a new analysis, showing that the glow was more consistent with originating from a new population of spinning neutron stars called pulsars.

    But the case is not quite closed. Recently, Slatyer and MIT postdoc Rebecca Leane reanalyzed the same data, this time injecting a fake dark matter signal into the data, to see whether the techniques developed in 2015 could detect dark matter if it were there. But the signal was missed, suggesting that if there were other, actual signals of dark matter in the Fermi data, they could have been missed as well.

    Slatyer is now improving on data mining techniques to better detect dark matter in the Fermi data, along with other astrophysical open data. But she won’t be discouraged if her search comes up empty.

    “There’s no guarantee there is a dark matter signal,” Slatyer says. “But if you never look, you’ll never know. And in searching for dark matter signals in these datasets, you learn other things, like that our galaxy contains giant gamma-ray bubbles, and maybe a new population of pulsars, that no one ever knew about. If you look closely at the data, the universe will often tell you something new.”

    See the full article here .


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    Please help promote STEM in your local schools.


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    MIT Seal

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  • richardmitnick 11:44 am on August 13, 2019 Permalink | Reply
    Tags: , DAMA/LIBRA at Gran Sasso searching for WIMPS., Dark Matter, , , , Two new experiments ANAIS and COSINE-100 are looking for WIMPs.   

    From Symmetry: “Testing DAMA” 

    Symmetry Mag
    From Symmetry

    08/13/19
    Jim Daley

    An Italian experiment has a 20-year signal of what could be dark matter—and scientists are embarking on their most promising efforts yet to confirm or refute its results.

    1
    Illustration by Sandbox Studio, Chicago

    For more than two decades, a detector deep beneath the Apennine Mountains in Italy has observed a regularly changing signal that its operators think comes from our planet’s movements through the “halo” of dark matter suffusing the Milky Way galaxy.

    Dark matter—a substance that scientists have otherwise only indirectly detected—is thought to make up 85% of the matter in the universe. DAMA, an experiment at the Gran Sasso National Laboratory in Italy, has since 1997 reported findings consistent with its discovery. But there has not been an overwhelming consensus in the physics community that they’ve found it.

    DAMA-LIBRA at Gran Sasso

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy

    DAMA/LIBRA—the full name of the current generation of the experiment—released its most recent results in 2018. Like previous data, those findings show a signal that cycles annually, peaking in around June 2.

    This so-called annual modulation is what we would expect to see happen with a dark matter signal collected on Earth. Our planet orbits the sun, which in turn moves through the Milky Way. Half of the year they’re moving in the same direction, increasing the speed with which the Earth should pass through our galaxy’s dark matter; the other half they’re moving in opposite directions, making that speed slower.

    An observatory on Earth should move faster through any dark matter halo in spring than fall, resulting in an uptick in the rate of particle detection. “The effect is like a dark matter headwind,” says Jason Kumar, a physicist at the University of Hawaii at Manoa. In the Northern Hemisphere, “you would expect it to peak in June, and then see a dip in the event rate in the winter.”

    Scientists don’t know exactly what dark matter is. One candidate DAMA is searching for: WIMPs, or weakly interacting massive particles. Sodium iodide crystals in DAMA’s detectors emit bursts of radiation whenever a particle (possibly a WIMP) collides with the crystals’ atomic nuclei. DAMA’s signal shows these bursts occurring in the annual cycle physicists would expect to see.

    Rita Bernabei, a physicist at the University of Rome Tor Vergata and the longtime leader of DAMA, says the experiment’s signal indicates the presence of dark matter particles in the galactic halo. “There are no alternative explanations for the observed signal,” Bernabei says.

    There is still some room for doubt, though: Unaccounted-for seasonal variations in environmental conditions at Gran Sasso could be causing the modulation, for example. Or it could be “systematics,” a catch-all shorthand physicists use to refer to errors in equipment calibration or experimental design. Adding to the skepticism is the fact that other dark matter detectors have yet to confirm what DAMA is seeing. But that could soon change.

    Two new experiments, ANAIS and COSINE-100, are also looking for WIMPs in the galactic halo—and unlike other experiments that have attempted to verify DAMA’s signal, they’re using DAMA’s same detection material, sodium iodide.

    2
    ANAIS

    COSINE-100 at Yangyang underground laboratory in South Korea

    ANAIS, a Spanish detector that is effectively a smaller version of DAMA, began collecting data in 2017. In the next few years the project should start to have statistically significant results, says ANAIS spokesperson Marisa Sarsa, a physicist at the University of Zaragoza, Spain. “If we find a similar signal with annual modulation, it will really be quite an impact,” she says.

    If ANAIS finds no signal, Sarsa says the challenge will then be to determine what is actually causing the annual modulation observed by DAMA.

    COSINE-100 has been taking data since 2016. Located in South Korea, that experiment’s sodium iodide crystals are submerged in 2000 liters of liquid to help reduce background noise that can complicate analysis. The experiment will have enough data to search for modulation by about 2021.

    In July 2019, Reina Maruyama, a professor of physics at Yale University, was awarded a National Science Foundation grant to test DAMA’s results with the COSINE experiment. “With five years of running the experiment, if the signal is there, we should be able to see it,” Maruyama says. “If it’s not there—and this is a little harder to do, but—we’ll be able to refute it.”

    If COSINE or ANAIS does see a signal that appears to confirm DAMA’s results, the next step would be to confirm the finding with a detector in the Southern hemisphere. Construction is slated to begin this fall on an experiment named SABRE, a dark matter detector that will be located in a former gold mine in western Australia.

