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  • richardmitnick 9:28 pm on April 29, 2016 Permalink | Reply
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    From Fermi: “NASA’s Fermi Telescope Poised to Pin Down Gravitational Wave Sources” 

    NASA Fermi Banner

    NASA/Fermi Telescope
    NASA Fermi

    April 18, 2016
    By Francis Reddy
    NASA’s Goddard Space Flight Center, Greenbelt, Maryland

    On Sept. 14, waves of energy traveling for more than a billion years gently rattled space-time in the vicinity of Earth. The disturbance, produced by a pair of merging black holes, was captured by the Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana. This event marked the first-ever detection of gravitational waves and opens a new scientific window on how the universe works.

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

    Caltech/MIT Advanced aLIGO Hanford Washington USA installation
    Caltech/MIT Advanced aLIGO Hanford Washington USA installation

    Less than half a second later, the Gamma-ray Burst Monitor (GBM) on NASA’s Fermi Gamma-ray Space Telescope picked up a brief, weak burst of high-energy light consistent with the same part of the sky. Analysis of this burst suggests just a 0.2-percent chance of simply being random coincidence. Gamma-rays arising from a black hole merger would be a landmark finding because black holes are expected to merge “cleanly,” without producing any sort of light.


    Access mp4 video here .
    This visualization shows gravitational waves emitted by two black holes (black spheres) of nearly equal mass as they spiral together and merge. Yellow structures near the black holes illustrate the strong curvature of space-time in the region. Orange ripples represent distortions of space-time caused by the rapidly orbiting masses. These distortions spread out and weaken, ultimately becoming gravitational waves (purple). The merger timescale depends on the masses of the black holes. For a system containing black holes with about 30 times the sun’s mass, similar to the one detected by LIGO in 2015, the orbital period at the start of the movie is just 65 milliseconds, with the black holes moving at about 15 percent the speed of light. Space-time distortions radiate away orbital energy and cause the binary to contract quickly. As the two black holes near each other, they merge into a single black hole that settles into its “ringdown” phase, where the final gravitational waves are emitted. For the 2015 LIGO detection, these events played out in little more than a quarter of a second. This simulation was performed on the Pleiades supercomputer at NASA’s Ames Research Center. Credits: NASA/J. Bernard Kelly (Goddard), Chris Henze (Ames) and Tim Sandstrom (CSC Government Solutions LLC)

    “This is a tantalizing discovery with a low chance of being a false alarm, but before we can start rewriting the textbooks we’ll need to see more bursts associated with gravitational waves from black hole mergers,” said Valerie Connaughton, a GBM team member at the Universities Space Research Association’s Science and Technology Institute in Huntsville, Alabama, and lead author of a paper* on the burst now under review by The Astrophysical Journal.

    Detecting light from a gravitational wave source will enable a much deeper understanding of the event. Fermi’s GBM sees the entire sky not blocked by Earth and is sensitive to X-rays and gamma rays with energies between 8,000 and 40 million electron volts (eV). For comparison, the energy of visible light ranges between about 2 and 3 eV.

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    This image, taken in May 2008 as the Fermi Gamma-ray Space Telescope was being readied for launch, highlights the detectors of its Gamma-ray Burst Monitor (GBM). The GBM is an array of 14 crystal detectors. Credits: NASA/Jim Grossmann

    With its wide energy range and large field of view, the GBM is the premier instrument for detecting light from short gamma-ray bursts (GRBs), which last less than two seconds. They are widely thought to occur when orbiting compact objects, like neutron stars and black holes, spiral inward and crash together.

    Black holes merging Swinburne Astronomy Productions
    Black holes merging Swinburne Astronomy Productions

    These same systems also are suspected to be prime producers of gravitational waves.

    “With just one joint event, gamma rays and gravitational waves together will tell us exactly what causes a short GRB,” said Lindy Blackburn, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and a member of the LIGO Scientific Collaboration. “There is an incredible synergy between the two observations, with gamma rays revealing details about the source’s energetics and local environment and gravitational waves providing a unique probe of the dynamics leading up to the event.” He will be discussing the burst and how Fermi and LIGO are working together in an invited talk at the American Physical Society meeting in Salt Lake City on Tuesday.

    Currently, gravitational wave observatories possess relatively blurry vision. This will improve in time as more facilities begin operation, but for the September event, dubbed GW150914 after the date, LIGO scientists could only trace the source to an arc of sky spanning an area of about 600 square degrees, comparable to the angular area on Earth occupied by the United States.

