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  • richardmitnick 3:43 pm on December 27, 2017 Permalink | Reply
    Tags: , , , , , , Dark Matter Halo, , , Toothbrush Cluster   

    From CfA: “The Toothbrush Cluster” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    1
    A multiwavelength false-color image of the “Toothbrush” cluster of galaxies, 1RXS J0603.3+4214. The intensity in red shows the radio emission, blue is X -ray, and the background color composite is optical emission. Astronomers studying the cluster with new radio observations combined with other wavelengths have been able to confirm the galaxy merger scenario and estimate the magnetic field strength in the shocks. van Weeren et al.

    Most galaxies lie in clusters containing from a few to thousands of objects. Our Milky Way, for example, belongs to a cluster of about fifty galaxies called the Local Group whose other large member is the Andromeda galaxy about 2.3 million light-years away.

    Local Group. Andrew Z. Colvin 3 March 2011

    Andromeda Galaxy Adam Evans

    Clusters are the most massive gravitationally bound objects in the universe and form (according to current ideas) in a “bottoms-up” fashion with smaller structures developing first and larger groupings assembling later in cosmic history. Dark matter plays an important role in this growth process.

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

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

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

    Exactly how they grow, however, appears to depend on several competing physical processes including the behavior of the intracluster gas. There is more mass in this gas than there is in all the stars of a cluster’s galaxies, and the gas can have a temperature of ten million kelvin or even higher. As a result, the gas plays an important role in the cluster’s evolution. The hot intracluster gas contains rapidly moving charged particles that radiate strongly at radio wavelengths, sometimes revealing long filamentary structures.

    The “Toothbrush” galaxy cluster, 1RXS J0603.3+4214, hosts three of these radio structures as well as a large halo. The most prominent radio feature extends over more than six million light years, with three distinct components that resemble the brush and handle of a toothbrush. The handle is particularly enigmatic because, besides being large and very straight, it is off center from the axis of the cluster. The halo is thought to result from turbulence produced by the merger of galaxies, although some other possibilities have been suggested.

    CfA astronomers Reinout van Weeren, Bill Forman, Felipe Andrade-Santos, Ralph Kraft, and Christine Jones and their colleagues used the Very Large Array (VLA) facility to observe the relativistic particles in the cluster with precise, sensitive radio imaging, which they compared with Chandra X-ray and other datasets.

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    NASA/Chandra Telescope

    In the radio, the Toothbrush has a very narrow ridge, created by a huge shock resulting from the merger, and at least thirty-two previously undetected compact sources. The halo’s radio and X-ray morphologies are very similar and lend support to the merger scenario. Astronomers are also able to estimate the strength of the magnetic field, and combined with other results, use it to conclude that the merger scenario is most suitable.

    Reference(s):

    Deep VLA Observations of the Cluster 1RXS J0603.3+4214 in the Frequency Range 1-2 GHz, K. Rajpurohit, M. Hoeft, R. J. van Weeren, L. Rudnick, H. J. A. R ottgering, W. R. Forman, M. Bruggen, J. H. Croston, F. Andrade-Santos, W. A. Dawson, H. T. Intema, R. P. Kraft, C. Jones, and M. James Jee, http://lanl.arxiv.org/abs/1712.01327

    See the full article here .

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

     
  • richardmitnick 3:33 pm on December 6, 2017 Permalink | Reply
    Tags: , , , , , Dark Matter Halo, Dark matter provides the pull of gravity that causes the Universe to collapse into structures, , Massive Primordial Galaxies Found Swimming in Vast Ocean of Dark Matter, , , , With these exquisite ALMA observations astronomers are seeing the most massive galaxy known in the first billion years of the Universe in the process of assembling itself   

    From ALMA: “Massive Primordial Galaxies Found Swimming in Vast Ocean of Dark Matter” Revised to add contacts 

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    ALMA

    5 December, 2017

    Nicolás Lira
    Education and Public Outreach Coordinator
    Joint ALMA Observatory, Santiago – Chile
    Phone: +56 2 2467 6519
    Cell phone: +56 9 9445 7726
    Email: nicolas.lira@alma.cl

    Charles E. Blue
    Public Information Officer
    National Radio Astronomy Observatory Charlottesville, Virginia – USA
    Phone: +1 434 296 0314
    Cell phone: +1 202 236 6324
    Email: cblue@nrao.edu

    Richard Hook
    Public Information Officer, ESO
    Garching bei München, Germany
    Phone: +49 89 3200 6655
    Cell phone: +49 151 1537 3591
    Email: rhook@eso.org

    Masaaki Hiramatsu
    Education and Public Outreach Officer, NAOJ Chile
    Observatory
, Tokyo – Japan
    Phone: +81 422 34 3630
    Email: hiramatsu.masaaki@nao.ac.jp

    1
    Artist impression of a pair of galaxies from the very early Universe. Credit: NRAO/AUI/NSF; D. Berry

    Astronomers expect that the first galaxies, those that formed just a few hundred million years after the Big Bang, would share many similarities with some of the dwarf galaxies we see in the nearby Universe today. These early agglomerations of a few billion stars would then become the building blocks of the larger galaxies that came to dominate the Universe after the first few billion years.