    A confirmation that DAMA is indeed seeing dark matter would open another gold mine of sorts. Katherine Freese, a theoretical astrophysicist at the University of Texas, first proposed the technique of searching for an annual modulation of the dark matter signal in the galactic halo in 1986. Freese says that if the DAMA signal is confirmed, physicists would then have to start exploring the properties of the particles making the signal. “You would try to figure out what is the mass of the particle, what is the scattering strength of the particle, and what is the interaction [with the detector], in detail,” she says. “And then we’ll keep going with other experiments until we figure out exactly what its details are.”

    Meanwhile, DAMA/LIBRA is still taking data. Researchers at Gran Sasso are developing a new phase of the experiment that will increase the instrument’s sensitivity and decrease its energy threshold. Their goals, Bernabei says, are to improve the precision on the dark matter annual modulation parameters, potentially disentangle various scenarios that could explain the mysterious signal, and possibly explore a joint detection of its annual modulation.

    Whatever ANAIS and COSINE-100 do ultimately find, pinning down the source of the mysterious annually cycling signal will be a major step forward in the search for dark matter in the Milky Way.

    “If we don’t see anything, then I think the community can really move on and focus on clearing up the dark matter landscape,” Maruyama says. “If we see a signal?” She pauses, considering the consequence of confirming DAMA after all these years. “I think we’d really open up the field. And that’s really exciting.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:35 pm on August 10, 2019 Permalink | Reply
    Tags: "Physicists Working to Discover New Particles, , , , Dark Matter, , , Texas Tech, The LDMX Experiment   

    From Texas Tech via FNAL: “Physicists Working to Discover New Particles, Dark Matter” 

    1

    From TEXAS TECH UNIVERSITY

    via

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    August 5, 2019
    Glenys Young, Texas Tech

    Faculty recently presented their work at the European Physical Society’s 2019 Conference on High Energy Physics.

    Texas Tech University is well known for its research on topics that hit close to home for us here on the South Plains, like agriculture, water use and climate. But Texas Tech also is making its name known among those who study the farthest reaches of space and the mysteries of matter.

    Faculty from the Texas Tech Department of Physics & Astronomy recently presented at the European Physical Society’s 2019 Conference on High Energy Physics on the search for dark matter and other new particles that could help unlock the history and nature of the universe.

    New ways to approach the most classical search for new particles.

    Texas Tech, led by professor and department chair Sung-Won Lee, has been playing a leading role in new-particle hunt for more than a decade. As part of the Compact Muon Solenoid (CMS) experiment, which investigates a wide range of physics, including the search for extra dimensions and particles that could make up dark matter, Lee has led the new-particle search at the European Organization for Nuclear Research (CERN).

    1
    Lee

    “Basically, we’re looking for any experimental evidence of new particles that could open the door to whole new realms of physics that researchers believe could be there,” Lee said. “Researchers at Texas Tech are continuing to look for elusive new particles in the CMS experiment at CERN’s Large Hadron Collider (LHC), and if found, we could answer some of the most profound questions about the structure of matter and the evolution of the early universe.”

    The LHC essentially bounces around tiny particles at incredibly high speeds to see what happens when the particles collide. Lee’s search focuses on identifying possible hints of new physics that could add more subatomic particles to the Standard Model of particle physics.

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector


    CMS

    CERN CMS New

    LHCb
    CERN LHCb New II

    “The Standard Model has been enormously successful, but it leaves many important questions unanswered,” Lee said.

    Standard Model of Particle Physics

    “It is also widely acknowledged that, from the theoretical standpoint, the Standard Model must be part of a larger theory, ‘Beyond the Standard Model’ (BSM), which is yet to be experimentally confirmed.”

    Some BSM theories suggest that the production and decay of new particles could be observed in the LHC by the resulting highly energetic jets that shoot out in opposite directions (dijets) and the resonances they leave. Thus the search for new particles depends on the search for these resonances. In some ways, it’s like trying to trace air movements to find a fan you can’t see, hear or touch.

    In 2018-19, in collaboration with the CMS group, Texas Tech’s team performed a search for narrow dijet resonances using a newly available dataset at the LHC. The data were consistent with the Standard Model predictions, and no significant deviations from the pure background hypothesis were observed. But one spectacular collision was recorded in which the masses of the two jets were the same. This evidence allows for the possibility that the jets originated from BSM-hypothesized particle decay.

    “Since the LHC is the highest energy collider currently in operation, it is crucial to pay special attention to the highest-dijet-mass events where first hints of new physics at higher energies could start to appear,” Lee said. “This unusual high-mass event could likely be a collision created by the Standard Model background or possibly the first hint of new physics, but with only one event in hand, it is not possible to say which.”

    For now, Lee, postdoctoral research fellow Federico De Guio and doctoral student Zhixing (Tyler) Wang are working to update the dijet resonance search using the full LHC dataset and extend the scope of the analysis.

    “This extension of the search could help prove space-time-matter theory, which requires the existence of several extra spatial dimensions to the universe,” Lee said. “I believe that, with our extensive research experience, Texas Tech’s High Energy Physics group can contribute to making such discoveries.”

    Enhancing the missing momentum microscope

    Included in the ongoing new-particle search using the LHC is the pursuit of dark matter, an elusive, invisible form of matter that dominates the matter content of the universe.

    “Currently, the LHC is producing the highest-energy collisions from an accelerator in the world, and my primary research interest is in understanding whether or not new states of matter are being produced in these collisions,” said Andrew Whitbeck, an assistant professor in the Department of Physics & Astronomy.

    4
    Whitbeck

    “Specifically, we are looking for dark matter produced in association with quarks, the constituents of the proton and neutron. These signatures are important for both understanding the nature of dark matter, but also the nature of the Higgs boson, a cornerstone of our theory for how elementary particles interact.”

