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  • richardmitnick 7:02 am on September 9, 2014 Permalink | Reply
    Tags: , , , , , Royal Astronomical Society   

    From The Royal Astronomical Society: “Interactive dark matter could explain Milky Way’s missing satellite galaxies” 

    Royal Astronomical Society

    Royal Astronomical Society

    Tuesday, 09 September 2014
    Media contacts

    Durham University Media Relations Team
    Tel: +44 (0)191 334 6075
    media.relations@durham.ac.uk

    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7734 3307 x214
    Mob: +44 (0)794 124 8035
    rm@ras.org.uk

    Science contacts

    All the contacts are available for interview on Monday 8 and Tuesday 9 September.

    Professor Carlton Baugh
    Institute for Computational Cosmology
    Durham University
    Tel: +44 (0)191 33 43542
    c.m.baugh@durham.ac.uk

    Ryan Wilkinson
    Institute for Computational Cosmology
    Durham University
    Tel: +44 (0)191 33 45753
    ryan.wilkinson@durham.ac.uk

    Jascha Schewtschenko
    Institute for Computational Cosmology
    Durham University
    Tel: +44 (0)191 33 43710
    j.a.schewtschenko@durham.ac.uk

    Scientists believe they have found a way to explain why there are not as many galaxies orbiting the Milky Way as expected. Computer simulations of the formation of our galaxy suggest that there should be many more small galaxies around the Milky Way than are observed through telescopes.

    This has thrown doubt on the generally accepted theory of cold dark matter, an invisible and mysterious substance that scientists predict should allow for more galaxy formation around the Milky Way than is seen.

    sim
    The simulated distribution of dark matter in a Milky Way-like galaxy for standard, non-interacting dark matter (top left), warm dark matter (top right) and the new dark matter model that interacts with the photon background (bottom). Smaller structures are erased up to the point where, in the most extreme model (bottom right), the galaxy is completely sterilised. Credit: Durham University. Now cosmologists and particle physicists at the Institute for Computational Cosmology and the Institute for Particle Physics Phenomenology, at Durham University, working with colleagues at LAPTh College & University in France, think they have found a potential solution to the problem.

    Writing in the journal Monthly Notices of the Royal Astronomical Society, the scientists suggest that dark matter particles, as well as feeling the force of gravity, could have interacted with photons and neutrinos in the young Universe, causing the dark matter to scatter.

    Scientists think clumps of dark matter – or haloes – that emerged from the early Universe, trapped the intergalactic gas needed to form stars and galaxies. Scattering the dark matter particles wipes out the structures that can trap gas, stopping more galaxies from forming around the Milky Way and reducing the number that should exist.

    Lead author Dr Celine Boehm, in the Institute for Particle Physics Phenomenology at Durham University, said: “We don’t know how strong these interactions should be, so this is where our simulations come in.”

    “By tuning the strength of the scattering of particles, we change the number of small galaxies, which lets us learn more about the physics of dark matter and how it might interact with other particles in the Universe.”

    “This is an example of how a cosmological measurement, in this case the number of galaxies orbiting the Milky Way, is affected by the microscopic scales of particle physics.”

    There are several theories about why there are not more galaxies orbiting the Milky Way, which include the idea that heat from the Universe’s first stars sterilised the gas needed to form stars. The researchers say their current findings offer an alternative theory and could provide a novel technique to probe interactions between other particles and cold dark matter.

    two
    Two models of the dark matter distribution in the halo of a galaxy like the Milky Way, separated by the white line. The colours represent the density of dark matter, with red indicating high-density and blue indicating low-density. On the left is a simulation of how non-interacting cold dark matter produces an abundance of smaller satellite galaxies. On the right the simulation shows the situation when the interaction of dark matter with other particles reduces the number of satellite galaxies we expect to observe around the Milky Way. Credit: Durham University.

    Co-author Professor Carlton Baugh said: “Astronomers have long since reached the conclusion that most of the matter in the Universe consists of elementary particles known as dark matter.”

    “This model can explain how most of the Universe looks, except in our own backyard where it fails miserably.”

    “The model predicts that there should be many more small satellite galaxies around our Milky Way than we can observe.”

    “However, by using computer simulations to allow the dark matter to become a little more interactive with the rest of the material in the Universe, such as photons, we can give our cosmic neighbourhood a makeover and we see a remarkable reduction in the number of galaxies around us compared with what we originally thought.”

    The calculations were carried out using the COSMA supercomputer at Durham University, which is part of the UK-wide DiRAC super-computing framework.

    The work was funded by the Science and Technology Facilities Council and the European Union.