    Ongoing observations with the Atacama Large Millimeter/submillimeter Array (ALMA), however, have discovered surprising examples of massive, star-filled galaxies seen when the Cosmos was less than a billion years old. This suggests that smaller galactic building blocks were able to assemble into large galaxies quite quickly.

    The latest ALMA observations push back this epoch of massive-galaxy formation even further by identifying two giant galaxies seen when the Universe was only 780 million years old, or about 5 percent its current age. ALMA also revealed that these uncommonly large galaxies are nestled inside an even-more-massive cosmic structure, a halo of dark matter with as much mass as several trillion suns.

    2
    To correct for the effects of gravitational lensing in these galaxies, the ALMA data (left panel) is compared to a lensing-distorted model image (second panel). The difference is shown in the third panel from the left. The structure of the galaxy, after removing the lensing effect, is shown at right. This image loops through the different velocity ranges within the galaxy, which appear at different frequencies to ALMA due to the Doppler effect. Credit: ALMA (ESO/NAOJ/NRAO); D. Marrone et al.

    The two galaxies are in such close proximity — less than the distance from the Earth to the center of our galaxy — that they will shortly merge to form the largest galaxy ever observed at that period in cosmic history. This discovery provides new details about the emergence of large galaxies and the role that dark matter plays in assembling the most massive structures in the Universe.

    The researchers report their findings in the journal Nature.

    “With these exquisite ALMA observations, astronomers are seeing the most massive galaxy known in the first billion years of the Universe in the process of assembling itself,” said Dan Marrone, associate professor of astronomy at the University of Arizona in Tucson and lead author on the paper.

    Astronomers are seeing these galaxies during a period of cosmic history known as the Epoch of Reionization when most of the intergalactic space was suffused with an obscuring fog of cold hydrogen gas.

    Reionization era and first stars, Caltech

    As more stars and galaxies formed, their energy eventually ionized the hydrogen between the galaxies, revealing the Universe as we see it today.

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

    “We usually view that as the time of little galaxies working hard to chew away at the neutral intergalactic medium,” said Marrone. “Mounting observational evidence with ALMA, however, has helped to reshape that story and continues to push back the time at which truly massive galaxies first emerged in the Universe.”

    The galaxies that Marrone and his team studied, collectively known as SPT0311-58, were originally identified as a single source by the National Science Foundation’s South Pole Telescope.

    South Pole Telescope SPTPOL. The SPT collaboration is made up of over a dozen (mostly North American) institutions, including the University of Chicago, the University of California, Berkeley, Case Western Reserve University, Harvard/Smithsonian Astrophysical Observatory, the University of Colorado Boulder, McGill University, The University of Illinois at Urbana-Champaign, University of California, Davis, Ludwig Maximilian University of Munich, Argonne National Laboratory, and the National Institute for Standards and Technology. It is funded by the National Science Foundation.

    These first observations indicated that this object was very distant and glowing brightly in infrared light, meaning that it was extremely dusty and likely going through a burst of star formation. Subsequent observations with ALMA revealed the distance and dual nature of the object, clearly resolving the pair of interacting galaxies.

    To make this observation, ALMA had some help from a gravitational lens, which provided an observing boost to the telescope.

    Gravitational Lensing NASA/ESA

    Gravitational lenses form when an intervening massive object, like a galaxy or galaxy cluster, bends the light from more distant galaxies. They do, however, distort the appearance of the object being studied, requiring sophisticated computer models to reconstruct the image as it would appear in its unaltered state.

    This “deconvolution” process provided intriguing details about the galaxies, showing that the larger of the two is forming stars at a rate of 2,900 solar masses per year. It also contains about 270 billion times the mass of our Sun in gas and nearly 3 billion times the mass of our Sun in dust. “That’s a whopping large quantity of dust, considering the young age of the system,” noted Justin Spilker, a recent graduate of the University of Arizona and now a postdoctoral fellow at the University of Texas at Austin.

    The astronomers determined that this galaxy’s rapid star formation was likely triggered by a close encounter with its slightly smaller companion, which already hosts about 35 billion solar masses of stars and is increasing its rate of starburst at the breakneck pace of 540 solar masses per year.

    The researchers note that galaxies of this era are messier than the ones we see in the nearby Universe. Their more jumbled shapes would be due to the vast stores of gas raining down on them and their ongoing interactions and mergers with their neighbors.