    The discovery of the Higgs boson at the LHC in 2012 was a widely celebrated accomplishment of the LHC and the detector collaborations involved.

    Peter Higgs


    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    However, the mere existence of the Higgs boson has provoked a lot of questions about whether there are new particles that could help us better understand the Higgs boson and other questions, like why gravity is so weak compared to other forces.

    As an offshoot of that finding, Whitbeck has been working to better understand a type of particle called neutrinos.

    “Neutrinos are a unique particle in the catalog of known particles in that they are the lightest matter particles, and they only can interact with particles via the Weak force, which, as its name suggests, only produces a feeble force between neutrinos and other matter,” Whitbeck said. “Neutrinos are so weakly interacting at the energies produced by the LHC that it is very likely a neutrino travels through the entire earth without deviating from its initial trajectory.

    “Dark matter is expected to behave similarly given that, despite being all around us, we don’t directly see it. This means that in looking for dark matter produced in proton-proton collisions, we often find lots of neutrinos. Understanding how many events with neutrinos there are is an important first step to understanding if there are events with dark matter.”

    Since the discovery of the Higgs boson, many of the most obvious signatures have come up empty for any signs of dark matter, and the latest results are some of the most sensitive measurements done to date. However, Whitbeck and his fellow scientists will continue to look for many more subtle signatures as well as a very powerful signature in which dark matter hypothetically is produced almost by itself, with only one lonely proton fragment visible in the event. The strategy provides powerful constraints for the most difficult-to-see models of dark matter.

    “With all of the traditional ways of searching for dark matter in proton-proton collisions turning up empty, I have also been working to design a new experiment, the Light Dark Matter eXperiment (LDMX), that will employ detector technology and techniques similar to what is used at CMS to look for dark matter,” Whitbeck said.

    6
    Texas Tech The LDMX Experiment schematic

    “One significant difference is that LDMX will look at electrons bombarding a target. If the mass of dark matter is somewhere between the mass of the electron and the mass of the proton, this experiment will likely be able to see it.”

    Texas Tech also is working to upgrade the CMS detector so it can handle much higher rates of collisions after the LHC undergoes some upgrades of its own. The hope is that with higher rates, they’ll be able to see not only new massive particles but also the rarest of processes, such as the production of two Higgs bosons. This detector construction is ramping up now at Texas Tech’s new Advanced Physics Detector Laboratory at Reese Technology Center.

    Besides being a background for dark matter searches, neutrinos also are a growing focus of research in particle physics. Even now, the Fermi National Accelerator Laboratory is able to produce intense beams of neutrinos that can be used to study their idiosyncrasies, but there are plans to upgrade the facility to produce the most intense beams of neutrinos ever and to place the most sensitive neutrino detectors nearby, making the U.S. the center of neutrino physics.

    FNAL/NOvA experiment map

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    Measurements done with these neutrinos could unlock whether these particles play a big role in the creation of a matter-dominated universe.

    Texas Tech’s High Energy Physics group hopes that, in the near future, it can help tackle some of the challenges this endeavor presents.

    See the full here.


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    FNAL Icon

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

     
  • richardmitnick 11:19 am on August 8, 2019 Permalink | Reply
    Tags: , , , , , Dark Matter, , , ,   

    From Johns Hopkins University via Science Alert: “Fascinating New Study Claims Dark Matter May Be Older Than The Big Bang” 

    Johns Hopkins
    From Johns Hopkins University

    via

    ScienceAlert

    Science Alert

    8 AUG 2019
    MICHELLE STARR

    1
    A simulated map of dark matter. (Tom Abel & Ralf Kaehler/KIPAC/SLAC/AMNH)

    Dark matter might well be the biggest mystery in the Universe. We know there’s something out there making things move faster than they should. But we don’t know what it is, and we sure as heck don’t know where it came from.

    According to a new paper [below], the origins of dark matter may be more peculiar than we know. Perhaps, they were particles that appeared in a very brief period of time, just fractions of fractions of a second, before the Big Bang.

    This doesn’t just suggest a new connection between particle physics and astronomy; if this hypothesis holds, it could indicate a new way to search for the mysterious stuff.

    “If dark matter consists of new particles that were born before the Big Bang, they affect the way galaxies are distributed in the sky in a unique way,” said astronomer and physicist Tommi Tenkanen of Johns Hopkins University.

    “This connection may be used to reveal their identity and make conclusions about the times before the Big Bang too.”

    It’s all tangled up with the order of events at the beginning of the Universe, which in itself is a pretty murky period of time.

    We think there was something called the Big Bang – although precisely what that entailed is still being debated. And we think there was something called cosmic inflation, a very brief period of time – a fraction of a second so small we don’t have a name for it – in which the Universe blew up like a balloon.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

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

    Alan Guth’s notes:

    Alan Guth’s original notes on inflation

    3
    (Drbogdan/Yinweichen/Wikimedia Commons)

    It seems more generally accepted that this occurred between around 10^-36 and 10^-32 seconds after the Big Bang. That model of inflation looks like the image above.

    But some scientists think it happened just before the Big Bang, in which case the Big Bang is the name given to the conditions in the Universe right at the end of inflation.

    At this stage we just have no way of knowing. As Harvard-Smithsonian theoretical physicist Avi Loeb said earlier this year, “the current situation for inflation is that it’s such a flexible idea, it cannot be falsified experimentally.” He was talking about whether or not cosmic inflation actually happened (also a matter of debate), but the statement works for the timing of the whoompf, too.

    Dark matter – which, according to our calculations, makes up around 80 percent of the matter in the Universe – is sometimes considered to be a product of the Big Bang.