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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  • richardmitnick 6:14 pm on August 12, 2014 Permalink | Reply
    Tags: , , , , Royal Astronomical Society,   

    From The Royal Astronomical Society: “NASA’s NuSTAR sees rare blurring of black hole light” 

    Royal Astronomical Society

    Royal Astronomical Society

    12 August 2014
    J.D. Harrington
    Headquarters, Washington
    202-358-5241
    j.d.harrington@nasa.gov

    Whitney Clavin
    Jet Propulsion Laboratory
    Pasadena
    California
    United States
    Tel: +1 818 354 4673
    whitney.clavin@jpl.nasa.gov

    Science contact

    Prof Michael Parker
    Institute of Astronomy
    Cambridge
    United Kingdom
    Tel: +44 (0)1223 337 511
    mlparker@ast.cam.ac.uk

    Scientists have used NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), an orbiting X-ray telescope, to capture an extreme and rare event in the regions immediately surrounding a supermassive black hole. A compact source of X-rays that sits near the black hole, called the corona, has moved closer to the black hole over a period of just days. The researchers publish their results in Monthly Notices of the Royal Astronomical Society.

    NASA NuSTAR
    NASA/NuSTAR

    smbh
    An artist’s impression of a supermassive black hole and its surroundings. The regions around supermassive black holes shine brightly in X-rays. Some of this radiation comes from a surrounding disk, and most comes from the corona, pictured here as the white light at the base of a jet. This is one possible configuration for the Mrk 335 corona, as its actual shape is unclear. Credit: NASA-JPL / Caltech.

    “The corona recently collapsed in towards the black hole, with the result that the black hole’s intense gravity pulled all the light down onto its surrounding disk, where material is spiralling inward,” said Michael Parker of the Institute of Astronomy in Cambridge, lead author of the new paper.

    As the corona shifted closer to the black hole, the black hole’s gravitational field exerted a stronger tug on the x-rays emitted by the corona. The result was an extreme blurring and stretching of the X-ray light. Such events had been observed previously, but never to this degree and in such detail.

    Supermassive black holes are thought to reside in the centres of all galaxies. Some are more massive and rotate faster than others. The black hole in this new study, referred to as Markarian 335, or Mrk 335, is about 324 million light-years from Earth in the direction of the Pegasus constellation. It is one of the most extreme systems of which the mass and spin rate have ever been measured. The black hole squeezes about 10 million times the mass of our Sun into a region only 30 times as wide as the Sun’s diameter, and it spins so rapidly that space and time are dragged around with it.

    Even though some light falls into a supermassive black hole never to be seen again, other high-energy light emanates from both the corona and the surrounding accretion disk of superheated material. Though astronomers are uncertain of the shape and temperature of coronas, they know that they contain particles that move close to the speed of light.

    NASA’s Swift satellite has monitored Mrk 335 for years, and recently noted a dramatic change in its X-ray brightness. In what is called a ‘target-of-opportunity’ observation, NuSTAR was redirected to take a look at high-energy X-rays from this source in the range of 3 to 79 kiloelectron volts. This particular energy range offers astronomers a detailed look at what is happening near the event horizon, the region around a black hole from which light can no longer escape gravity’s grasp.

    NASA SWIFT Telescope
    NASA/SWIFT

    Follow-up observations indicate that the corona still is in this close configuration, months after it moved. Researchers don’t know whether and when the corona will shift back. What is more, the NuSTAR observations reveal that the grip of the black hole’s gravity pulled the corona’s light onto the inner portion of its superheated disk, better illuminating it. The shifting corona lit up the precise region they wanted to study, almost as if somebody had shone a flashlight for the astronomers.

    The new data could ultimately help determine more about the mysterious nature of black hole coronas. In addition, the observations have provided better measurements of Mrk 335’s furious relativistic spin rate. Relativistic speeds are those approaching the speed of light, as described by Albert Einstein’s theory of relativity.

    “We still don’t understand exactly how the corona is produced or why it changes its shape, but we see it lighting up material around the black hole, enabling us to study the regions so close in that effects described by Einstein’s theory of general relativity become prominent,” said NuSTAR Principal Investigator Fiona Harrison of the California Institute of Technology (Caltech) in Pasadena. “NuSTAR’s unprecedented capability for observing this and similar events allows us to study the most extreme light-bending effects of general relativity.”