    The new observations also allowed the researchers to infer the presence of a truly massive dark matter halo surrounding both galaxies. Dark matter provides the pull of gravity that causes the Universe to collapse into structures (galaxies, groups, and clusters of galaxies, etc.).

    “If you want to see if a galaxy makes sense in our current understanding of cosmology, you want to look at the dark matter halo — the collapsed dark matter structure — in which it resides,” said Chris Hayward, an associate research scientist at the Center for Computational Astrophysics at the Flatiron Institute in New York City.

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

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

    “Fortunately, we know very well the ratio between dark matter and normal matter in the Universe, so we can estimate what the dark matter halo mass must be.”

    By comparing their calculations with current cosmological predictions, the researchers found that this halo is one of the most massive that should exist at that time.

    “There are more galaxies discovered with the South Pole Telescope that we’re following up, and there is a lot more survey data that we are just starting to analyze. Our hope is to find more objects like this, possibly even more distant ones, to better understand this population of extreme dusty galaxies and especially their relation to the bulk population of galaxies at this epoch,” said Joaquin Vieira of the University of Illinois at Urbana-Campaign.

    “In any case, our next round of ALMA observations should help us understand how quickly these galaxies came together and improve our understanding of massive galaxy formation during reionization,” added Marrone.

    Additional Information

    The research team was composed by D. P. Marrone[1], J. S. Spilker[1], C. C. Hayward[2,3], J. D. Vieira[4], M. Aravena[5], M. L. N. Ashby[3], M. B. Bayliss[6], M. Be ́thermin[7], M. Brodwin[8], M. S. Bothwell[9,10], J. E. Carlstrom[11,12,13,14], S. C. Chapman[15], Chian-Chou Chen[16], T. M. Crawford[11,14], D. J. M. Cunningham[15,17], C. De Breuck[16], C. D. Fassnacht[18], A. H. Gonzalez[19], T. R. Greve[20], Y. D. Hezaveh[21,28], K. Lacaille[22], K. C. Litke[1], S. Lower[4], J. Ma[19], M. Malkan[23], T. B. Miller[15], W. R. Morningstar[21], E. J. Murphy[24], D. Narayanan[19], K. A. Phadke[4], K. M. Rotermund[15], J. Sreevani[4], B. Stalder[25], A. A. Stark[3], M. L. Strandet[26,27], M. Tang[1], & A. Weiß[26].

    [1] Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA

    [2] Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA

    [3] Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

    [4] Department of Astronomy, University of Illinois, 1002 West Green St., Urbana, IL 61801

    [5] Nucleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile

    [6] Kavli Institute for Astrophysics & Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA

    [7] Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France

    [8] Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110, USA

    [9] Cavendish Laboratory, University of Cambridge, 19 J.J. Thomson Avenue, Cambridge, CB3 0HE, UK

    [10] Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

    [11] Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

    [12] Department of Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

    [13] Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

    [14] Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA

    [15] Dalhousie University, Halifax, Nova Scotia, Canada

    [16] European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany

    [17] Department of Astronomy and Physics, Saint Mary’s University, Halifax, Nova Scotia, Canada

    [18] Department of Physics, University of California, One Shields Avenue, Davis, CA 95616, USA

    [19] Department of Astronomy, University of Florida, Bryant Space Sciences Center, Gainesville, FL 32611 USA

    [20] Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

    [21] Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305, USA

    [22] Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 Canada

    [23] Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA

    [24] National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA

    [25] Large Synoptic Survey Telescope, 950 North Cherry Avenue, Tucson, AZ 85719, USA

    [26] Max-Planck-Institut fu ̈r Radioastronomie, Auf dem Hu ̈gel 69 D-53121 Bonn, Germany

    [27] International Max Planck Research School (IMPRS) for Astronomy and Astrophysics, Universities of Bonn and Cologne

    [28] Hubble Fellow

    See the full article here .

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    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

    NRAO Small
    ESO 50 Large
    NAOJ

     
  • richardmitnick 12:55 pm on September 14, 2017 Permalink | Reply
    Tags: , , , , , Dark Matter Halo, Dark matter may have strong self-interactions, Physicists Offer Explanation for Diverse Galaxy Rotations, ,   

    From UC Riverside: “Physicists Offer Explanation for Diverse Galaxy Rotations” 

    UC Riverside bloc

    UC Riverside

    September 14, 2017
    Iqbal Pittalwala

    1
    Hai-Bo Yu is an assistant professor of theoretical particle physics and astrophysics at UC Riverside. Photo credit: I. Pittalwala, UC Riverside.

    Identical twins are similar to each other in many ways, but they have different experiences, friends, and lifestyles.

    This concept is played out on a cosmological scale by galaxies. Two galaxies that appear at first glance to be very similar and effectively identical can have inner regions rotating at very different rates – the galactic analog of twins with different lifestyles.