    But “if dark matter were truly a remnant of the Big Bang, then in many cases researchers should have seen a direct signal of dark matter in different particle physics experiments already,” Tenkanen states.

    Instead, his mathematical modelling suggests that dark matter could have been a product of cosmic inflation. It’s not the first time this idea has been proposed, but Tenkanen has provided the maths that support it.

    And, if cosmic inflation occurred before the Big Bang, dark matter could have been around before the rest of the stuff in the primordial Universe Soup.

    This suggests that scalar particles could lead us to dark matter. These are particles with a spin of zero, and the inflaton theory – whereby a scalar field drove cosmic inflation – suggests that they were produced in abundance during this eyeblink of time.

    So far, we’ve only ever detected one scalar particle, the Higgs boson.

    Peter Higgs


    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    But that wouldn’t be able to tell us much about dark matter in and of itself anyway.

    “While this type of dark matter is too elusive to be found in particle experiments, it can reveal its presence in astronomical observations,” Tenkanen said.

    “We will soon learn more about the origin of dark matter when the Euclid satellite is launched in 2022.

    ESA/Euclid spacecraft

    It’s going to be very exciting to see what it will reveal about dark matter and if its findings can be used to peak into the times before the Big Bang.”

    It’s all highly theoretical stuff, but it’s about as good a lead as any on the mysterious matter that’s playing a key role in shaping our Universe. It’ll be fascinating to see how the search for dark matter plays out in the coming decade.

    The research has been published in Physical Review Letters.

    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 1:27 pm on August 2, 2019 Permalink | Reply
    Tags: "We Have Already Entered The Sixth And Final Era Of Our Universe", , , , , , Dark Matter, ,   

    From Ethan Siegel: “We Have Already Entered The Sixth And Final Era Of Our Universe” 

    From Ethan Siegel
    Aug 2, 2019

    Timeline of the Inflationary Universe WMAP

    From the inflationary state that preceded the Big Bang to our cold, lonely, dark energy-dominated fate, the Universe goes through six different eras. We’re living in the last one already.

    The Universe is not the same today as it was yesterday. With each moment that goes by, a number of subtle but important changes occur, even if many of them are imperceptible on measurable, human timescales. The Universe is expanding, which means that the distances between the largest cosmic structures are increasing with time.

    A second ago, the Universe was slightly smaller; a second from now, the Universe will be slightly larger. But those subtle changes both build up over large, cosmic timescales, and affect more than just distances. As the Universe expands, the relative importance of radiation, matter, neutrinos, and dark energy all change. The temperature of the Universe changes. And what you’d see in the sky would change dramatically as well. All told, there are six different eras we can break the Universe into, and we’re already in the final one.

    2
    How matter (top), radiation (middle), and a cosmological constant (bottom) all evolve with time in an expanding Universe. As the Universe expands, the matter density dilutes, but the radiation also becomes cooler as its wavelengths get stretched to longer, less energetic states. Dark energy’s density, on the other hand, will truly remain constant if it behaves as is currently thought: as a form of energy intrinsic to space itself. (E. SIEGEL / BEYOND THE GALAXY)

    The reason for this can be understood from the graph above. Everything that exists in our Universe has a certain amount of energy in it: matter, radiation, dark energy, etc. As the Universe expands, the volume that these forms of energy occupy changes, and each one will have its energy density evolve differently. In particular, if we define the observable horizon by the variable a, then:

    matter will have its energy density evolve as 1/a³, since (for matter) density is just mass over volume, and mass can easily be converted to energy via E = mc²,
    radiation will have its energy density evolve as 1/a⁴, since (for radiation) the number density is the number of particles divided by volume, and the energy of each individual photon stretches as the Universe expands, adding an additional factor of 1/a relative to matter,
    and dark energy is a property of space itself, so its energy density remains constant (1/a⁰), irrespective of the Universe’s expansion or volume.

    3
    A visual history of the expanding Universe includes the hot, dense state known as the Big Bang and the growth and formation of structure subsequently. The full suite of data, including the observations of the light elements and the cosmic microwave background, leaves only the Big Bang as a valid explanation for all we see. As the Universe expands, it also cools, enabling ions, neutral atoms, and eventually molecules, gas clouds, stars, and finally galaxies to form. (NASA / CXC / M. WEISS)

    A Universe that has been around longer, therefore, will have expanded more. It will be cooler in the future and was hotter in the past; it was gravitationally more uniform in the past and is clumpier now; it was smaller in the past and will be much, much larger in the future.

    By applying the laws of physics to the Universe, and comparing the possible solutions with the observations and measurements we’ve obtained, we can determine both where we came from and where we’re headed. We can extrapolate our past history all the way back to the beginning of the hot Big Bang and even before, to a period of cosmic inflation. We can extrapolate our current Universe into the far distant future as well, and foresee the ultimate fate that awaits everything that exists.

    4
    Our entire cosmic history is theoretically well-understood, but only because we understand the theory of gravitation that underlies it, and because we know the Universe’s present expansion rate and energy composition. Light will always continue to propagate through this expanding Universe, and we will continue to receive that light arbitrarily far into the future, but it will be limited in time as far as what reaches us. We will need to probe to fainter brightnesses and longer wavelengths to continue to see the objects presently visible, but those are technological, not physical, limitations. (NICOLE RAGER FULLER / NATIONAL SCIENCE FOUNDATION)

    When we draw the dividing lines based on how the Universe behaves, we find that there are six different eras that will come to pass.