    “That’s a pretty big haystack to search when your needle is a short GRB, which can be fast and faint, but that’s what our instrument is designed to do,” said co-author Eric Burns, a GBM team member and graduate student at the University of Alabama in Huntsville. “A GBM detection allows us to whittle down the LIGO area and substantially shrinks the haystack.”


    Access mp4 video here .
    Fermi’s GBM saw a fading X-ray flash at nearly the same moment LIGO detected gravitational waves from a black hole merger in 2015. This movie shows how scientists can narrow down the location of the LIGO source on the assumption that the burst is connected to it. In this case, the LIGO search area is reduced by two-thirds. Greater improvements are possible in future detections.
    Credits: NASA’s Goddard Space Flight Center

    Less than half a second after LIGO detected gravitational waves, the GBM picked up a faint pulse of high-energy X-rays lasting only about a second. The burst effectively occurred beneath Fermi and at a high angle to the GBM detectors, a situation that limited their ability to establish a precise position. Fortunately, Earth blocked a large swath of the burst’s likely location as seen by Fermi at the time, allowing scientists to further narrow down the burst’s position.

    The GBM team calculates less than a 0.2-percent chance random fluctuations would have occurred in such close proximity to the merger. Assuming the events are connected, the GBM localization and Fermi’s view of Earth combine to reduce the LIGO search area by about two-thirds, to 200 square degrees. With a burst better placed for the GBM’s detectors, or one bright enough to be seen by Fermi’s Large Area Telescope, even greater improvements are possible.

    The LIGO event was produced by the merger of two relatively large black holes, each about 30 times the mass of the sun. Binary systems with black holes this big were not expected to be common, and many questions remain about the nature and origin of the system.

    Black hole mergers were not expected to emit significant X-ray or gamma-ray signals because orbiting gas is needed to generate light. Theorists expected any gas around binary black holes would have been swept up long before their final plunge. For this reason, some astronomers view the GBM burst as most likely a coincidence and unrelated to GW150914. Others have developed alternative scenarios where merging black holes could create observable gamma-ray emission. It will take further detections to clarify what really happens when black holes collide.

    Albert Einstein predicted the existence of gravitational waves in his general theory of relativity a century ago, and scientists have been attempting to detect them for 50 years. Einstein pictured these waves as ripples in the fabric of space-time produced by massive, accelerating bodies, such as black holes orbiting each other. Scientists are interested in observing and characterizing these waves to learn more about the sources producing them and about gravity itself.

    NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

    For more information about NASA’s Fermi Gamma-ray Space Telescope, please visit:

    http://www.nasa.gov/fermi

    *Science paper:
    Fermi GBM Observations of LIGO Gravitational Wave event GW150914

    See the full article here .

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    The Fermi Gamma-ray Space Telescope , formerly referred to as the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.

     
  • richardmitnick 9:11 pm on April 29, 2016 Permalink | Reply
    Tags: , , , Polarity Reversals in the Earth's Magnetic Field   

    From Eos: “Polarity Reversals in the Earth’s Magnetic Field” 

    Eos news bloc

    Eos

    4.29.16
    Fabio Florindo

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    Apparent motions of the north geomagnetic pole recorded in sequences of lava flows during several reversals. Each colour corresponds to a distinct reversal record. Also shown in the center of the planet is the solid inner core (red) surrounded by the conducting liquid outer core (orange). Credit: Valet and Fournier*, 2016, doi:10.1002/2015RG000506

    Earth’s natural magnetic field is generated by complex motions of molten iron alloys in the outer core of the planet, at depths in excess of 2,900 km, and varies on time scales ranging from milliseconds to millions of years. At irregular intervals, lasting several hundred thousand years on average, one of the Earth’s most remarkable phenomena takes place: the Earth’s magnetic field reverses, and the North and South Magnetic Poles switch places relatively quickly. During the short time period between the two polarities the geomagnetic field changes can be magnetically recorded by sediments and by sequences of lava flows. These magnetic data are of value to paleomagnetists in reconstructing past geomagnetic fields and, more specifically, in constraining the structure and geometry of the transitional field more accurately.

    Studies of geomagnetic polarity reversals have generated huge debates in the paleomagnetic and wider solid Earth geophysics communities over the last 25 years. Some of these debates were among the most interesting ones in Earth Science over this period. Nevertheless, the topic has received less attention in recent years because of widespread difficulties and controversies concerning data reliability.