    A team of physicists, led by Hai-Bo Yu of the University of California, Riverside, has found a simple and viable explanation for this diversity.

    Every galaxy sits within a dark matter halo that forms the gravitational scaffolding holding it together.

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

    The distribution of dark matter in this halo can be inferred from the motion of stars and gas particles in the galaxy.

    Yu and colleagues report in Physical Review Letters that diverse galactic-rotation curves, a graph of rotation speeds at different distances from the center, can be naturally explained if dark matter particles are assumed to strongly collide with one another in the inner halo, close to the galaxy’s center – a process called dark matter self-interaction.

    “In the prevailing dark matter theory, called Cold Dark Matter or CDM, dark matter particles are assumed to be collisionless, aside from gravity,” said Yu, an assistant professor of theoretical particle physics and astrophysics, who led the research. “We invoke a different theory, the self-interacting dark matter model or SIDM, to show that dark matter self-interactions thermalize the inner halo, which ties ordinary matter and dark matter distributions together so that they behave like a collective unit. The self-interacting dark matter halo then becomes flexible enough to accommodate the observed diverse rotation curves.”

    Yu explained that the dark matter collisions take place in the dense inner halo, where the luminous galaxy is located. When the particles collide, they exchange energy and thermalize. For low-luminous galaxies, the thermalization process heats up the inner dark matter particles and pushes them out of the central region, reducing the density, analogous to a popcorn machine in which kernels hit each other as they pop, causing them to fly up from the bottom of the machine. For high-luminous galaxies such as the Milky Way, thermalization pulls the particles into the deep potential well of the luminous matter and increases the dark matter density. In addition, the cosmological assembly history of halos also plays a role in generating the observed diversity.

    “Our work demonstrates that dark matter may have strong self-interactions, a radical deviation from the prevailing theory,” Yu said. “It well explains the observed diversity of galactic rotating curves, while being consistent with other cosmological observations.”

    Dark matter makes up about 85 percent of matter in the universe, but its nature remains largely unknown despite its unmistakable gravitational imprint on astronomical and cosmological observations. The conventional way to study dark matter is to assume that it has some additional, nongravitational interaction with visible matter that can be studied in the lab. Physicists do not know, however, if such an interaction between dark and visible matter even exists.

    Over the last decade, Yu has pioneered a new line of research based on the following premise: Setting aside whether dark matter interacts with visible matter, what happens if dark matter interacts with itself through some new dark force?

    Yu posited the new dark force would affect the dark matter distribution in each galaxy’s halo. He realized that there is indeed a discrepancy between CDM and astronomical observations that could be solved if dark matter is self-interacting.

    “The compatibility of this hypothesis with observations is a major advance in the field,” said Flip Tanedo, an assistant professor of theoretical particle physics at UC Riverside, who was not involved in the research. “The SIDM paradigm is a bridge between fundamental particle physics and observational astronomy. The consistency with observations is a big hint that this proposal has a chance of being correct and lays the foundation for future observational, experimental, numerical, and theoretical work. In this way, it is paving the way to new interdisciplinary research.”

    SIDM was first proposed in 2000 by a pair of eminent astrophysicists. It experienced a revival in the particle physics community around 2009, aided in part by key work by Yu and collaborators.

    “This is a special time for this type of research because numerical simulations of galaxies are finally approaching a precision where they can make concrete predictions to compare the observational predictions of the self-interacting versus cold dark matter scenarios,” Tanedo said. “In this way, Hai-Bo is the architect of modern self-interacting dark matter and how it merges multiple different fields: theoretical high-energy physics, experimental high-energy physics, observational astronomy, numerical simulations of astrophysics, and early universe cosmology and galaxy formation.”

    The research paper is included by Physical Review Letters as a “Editor’s Suggestion” and featured also in APS Physics.

    Yu was joined in the research by Ayuki Kamada, a postdoctoral researcher at UCR; and UC Irvine’s Manoj Kaplinghat and Andrew B. Pace.

    Yu’s research was supported by grants from the U.S. Department of Energy and the Hellman Fellows Fund. The National Science Foundation provided the research team with additional funding.

    See the full article here .

    [This article would have been helped with examples of galaxies.

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    UC Riverside Campus

    The University of California, Riverside is one of 10 universities within the prestigious University of California system, and the only UC located in Inland Southern California.

    Widely recognized as one of the most ethnically diverse research universities in the nation, UCR’s current enrollment is more than 21,000 students, with a goal of 25,000 students by 2020. The campus is in the midst of a tremendous growth spurt with new and remodeled facilities coming on-line on a regular basis.

    We are located approximately 50 miles east of downtown Los Angeles. UCR is also within easy driving distance of dozens of major cultural and recreational sites, as well as desert, mountain and coastal destinations.