    Inflationary era: which preceded and set up the hot Big Bang.
    Primordial Soup era: from the start of the hot Big Bang until the final transformative nuclear & particle interactions occur in the early Universe.
    Plasma era: from the end of non-scattering nuclear and particle interactions until the Universe cools enough to stably form neutral matter.
    Dark Ages era: from the formation of neutral matter until the first stars and galaxies reionize the intergalactic medium of the Universe completely.
    Stellar era: from the end of reionization until the gravity-driven formation and growth of large-scale structure ceases, when the dark energy density dominates over the matter density.
    Dark Energy era: the final stage of our Universe, where the expansion accelerates and disconnected objects speed irrevocably and irreversibly away from one another.

    We already entered this final era billions of years ago. Most of the important events that will define our Universe’s history have already occurred.

    5
    Fluctuations in spacetime itself at the quantum scale get stretched across the Universe during inflation, giving rise to imperfections in both density and gravitational waves. Whether inflation arose from an eventual singularity or not is unknown, but the signatures of whether it occurred are accessible in our observable Universe. (E. SIEGEL, WITH IMAGES DERIVED FROM ESA/PLANCK AND THE DOE/NASA/ NSF INTERAGENCY TASK FORCE ON CMB RESEARCH)

    1.) Inflationary era. Prior to the hot Big Bang, the Universe wasn’t filled with matter, antimatter, dark matter or radiation. It wasn’t filled with particles of any type. Instead, it was filled with a form of energy inherent to space itself: a form of energy that caused the Universe to expand both extremely rapidly and relentlessly, in an exponential fashion.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

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

    Alan Guth’s notes:

    Alan Guth’s original notes on inflation

    It stretched the Universe, from whatever geometry it once had, into a state indistinguishable from spatially flat.
    It expanded a small, causally connected patch of the Universe to one much larger than our presently visible Universe: larger than the current causal horizon.
    It took any particles that may have been present and expanded the Universe so rapidly that none of them are left inside a region the size of our visible Universe.
    And the quantum fluctuations that occurred during inflation created the seeds of structure that gave rise to our vast cosmic web today.

    And then, abruptly, some 13.8 billion years ago, inflation ended. All of that energy, once inherent to space itself, got converted into particles, antiparticles, and radiation. With this transition, the inflationary era ended, and the hot Big Bang began.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    6
    At the high temperatures achieved in the very young Universe, not only can particles and photons be spontaneously created, given enough energy, but also antiparticles and unstable particles as well, resulting in a primordial particle-and-antiparticle soup. Yet even with these conditions, only a few specific states, or particles, can emerge. (BROOKHAVEN NATIONAL LABORATORY)

    2.) Primordial Soup era. Once the expanding Universe is filled with matter, antimatter and radiation, it’s going to cool. Whenever particles collide, they’ll produce whatever particle-antiparticle pairs are allowed by the laws of physics. The primary restriction comes only from the energies of the collisions involved, as the production is governed by E = mc².

    As the Universe cools, the energy drops, and it becomes harder and harder to create more massive particle-antiparticle pairs, but annihilations and other particle reactions continue unabated. 1-to-3 seconds after the Big Bang, the antimatter is all gone, leaving only matter behind. 3-to-4 minutes after the Big Bang, stable deuterium can form, and nucleosynthesis of the light elements occurs. And after some radioactive decays and a few final nuclear reactions, all we have left is a hot (but cooling) ionized plasma consisting of photons, neutrinos, atomic nuclei and electrons.

    7
    At early times (left), photons scatter off of electrons and are high-enough in energy to knock any atoms back into an ionized state. Once the Universe cools enough, and is devoid of such high-energy photons (right), they cannot interact with the neutral atoms, and instead simply free-stream, since they have the wrong wavelength to excite these atoms to a higher energy level. (E. SIEGEL / BEYOND THE GALAXY)

    3.) Plasma era. Once those light nuclei form, they’re the only positively (electrically) charged objects in the Universe, and they’re everywhere. Of course, they’re balanced by an equal amount of negative charge in the form of electrons. Nuclei and electrons form atoms, and so it might seem only natural that these two species of particle would find one another immediately, forming atoms and paving the way for stars.

    Unfortunately for them, they’re vastly outnumbered — by more than a billion to one — by photons. Every time an electron and a nucleus bind together, a high-enough energy photon comes along and blasts them apart. It isn’t until the Universe cools dramatically, from billions of degrees to just thousands of degrees, that neutral atoms can finally form. (And even then, it’s only possible because of a special atomic transition.)

    At the beginning of the Plasma era, the Universe’s energy content is dominated by radiation. By the end, it’s dominated by normal and dark matter.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    This third phase takes us to 380,000 years after the Big Bang.

    9
    Schematic diagram of the Universe’s history, highlighting reionization. Before stars or galaxies formed, the Universe was full of light-blocking, neutral atoms. While most of the Universe doesn’t become reionized until 550 million years afterwards, with some regions achieving full reionization earlier and others later. The first major waves of reionization begin happening at around 250 million years of age, while a few fortunate stars may form just 50-to-100 million years after the Big Bang. With the right tools, like the James Webb Space Telescope, we may begin to reveal the earliest galaxies.(S. G. DJORGOVSKI ET AL., CALTECH DIGITAL MEDIA CENTER)

    4.) Dark Ages era. Filled with neutral atoms, at last, gravitation can begin the process of forming structure in the Universe. But with all these neutral atoms around, what we presently know as visible light would be invisible all throughout the sky.

    Why’s that? Because neutral atoms, particularly in the form of cosmic dust, are outstanding at blocking visible light.

    In order to end these dark ages, the intergalactic medium needs to be reionized. That requires enormous amounts of star-formation and tremendous numbers of ultraviolet photons, and that requires time, gravitation, and the start of the cosmic web. The first major regions of reionization take place 200–250 million years after the Big Bang, but reionization doesn’t complete, on average, until the Universe is 550 million years old. At this point, the star-formation rate is still increasing, and the first massive galaxy clusters are just beginning to form.