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

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  • richardmitnick 8:35 am on August 8, 2014 Permalink | Reply
    Tags: , , , , Royal Astronomical Society,   

    From Royal Astronomical Society: “White dwarfs crashing into neutron stars explain the loneliest supernovae “ 

    Royal Astronomical Society

    Royal Astronomical Society

    08 August 2014
    Tom Frew
    International Press Officer
    University of Warwick
    Tel: +44 (0)24 765 75910
    a.t.frew@warwick.ac.uk

    Dr Robert Massey
    Royal Astronomical Society
    Tel: +44 (0)20 7734 3307 / 4582
    Mob: +44 (0)794 124 8035
    rm@ras.org.uk

    Science contact

    Dr Joseph Lyman
    Department of Physics
    University of Warwick
    J.D.Lyman@warwick.ac.uk

    A research team led by astronomers and astrophysicists at the University of Warwick have found that some of the Universe’s loneliest supernovae are likely created by the collisions of white dwarf stars into neutron stars. Dr Joseph Lyman from the University of Warwick is the lead researcher on the paper, which is published in the journal Monthly Notices of the Royal Astronomical Society.

    syar
    An artist’s illustration of a white dwarf star (the stretched object right of centre) being dragged on to a neutron star (bottom centre). At the top left is the galaxy where the pair originated and other more distant galaxies can be seen elsewhere in the image. Credit: (c) Mark A. Garlick / space-art.co.uk / University of Warwick.

    Previous studies had shown that calcium comprised up to half of the material thrown off in such explosions compared to only a tiny fraction in normal supernovae. This means that these curious events may actually be the dominant producers of calcium in our universe.

    “One of the weirdest aspects is that they seem to explode in unusual places. For example, if you look at a galaxy, you expect any explosions to roughly be in line with the underlying light you see from that galaxy, since that is where the stars are” comments Dr Lyman. “However, a large fraction of these are exploding at huge distances from their galaxies, where the number of stellar systems is miniscule.

    “What we address in the paper is whether there are any systems underneath where these transients have exploded, for example there could be very faint dwarf galaxies there, explaining the weird locations. We present observations, going just about as faint as you can go, to show there is in fact nothing at the location of these transients – so the question becomes, how did they get there?”

    Calcium-rich transients observed to date can be seen tens of thousands of parsecs away from any potential host galaxy, with a third of these events at least 65 thousand light years from a potential host galaxy.

    The researchers used the Very Large Telescope in Chile and Hubble Space Telescope observations of the nearest examples of these calcium rich transients to attempt to detect anything left behind or in the surrounding area of the explosion.

    ESO VLT Interferometer
    ESO/VLT

    NASA Hubble Telescope
    NASA/ESA Hubble Telescope

    The deep observations taken allowed them to rule out the presence of faint dwarf galaxies or globular star clusters at the locations of these nearest examples. Furthermore, an explanation for core-collapse supernovae, which calcium-rich transients resemble, although fainter, is the collapse of a massive star in a binary system where material is stripped from the massive star undergoing collapse. The researchers found no evidence for a surviving binary companion or other massive stars in the vicinity, allowing them to reject massive stars as the progenitors of calcium rich transients.

    Professor Andrew Levan from the University of Warwick’s Department of Physics and a researcher on the paper said: “It was increasingly looking like hypervelocity massive stars could not explain the locations of these supernovae. They must be lower mass longer lived stars, but still in some sort of binary systems as there is no known way that a single low mass star can go supernova by itself, or create an event that would look like a supernova.”

    The researchers then compared their data to what is known about short-duration gamma ray bursts (SGRBs). These are also often seen to explode in remote locations with no coincident galaxy detected. SGRBs are understood to occur when two neutron stars collide, or when a neutron star merges with a black hole – this has been backed up by the detection of a ‘kilonova‘ accompanying a SGRB thanks to work led by Professor Nial Tanvir, a collaborator on this study.

    Although neutron star and black hole mergers would not explain these brighter calcium rich transients, the research team considered that if the collision was instead between a white dwarf star and neutron star, it would fit their observations and analysis because:

    It would provide enough energy to generate the luminosity of calcium rich transients.
    The presence of a white dwarf would provide a mechanism to produce calcium rich material.
    The presence of the Neutron star could explain why this binary star system was found so far from a host galaxy.

    Dr Lyman said: “What we therefore propose is these are systems that have been ejected from their galaxy. A good candidate in this scenario is a white dwarf and a neutron star in a binary system. The neutron star is formed when a massive star goes supernova. The supernova explosion causes the neutron star to be ‘kicked’ to very high velocities (100s of km/s). This high velocity system can then escape its galaxy, and if the binary system survives the kick, the white dwarf and neutron star will later merge, causing the explosive transient.”

    The researchers note that such merging systems of white dwarfs and neutron stars are postulated to produce high energy gamma-ray bursts, motivating further observations of any new examples of calcium rich transients to confirm this. Additionally, such merging systems will contribute significant sources of gravitational waves, potentially detectable by upcoming experiments that will shed further light on the nature of these exotic systems.

    See the full article here.

    The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

    ScienceSprings relies on technology from

    MAINGEAR computers

    Lenovo
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    Dell
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