     
  • richardmitnick 12:46 pm on August 16, 2017 Permalink | Reply
    Tags: , As time passes and we still haven’t detected WIMPs, , , , Can Radio Telescopes Find Axions?, , Dark Matter Halo, Galactic halo model, Magnetic fields can change axions to and from photons, , ,   

    From AAS NOVA: “Can Radio Telescopes Find Axions?” 

    AASNOVA

    American Astronomical Society

    16 August 2017
    Susanna Kohler

    1
    A simulation showing the distribution of dark matter in the universe. [AMNH]

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

    In the search for dark matter, the most commonly accepted candidates are invisible, massive particles commonly referred to as WIMPs. But as time passes and we still haven’t detected WIMPs, alternative scenarios are becoming more and more appealing. Prime among these is the idea of axions.

    2
    The Italian PVLAS is an example of a laboratory experiment that attempted to confirm the existence of axions. [PVLAS]

    A Bizarre Particle

    Axions are a type of particle first proposed in the late 1970s. These theorized particles arose from a new symmetry introduced to solve ongoing problems with the standard model for particle physics, and they were initially predicted to have more than a keV in mass. For this reason, their existence was expected to be quickly confirmed by particle-detector experiments — yet no detections were made.

    Today, after many unsuccessful searches, experiments and theory tell us that if axions exist, their masses must lie between 10-6–10-3 eV. This is minuscule — an electron’s mass is around 500,000 eV, and even neutrinos are on the scale of a tenth of an eV!

    But enough of anything, even something very low-mass, can weigh a lot. If they are real, then axions were likely created in abundance during the Big Bang — and unlike heavier particles, they can’t decay into anything lighter, so we would expect them all to still be around today. Our universe could therefore be filled with invisible axions, potentially providing an explanation for dark matter in the form of many, many tiny particles.

    4
    Artist’s impression of the central core of proposed Square Kilometer Array antennas. [SKA/Swinburne Astronomy Productions]

    How Do We Find Them?

    Axions barely interact with ordinary matter and they have no electric charge. One of the few ways we can detect them is with magnetic fields: magnetic fields can change axions to and from photons.

    While many studies have focused on attempting to detect axions in laboratory experiments, astronomy provides an alternative: we can search for cosmological axions. Now scientists Katharine Kelley and Peter Quinn at ICRAR, University of Western Australia, have explored how we might use next-generation radio telescopes to search for photons that were created by axions interacting with the magnetic fields of our galaxy.

    5
    Potential axion coupling strengths vs. mass (click for a closer look). The axion mass is thought to lie between a µeV and a meV; two theoretical models are shown with dashed lines. The plot shows the sensitivity of the upcoming SKA and its precursors, ASKAP and MEERKAT. [Kelley&Quinn 2017]

    SKA/ASKAP radio telescope at the Murchison Radio-astronomy Observatory (MRO) in Mid West region of Western Australia

    SKA Meerkat telescope, 90 km outside the small Northern Cape town of Carnarvon, SA

    Hope for Next-Gen Telescopes

    By using a simple galactic halo model and reasonable assumptions for the central galactic magnetic field — even taking into account the time dependence of the field — Kelley and Quinn estimate the radio-frequency power density that we would observe at Earth from axions being converted to photons within the Milky Way’s magnetic field.

    The authors then compare this signature to the detection capabilities of upcoming radio telescope arrays. They show that the upcoming Square Kilometer Array and its precursors should have the capability to detect signs of axions across large parts of parameter space.

    Kelley and Quinn conclude that there’s good cause for optimism about future radio telescopes’ ability to detect axions. And if we did succeed in making a detection, it would be a triumph for both particle physics and astrophysics, finally providing an explanation for the universe’s dark matter.

    Citation

    Katharine Kelley and P. J. Quinn 2017 ApJL 845 L4. doi:10.3847/2041-8213/aa808d

    Related Journal Articles
    See the full article for further references with links.

    See the full article here .

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    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 4:20 pm on July 27, 2017 Permalink | Reply
    Tags: , , , , , Dark Matter Halo,   

    From CfA: “Mapping Dark Matter” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    July 21, 2017 [Not making it into social media, but I need the work.]

    1
    Abell 2744, a cluster of galaxies whose dark matter halo has imaged more distant galaxies as seen in this Hubble Space Telescope image. Astronomers have compared the image to simulations of dark matter lensing and found excellent agreement, indicating that that current models of dark matter behavior on the large scale are quite good. NASA/ESA/Hubble.

    About eighty-five percent of the matter in the universe is in the form of dark matter, whose nature remains a mystery. The rest of the matter in the universe is of the kind found in atoms. Astronomers studying the evolution of galaxies in the universe find that dark matter exhibits gravity and, because it is so abundant, it dominates the formation of large-scale structures in the universe like clusters of galaxies. Dark matter is hard to observe directly, needless to say, and it shows no evidence of interacting with itself or other matter other than via gravity, but fortunately it can be traced by modeling sensitive observations of the distributions of galaxies across a range of scales.