    10
    The galaxy cluster Abell 370, shown here, was one of the six massive galaxy clusters imaged in the Hubble Frontier Fields program. Since other great observatories were also used to image this region of sky, thousands of ultra-distant galaxies were revealed. By observing them again with a new scientific goal, Hubble’s BUFFALO (Beyond Ultra-deep Frontier Fields And Legacy Observations) program will obtain distances to these galaxies, enabling us to better understand how galaxies formed, evolved, and grew up in our Universe. When combined with intracluster light measurements, we could gain an even greater understanding, via multiple lines of evidence of the same structure, of the dark matter inside. (NASA, ESA, A. KOEKEMOER (STSCI), M. JAUZAC (DURHAM UNIVERSITY), C. STEINHARDT (NIELS BOHR INSTITUTE), AND THE BUFFALO TEAM)

    5.) Stellar era. Once the dark ages are over, the Universe is now transparent to starlight. The great recesses of the cosmos are now accessible, with stars, star clusters, galaxies, galaxy clusters, and the great, growing cosmic web all waiting to be discovered. The Universe is dominated, energy-wise, by dark matter and normal matter, and the gravitationally bound structures continue to grow larger and larger.

    The star-formation rate rises and rises, peaking about 3 billion years after the Big Bang. At this point, new galaxies continue to form, existing galaxies continue to grow and merge, and galaxy clusters attract more and more matter into them. But the amount of free gas within galaxies begins to drop, as the enormous amounts of star-formation have used up a large amount of it. Slowly but steadily, the star-formation rate drops.

    As time goes forward, the stellar death rate will outpace the birth rate, a fact made worse by the following surprise: as the matter density drops with the expanding Universe, a new form of energy — dark energy — begins to appear and dominate. 7.8 billion years after the Big Bang, distant galaxies stop slowing down in their recession from one another, and begin speeding up again. The accelerating Universe is upon us. A little bit later, 9.2 billion years after the Big Bang, dark energy becomes the dominant component of energy in the Universe. At this point, we enter the final era.

    10
    The different possible fates of the Universe, with our actual, accelerating fate shown at the right. After enough time goes by, the acceleration will leave every bound galactic or supergalactic structure completely isolated in the Universe, as all the other structures accelerate irrevocably away. We can only look to the past to infer dark energy’s presence and properties, which require at least one constant, but its implications are larger for the future.(NASA & ESA)

    6.) Dark Energy age.

    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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    DES is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

    Once dark energy takes over, something bizarre happens: the large-scale structure in the Universe ceases to grow. The objects that were gravitationally bound to one another before dark energy’s takeover will remain bound, but those that were not yet bound by the onset of the dark energy age will never become bound. Instead, they will simply accelerate away from one another, leading lonely existences in the great expanse of nothingness.

    The individual bound structures, like galaxies and groups/clusters of galaxies, will eventually merge to form one giant elliptical galaxy. The existing stars will die; new star formation will slow down to a trickle and then stop; gravitational interactions will eject most of the stars into the intergalactic abyss. Planets will spiral into their parent stars or stellar remnants, owing to decay by gravitational radiation. Even black holes, with extraordinarily long lifetimes, will eventually decay from Hawking radiation.

    In the end, only black dwarf stars and isolated masses too small to ignite nuclear fusion will remain, sparsely populated and disconnected from one another in this empty, ever-expanding cosmos. These final-state corpses will exist even googols of years onward, continuing to persist as dark energy remains the dominant factor in our Universe.

    This last era, of dark energy domination, has already begun. Dark energy became important for the Universe’s expansion 6 billion years ago, and began dominating the Universe’s energy content around the time our Sun and Solar System were being born. The Universe may have six unique stages, but for the entirety of Earth’s history, we’ve already been in the final one. Take a good look at the Universe around us. It will never be this rich — or this easy to access — ever again.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    “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 1:06 pm on July 30, 2019 Permalink | Reply
    Tags: "A Stellar Stream in the Milky Way Provides Evidence of Dark Substructure", , , , , , Dark Matter   

    From Harvard-Smithsonian Center for Astrophysics: “A Stellar Stream in the Milky Way Provides Evidence of Dark Substructure” 

    Harvard Smithsonian Center for Astrophysics


    From Harvard-Smithsonian Center for Astrophysics

    July 29, 2019
    Amy Oliver, Public Affairs Officer
    amy.oliver@cfa.harvard.edu
    +1-520-879-4406
    mobile: +1-801-783-9067

    1
    The colors of the stars in this GD-1 stellar stream model overlaid on a Gaia flux map show how the star’s orbits were affected by the impact of the unknown dark substructure with white representing a large difference and dark red representing almost no difference. The stream’s orbit is overplotted in the foreground. Ana Bonaca, ESA, Gaia.

    Scientists at the Center for Astrophysics | Harvard & Smithsonian have observed what may be evidence of dark matter interfering with a stellar stream in the Milky Way galaxy.

    For scientists and non-scientists alike, the discovery tells an exciting, edge-of-your-seat story. “We know that 90% of the mass in our universe is invisible. We don’t know what it is, but we’re curious,” said Dr. Ana Bonaca, ITC Fellow at the CfA and lead author of the study. “Stellar streams, which are what we’re studying here, tell us the story of our galaxy. They are so long and thin that they are sensitive to the tiniest disturbances as they orbit through the galaxy. Our findings are that…in action.”

    Gaia, a mission of the European Space Agency (ESA), had a second data release in April 2018, which provided the basis for a new study of GD-1, the longest and most visible thin stellar stream in the Milky Way.