    Galaxies generally reside at the centers of vast clumps of dark matter called haloes because they surround the clusters of galaxies.

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

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

    Gravitational lensing of more distant galaxies by dark matter haloes offers a particularly unique and powerful probe of the detailed distribution of dark matter.

    So-called strong gravitational lensing creates highly distorted, magnified and occasionally multiple images of a single source; so-called weak lensing results in modestly yet systematically deformed shapes of background galaxies that can also provide robust constraints on the distribution of dark matter within the clusters.

    Gravitational Lensing NASA/ESA

    Weak gravitational lensing HST

    CfA astronomers Annalisa Pillepich and Lars Hernquist and their colleagues compared gravitationally distorted Hubble images of the galaxy cluster Abell 2744 and two other clusters with the results of computer simulations of dark matter haloes. They found, in agreement with key predictions in the conventional dark matter picture, that the detailed galaxy substructures depend on the dark matter halo distribution, and that the total mass and the light trace each other. They also found a few discrepancies: the radial distribution of the dark matter is different from that predicted by the simulations, and the effects of tidal stripping and friction in galaxies are smaller than expected, but they suggest these issues might be resolved with more precise simulations. Overall, however, the standard model of dark matter does an excellent and reassuring job of describing galaxy clustering.

    Science paper:
    Mapping Substructure in the HST Frontier Fields Cluster Lenses and in Cosmological Simulations MNRAS

    See the full article here .

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

     
  • richardmitnick 5:00 pm on June 13, 2017 Permalink | Reply
    Tags: A different kind of dark matter could help to resolve an old celestial conundrum, , , , , , Dark Matter Halo, Dark matter superfluid, Dark matter vortices, , Kent Ford, , ,   

    From Quanta: “Dark Matter Recipe Calls for One Part Superfluid” 

    Quanta Magazine
    Quanta Magazine

    June 13, 2017
    Jennifer Ouellette

    A different kind of dark matter could help to resolve an old celestial conundrum.

    1
    Markos Kay for Quanta Magazine

    For years, dark matter has been behaving badly. The term was first invoked nearly 80 years ago by the astronomer Fritz Zwicky, who realized that some unseen gravitational force was needed to stop individual galaxies from escaping giant galaxy clusters. Later, Vera Rubin and Kent Ford used unseen dark matter to explain why galaxies themselves don’t fly apart.

    Yet even though we use the term “dark matter” to describe these two situations, it’s not clear that the same kind of stuff is at work. The simplest and most popular model holds that dark matter is made of weakly interacting particles that move about slowly under the force of gravity. This so-called “cold” dark matter accurately describes large-scale structures like galaxy clusters. However, it doesn’t do a great job at predicting the rotation curves of individual galaxies. Dark matter seems to act differently at this scale.

    In the latest effort to resolve this conundrum, two physicists have proposed that dark matter is capable of changing phases at different size scales. Justin Khoury, a physicist at the University of Pennsylvania, and his former postdoc Lasha Berezhiani, who is now at Princeton University, say that in the cold, dense environment of the galactic halo, dark matter condenses into a superfluid — an exotic quantum state of matter that has zero viscosity. If dark matter forms a superfluid at the galactic scale, it could give rise to a new force that would account for the observations that don’t fit the cold dark matter model. Yet at the scale of galaxy clusters, the special conditions required for a superfluid state to form don’t exist; here, dark matter behaves like conventional cold dark matter.

    “It’s a neat idea,” said Tim Tait, a particle physicist at the University of California, Irvine. “You get to have two different kinds of dark matter described by one thing.” And that neat idea may soon be testable. Although other physicists have toyed with similar ideas, Khoury and Berezhiani are nearing the point where they can extract testable predictions that would allow astronomers to explore whether our galaxy is swimming in a superfluid sea.

    Impossible Superfluids

    Here on Earth, superfluids aren’t exactly commonplace. But physicists have been cooking them up in their labs since 1938. Cool down particles to sufficiently low temperatures and their quantum nature will start to emerge. Their matter waves will spread out and overlap with one other, eventually coordinating themselves to behave as if they were one big “superatom.” They will become coherent, much like the light particles in a laser all have the same energy and vibrate as one. These days even undergraduates create so-called Bose-Einstein condensates (BECs) in the lab, many of which can be classified as superfluids.

    Superfluids don’t exist in the everyday world — it’s too warm for the necessary quantum effects to hold sway. Because of that, “probably ten years ago, people would have balked at this idea and just said ‘this is impossible,’” said Tait. But recently, more physicists have warmed to the possibility of superfluid phases forming naturally in the extreme conditions of space. Superfluids may exist inside neutron stars, and some researchers have speculated that space-time itself may be a superfluid. So why shouldn’t dark matter have a superfluid phase, too?