    ESA/GAIA satellite

    Typically, stars are distributed close to uniformly along such streams, so scientists immediately noticed that some of the stars in the GD-1 stream were not behaving as expected.

    “Stellar streams were thought to be more or less smooth in appearance, but GD-1 has gaps or regions of lower density along the stream. Close to one of these gaps there is an offshoot of misaligned stars,” said Adrian Price-Whelan, a coauthor of the study. “So first, we found something interesting that didn’t match what we expected to see, thanks to Gaia.”

    Stellar streams are associations of stars that once previously belonged to a dwarf galaxy or a globular cluster, but that were pulled out by the Milky Way’s tidal forces and stretched out into streams. In the standard picture, these streams are long, thin, and regular. The observed behavior in GD-1, however, could not be explained by tidal forces alone. Instead, Bonaca and collaborators used numerical simulations to show that the observed gap and spur features could be the result of the stream encountering a dense, massive object.

    “We considered a number of different objects as potential sources of perturbation, but none of them seemed to fit. We looked at the orbits of all known satellites in the Galaxy, but none crossed paths with GD-1 recently. We also considered whether molecular clouds could have done the damage because GD-1 crosses the Milky Way disk, but found they are not dense enough,” said Bonaca. “There is no obvious culprit.”

    With no known culprits, scientists have turned to more exotic explanations, and that’s big news for dark matter theorists. “One of the fundamental predictions of the dark-matter model is that there ought to be many concentrations or clusters of dark matter orbiting in the outskirts of our Galaxy. This stream looks like it can be used to find those small clumps of dark matter,” said David Hogg, a coauthor of the study. “Ruling out all other possibilities and actually detecting a small clump of dark matter would be a huge clue for understanding the nature of this important component of the Universe.”

    While Gaia data was used to make initial observations, the team has since conducted follow-up observations with Hectochelle—a multi-object echelle spectrograph—at the MMT Observatory, located at the Fred Lawrence Whipple Observatory at Mt. Hopkins in Arizona.


    CfA U Arizona Fred Lawrence Whipple Observatory Steward Observatory MMT Telescope at the summit of Mount Hopkins near Tucson, Arizona, USA, Altitude 2,616 m (8,583 ft)

    CfA Whipple Observatory, located near Amado, Arizona on the slopes of Mount Hopkins, Altitude 2,606 m (8,550 ft)

    These new data will help in locating the dark substructure. In addition, Bonaca and other scientists have begun observing other stellar streams with unusual features.

    “When something passes close to a stellar stream, it leaves evidence behind, and we can see that something happened there. Even if it’s dark matter. Even if it’s invisible,” said Bonaca. “And if it is a clump of dark matter, there should be many of them. So we’re setting out to search for such oddities in other streams to find out for sure.”

    The results of the study are published in The Astrophysical Journal. In addition to Bonaca, the team consisted of CfA scientist Charlie Conroy; David W. Hogg representing the Centers for Cosmology and Particle Physics and for Data Science at New York University, Max-Planck-Institut fur Astronomie, and Flatiron Institute; and Adrian M. Price-Whelan at Princeton University and the Flatiron Institute.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    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 10:33 am on July 29, 2019 Permalink | Reply
    Tags: Dark Matter, SABRE (Sodium-iodide with Active Background Rejection), , ,   

    From Swinburne University and University of Melbourne: “Swinburne goes underground in search for dark matter” 

    Swinburne U bloc

    From Swinburne University

    and

    u-melbourne-bloc

    University of Melbourne

    29 July 2019

    Swinburne
    Media enquiries
    0455 502 999
    media@swinburne.edu.au

    Melbourne Media contact
    Emma Sun
    emma.sun@unimelb.edu.au
    +61 466 133 480

    1
    Swinburne Associate Professor Alan Duffy (left) at the site of the future Stawell Underground Physics Laboratory, where Minister for Regional Development Jaclyn Symes (centre) announced the funding.

    Swinburne University of Technology will be a key institution in the international project to explore and search for dark matter, following an announcement that Victoria’s state government will contribute $5 million to build the Stawell Underground Physics Laboratory.

    The funding has been announced by Victoria’s state Minister for Regional Development, Jaclyn Symes, and matches the federal government’s funding commitment confirmed in April.

    The laboratory will be built one kilometre underground, within the Stawell Gold Mine, as a bespoke excavated cavity 30 metres long, 10 metres wide and 10 metres high. It will provide ultra-low background research facilities (free from the particles that form background radiation) needed in the ground-breaking search for dark matter.

    Swinburne is one of six international institutes involved in the project, led by the University of Melbourne.

    The search for dark matter

    Swinburne astrophysicist, Associate Professor Alan Duffy, says understanding dark matter is one of the greatest scientific challenges of this century.

    “Astronomers have seen the movement of stars pulled by the gravity of an unseen companion. We now think that this unseen companion, dark matter, makes up five times more of the Universe than everything we can see combined,” he says.

    “The attention of the world’s physicists will now be on regional Victoria as a leader in the search for dark matter.”

    Associate Professor Duffy says that the establishment of Stawell as a physics research hub will also provide local education benefits.

    “This Lab will undoubtedly inspire local students to study physics in school and at university, but it also means that if they want to be part of a global scientific experiment, they can do that right here in Stawell.”

    The project is expected to deliver economic value to the region of $180.2 million in its first ten years, and support ongoing jobs.

    Ms Symes says: “With nearly 80 ongoing jobs connected to the Lab, this project will diversify Stawell’s economy – attracting a new highly-skilled workforce to the region to live and work.”

    University of Melbourne project leader, Professor Elisabetta Barberio, says the laboratory will be home to important scientific experiments.