    To make a superfluid out of a collection of particles, you need to do two things: Pack the particles together at very high densities and cool them down to extremely low temperatures. In the lab, physicists (or undergraduates) confine the particles in an electromagnetic trap, then zap them with lasers to remove the kinetic energy and lower the temperature to just above absolute zero.

    2
    Lucy Reading-Ikkanda/Quanta Magazine

    The dark matter particles that would make Khoury and Berezhiani’s idea work are emphatically not WIMP-like. WIMPs should be pretty massive as fundamental particles go — about as massive as 100 protons, give or take. For Khoury’s scenario to work, the dark matter particle would have to be a billion times less massive. Consequently, there should be billions of times as many of them zipping through the universe — enough to account for the observed effects of dark matter and to achieve the dense packing required for a superfluid to form. In addition, ordinary WIMPs don’t interact with one another. Dark matter superfluid particles would require strongly interacting particles.

    The closest candidate is the axion, a hypothetical ultralight particle with a mass that could be 10,000 trillion trillion times as small as the mass of the electron. According to Chanda Prescod-Weinstein, a theoretical physicist at the University of Washington, axions could theoretically condense into something like a Bose-Einstein condensate.

    But the standard axion doesn’t quite fit Khoury and Berezhiani’s needs. In their model, particles would need to experience a strong, repulsive interaction with one another. Typical axion models have interactions that are both weak and attractive. That said, “I think everyone thinks that dark matter probably does interact with itself at some level,” said Tait. It’s just a matter of determining whether that interaction is weak or strong.

    Cosmic Superfluid Searches

    The next step for Khoury and Berezhiani is to figure out how to test their model — to find a telltale signature that could distinguish this superfluid concept from ordinary cold dark matter. One possibility: dark matter vortices. In the lab, rotating superfluids give rise to swirling vortices that keep going without ever losing energy. Superfluid dark matter halos in a galaxy should rotate sufficiently fast to also produce arrays of vortices. If the vortices were massive enough, it would be possible to detect them directly.

    Inside galaxies, the role of the electromagnetic trap would be played by the galaxy’s gravitational pull, which could squeeze dark matter together enough to satisfy the density requirement. The temperature requirement is easier: Space, after all, is naturally cold.

    Outside of the “halos” found in the immediate vicinity of galaxies, the pull of gravity is weaker, and dark matter wouldn’t be packed together tightly enough to go into its superfluid state. It would act as dark matter ordinarily does, explaining what astronomers see at larger scales.

    But what’s so special about having dark matter be a superfluid? How can this special state change the way that dark matter appears to behave? A number of researchers over the years have played with similar ideas. But Khoury’s approach is unique because it shows how the superfluid could give rise to an extra force.

    In physics, if you disturb a field, you’ll often create a wave. Shake some electrons — for instance, in an antenna — and you’ll disturb an electric field and get radio waves. Wiggle the gravitational field with two colliding black holes and you’ll create gravitational waves. Likewise, if you poke a superfluid, you’ll produce phonons — sound waves in the superfluid itself. These phonons give rise to an extra force in addition to gravity, one that’s analogous to the electrostatic force between charged particles. “It’s nice because you have an additional force on top of gravity, but it really is intrinsically linked to dark matter,” said Khoury. “It’s a property of the dark matter medium that gives rise to this force.” The extra force would be enough to explain the puzzling behavior of dark matter inside galactic halos.

    A Different Dark Matter Particle

    Dark matter hunters have been at work for a long time. Their efforts have focused on so-called weakly interacting massive particles, or WIMPs. WIMPs have been popular because not only would the particles account for the majority of astrophysical observations, they pop out naturally from hypothesized extensions of the Standard Model of particle physics.

    Yet no one has ever seen a WIMP, and those hypothesized extensions of the Standard Model haven’t shown up in experiments either, much to physicists’ disappointment.

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

    With each new null result, the prospects dim even more, and physicists are increasingly considering other dark matter candidates. “At what point do we decide that we’ve been barking up the wrong tree?” said Stacy McGaugh, an astronomer at Case Western Reserve University.

    Unfortunately, this is unlikely to be the case: Khoury’s most recent computer simulations suggest that vortices in the dark matter superfluid would be “pretty flimsy,” he said, and unlikely to offer researchers clear-cut evidence that they exist. He speculates it might be possible to exploit the phenomenon of gravitational lensing to see if there are any scattering effects, similar to how a crystal will scatter X-ray light that passes through it.

    Gravitational Lensing NASA/ESA

    Astronomers could also search for indirect evidence that dark matter behaves like a superfluid. Here, they’d look to galactic mergers.