    “The investment by both the state and federal governments ensure the Lab is large enough to host dark matter experiments as well as everything from fundamental cancer research into how radiation affects cells growing, to creating new ultra-sensitive detectors and novel geological exploration techniques,” she says.

    The project is a collaboration between six international partners. It will be led by the University of Melbourne alongside Swinburne, the University of Adelaide, the Australian National University, the Australian Nuclear Science and Technology Organisation (ANSTO) and the Italian National Institute for Nuclear Physics.

    The Southern Hemisphere’s first dark matter detector

    Swinburne is heavily involved in building the largest experiment to take place in the Stawell Underground Physics Laboratory – SABRE (Sodium-iodide with Active Background Rejection), which is the Southern Hemisphere’s first dark matter detector.

    The vessel will be arriving at Swinburne’s Wantirna campus in August, where it will undergo a rigorous assembly and electronics fit-out process, including leak testing and internal reflective surface coating. Only once the international team is satisfied that it meets the exacting standards for this kind of precision experiment will it move to the underground laboratory where the search for dark matter can begin.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    University of Melbourne

    Swinburne U Campus

    Swinburne is a large and culturally diverse organisation. A desire to innovate and bring about positive change motivates our students and staff. The result is in an institution that grows and evolves each year.

     
  • richardmitnick 7:53 am on July 26, 2019 Permalink | Reply
    Tags: , , , , , Dark Matter, Dark Stars,   

    From Astronomy Magazine- “Dark stars: The seeds of supermassive black holes?” 

    Astronomy magazine

    From Astronomy Magazine

    July 19, 2019
    Jake Parks

    The early universe was a very different place than it is now. But it may have been the perfect environment for a strange class of giant, puffy stars that used dark matter as fuel.

    1
    Dark matter annihilations may have fueled some of the universe’s first stars, allowing them to grow into giant, puffy clouds that are millions of times the mass and billions of times the brightness of the Sun. Astronomy: Roen Kelly after NSF.

    Powered by dark matter, dark stars are hypothetical objects that may have inhabited the early universe. If they existed, these mysterious beasts would not only have been the first stars to form in the cosmos, they also might explain how supermassive black holes got their start.

    Fueled by dark matter

    2
    Astronomy: Roen Kelly

    Normal stars all power themselves in the same way: nuclear fusion. Stars are so massive that they’re constantly on the verge of collapsing in on themselves. But as gravity squeezes a star, it generates so much heat in the star’s core that it smooshes the atoms together, releasing energy. This energy provides just enough outward pressure to precisely counterbalance a star’s gravitational collapse.

    But for dark stars, the story’s a little different.

    Theories suggest that dark stars would be mostly made from the same material as normal stars — namely, hydrogen and helium. But because these hypothetical dark stars would have formed in the early universe, when the cosmos was a lot denser, they also likely contain a small but significant amount of dark matter in the form of Weakly Interacting Massive Particles (WIMPs) — a leading dark matter candidate.

    These WIMPs are thought to serve as their own antimatter particles, they can annihilate with one another, producing pure energy. Within a dark star, these extremely powerful WIMP annihilations could offer enough outward pressure to prevent the star’s collapse without the need for core fusion.

    According to dark star researcher Katherine Freese, the Kodosky Endowed Chair of Physics at UT-Austin, WIMPs only make up about 0.1 percent of a dark star’s total mass. But just this tiny bit of WIMP fuel could keep a dark star chugging along for millions or even billions of years.

    3
    Astronomy: Roen Kelly

    What did dark stars look like?

    Dark stars don’t just behave differently than normal stars. They also look different.

    Because dark stars don’t rely on core fusion to stave off gravitational collapse, they’re not extremely compressed like normal stars. Instead, dark stars are likely giant, puffy clouds that shine extremely bright. Due to their bloated nature, Freese says, dark stars could even reach diameters of up to about 10 astronomical units (AU), where 1 AU is the average Earth-Sun distance of 93 million miles (150 million kilometers).

    4
    Astronomy: Roen Kelly

    “They can keep growing as long as there is dark matter fuel,” Freese told Astronomy. “We’ve assumed they can get up to 10 million times the mass of the Sun and 10 billion times as bright as the Sun, but we don’t really know. There is no cutoff in principle.”

    Searching for dark stars

    One of the hurdles to proving dark stars truly exist, though, is that these ironically bright objects depend on dark-matter annihilations to survive. However, such annihilations primarily occurred in the very early universe, when dark-matter particles were sharing close quarters. So, in order to spot ancient dark stars, we need telescopes capable of peering back to the extremely distant past.

    Fortunately, according to Freese, the upcoming James Webb Space Telescope should be able to spot dark stars — as long as we know what to look for.

    NASA/ESA/CSA Webb Telescope annotated

    “They would look completely different from hot stars,” Freese told Astronomy. “Dark stars are cool [17,500 °F (9,700 °C)]. So, they would look more like the Sun in terms of frequency of light, even though they’re much brighter. That combination of cool and bright is hard to explain with other objects.”

    “It is an exciting prospect that an entirely new type of star may be discovered in these upcoming data,” Freese and her colleagues wrote in a review paper.

    Seeding supermassive black holes

    If researchers are able to uncover evidence for the existence of dark stars, it would change how we think about the early stages of the universe. Darks stars would swiftly become the top candidates for the first generation of stars, which formed some 200 million years after the Big Bang.

    But dark stars might also explain one of the most nagging questions in cosmology: How did supermassive black holes first form?

    “If a dark star of a million solar masses were found [by James Webb] from very early on, it’s pretty clear that such an object would end up as a big black hole,” Freese says. “Then these could merge together to make supermassive black holes. A very reasonable scenario!”

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

     
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