    The rate that galaxies collide with one another is influenced by something called dynamical friction. Imagine a massive body passing through a sea of particles. Many of the small particles will get pulled along by the massive body. And since the total momentum of the system can’t change, the massive body must slow down a bit to compensate.

    That’s what happens when two galaxies start to merge. If they get sufficiently close, their dark matter halos will start to pass through each other, and the rearrangement of the independently moving particles will give rise to dynamical friction, pulling the halos even closer. The effect helps galaxies to merge, and works to increase the rate of galactic mergers across the universe.

    But if the dark matter halo is in a superfluid phase, the particles move in sync. There would be no friction pulling the galaxies together, so it would be more difficult for them to merge. This should leave behind a telltale pattern: rippling interference patterns in how matter is distributed in the galaxies.

    Perfectly Reasonable Miracles

    While McGaugh is mostly positive about the notion of superfluid dark matter, he confesses to a niggling worry that in trying so hard to combine the best of both worlds, physicists might be creating what he terms a “Tycho Brahe solution.” The 16th-century Danish astronomer invented a hybrid cosmology in which the Earth was at the center of the universe but all the other planets orbited the sun. It attempted to split the difference between the ancient Ptolemaic system and the Copernican cosmology that would eventually replace it. “I worry a little that these kinds of efforts are in that vein, that maybe we’re missing something more fundamental,” said McGaugh. “But I still think we have to explore these ideas.”

    Tait admires this new superfluid model intellectually, but he would like to see the theory fleshed out more at the microscopic level, to a point where “we can really calculate everything and show why it all works out the way it’s supposed to. At some level, what we’re doing now is invoking a few miracles” in order to get everything to fit into place, he said. “Maybe they’re perfectly reasonable miracles, but I’m not fully convinced yet.”

    One potential sticking point is that Khoury and Berezhiani’s concept requires a very specific kind of particle that acts like a superfluid in just the right regime, because the kind of extra force produced in their model depends upon the specific properties of the superfluid. They are on the hunt for an existing superfluid — one created in the lab — with those desired properties. “If you could find such a system in nature, it would be amazing,” said Khoury, since this would essentially provide a useful analog for further exploration. “You could in principle simulate the properties of galaxies using cold atoms in the lab to mimic how superfluid dark matter behaves.”

    While researchers have been playing with superfluids for many decades, particle physicists are only just beginning to appreciate the usefulness of some of the ideas coming from subjects like condensed matter physics. Combining tools from those disciplines and applying it to gravitational physics might just resolve the longstanding dispute on dark matter — and who knows what other breakthroughs might await?

    “Do I need superfluid models? Physics isn’t really about what I need,” said Prescod-Weinstein. “It’s about what the universe may be doing. It may be naturally forming Bose-Einstein condensates, just like masers naturally form in the Orion nebula. Do I need lasers in space? No, but they’re pretty cool.”

    See the full article here .

    Please help promote STEM in your local schools.

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

     
  • richardmitnick 7:51 am on February 23, 2016 Permalink | Reply
    Tags: , , , Dark Matter Halo,   

    From NAOJ: “Formation and Evolution of Dark Matter Halos (II. Formation of the Large-Scale Structure of the Universe) 

    NAOJ

    NAOJ

    Dark matter halo
    Visualization of Dark Matter Halo.ESA

    This video is a visualization of the evolution of dark matter distribution from the beginning of the Universe up to the present. Right after the birth of the Universe, dark matter is distributed almost uniformly. But parts with slightly higher densities gravitationally attract the surrounding dark matter to form small halos. Through mergers, these small halos evolve into larger haloes. Within these larger halos gas collects and galaxies form. Furthermore, galaxies group together to form galaxy clusters connected by galaxies distributed in a framework pattern. This is known as the large-scale structure of the Universe.


    Download mp4 video here .

    Exploring the History of Structure Formation in the Universe through Large-Scale Simulations

    In this simulation, the dark matter density distribution at the beginning of the Universe is represented by approximately 8.6 billion particles. The evolution of dark matter halos through mutual gravitational interaction is followed up to the present. By calculating the evolution of the (baryonic) matter, which is the material for stars and galaxies, based on the dark matter distribution obtained through these calculations, it has become possible to predict the distribution, evolution, and statistical characteristics of things like galaxies or active galactic nuclei over a wider area than ever before. Simulation results obtained in this manner can be used as a database to compare with wide field observations performed in the future by facilities like the Subaru Telescope.

    See the full article here .

    Please help promote STEM in your local schools.

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    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

    NAOJ Subaru Telescope

    NAOJ Subaru Telescope interior
    Subaru

    ALMA Array
    ALMA

    sft
    Solar Flare Telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Observatory

    Nobeyama Solar Radio Telescope Array
    Nobeyama Radio Observatory: Solar

    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

     
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