    A recent article published* in Reviews of Geophysics by Jean-Pierre Valet and Alexandre Fournier of Institut de Physique du Globe de Paris provides a mature reflection on the challenges faced in such research, with a critical review of the main reversal features derived from paleomagnetic records and analyses of some of these features in light of numerical simulations. As well as providing a critical review of past work, this contribution is sure to provide valuable direction for future research on the subject. AGU asked the authors of the article to highlight the important results that have emerged from their research and some of the important questions that remain.

    Why is this topic timely and important? What recent advances in particular are leading to a new understanding or synthesis?

    Reversals are one of the most enigmatic characteristic of the earth’s magnetic field and as so they generate many questions. How often do reversals occur and how long do they last? What is the field morphology when it reverses? Does the field weaken or collapse and then recovers with the opposite polarity? What are possible consequences of reversals for the biosphere? When should the next reversal happen? Reversals are relatively rare events if we compare their duration with the length of the polarity intervals. The unique observational evidence for the behavior of the field during a polarity reversal comes from records of the paleomagnetic field. For almost fifty years paleomagnetists attempted to gather information by studying sequences of lava flows and sediments which acquired their magnetization during their formation, and stored this signal over geological times. However reversals occur over a few thousand years at most and it is a real challenge to acquire detailed information over this short transitional period between the two polarities. In fact, there is no perfect magnetic recorder, most sediments are characterized by low temporal resolution and volcanism is sporadic in nature with lava flows irregularly distributed in time. Therefore, the results can be biased by artifacts that are not always fully understood so that many observations remain controversial. It was thus necessary to decipher the paleomagnetic records that have been gathered around the world by reviewing critically the dominant geomagnetic features. Recent progress in studies of geomagnetic reversals is also due to numerical simulations that have provided new insights into the mechanism of the geodynamo and its reversals. Despite being still far from the earth dynamo, hundreds of polarity reversals have been documented by numerical models. In many cases the numerical features are similar to the paleomagnetic observations, giving us the opportunity to compare and analyze data and simulations together.

    What are the implications for a broader understanding of Earth’s processes?

    The structure of geomagnetic polarity reversal remains largely unsolved. The geomagnetic field is maintained by rapid motions of the conductive iron-rich fluid in the outer core of the Earth. This liquid moves in complex ways as a result of convection within the core. There is now overall agreement that reversals occur without external forcing and therefore can be seen as an intrinsic property of the Earth’s dynamo. Therefore, determining the structure and processes associated with geomagnetic reversals is essential for a full understanding of the geodynamo processes. Typical timescales that characterize polarity reversals constrain the fluid dynamical timescales and hence our knowledge of the earth’s core. Reversals tell us also how the earth system responds to extreme global changes of the earth’s magnetic field.

    What are the major unsolved or unresolved questions and where are additional data or modeling efforts needed?

    The analysis of the database shows that the overall strength of the field, anywhere on the Earth, may be no more than a tenth of its strength now. Reversals seem to occur in several phases with a precursor and a rebound. We learned also that field geometry during the transition is much more complex with several poles wandering at the surface of the earth and can thus be described as a multipolar field. However it is very difficult to obtain a good description of the field geometry (quadrupolar, octopolar etc…) and to describe its time-evolution. This requires to obtain many detailed records of the same reversal (the last one being the best candidate) with good geographical coverage including in the southern hemisphere and the polar regions. Sedimentary records are only appropriate to reach this goal but most records collected from deep-sea sediments do not provide adequate resolution to unravel the field morphology constrained by the very rapidly changing nature of the non-dipole field that govern during the transition between the two polarities. Future studies will have to rely on very tiny specimens that require new technologies and on sequences of lava flows that are rare and discontinuous. Another objective is to constrain further the periods preceding and following the polarity reversals in order to better understand the processes leading to their occurrence. Of particular interest is the evolution of field intensity and specifically the decreasing and recovery phases prior and after each reversal. Detailed datasets would document how we switch from a stable dipolar dynamo to a reversing regime. Apart from promising developments generated by high resolution records of relative paleointensity in sediments, changes in cosmogenic isotope production such as beryllium 10 with its long half-life of 1.4 Ma, provide in principle another indirect estimate of geomagnetic intensity changes with time. 10Be production rate is constrained by penetration of cosmic particles inside the magnetosphere and, therefore, depends on the strength of magnetic field. Large 10Be production rate peaks are expected during periods of weak geomagnetic field intensities and, therefore, a significant 10Be production increase is observed during geomagnetic reversals.

    The past ten years have seen constructive interactions between the observational and modeling communities. Reversals produced by numerical dynamos that simulate more Earth’s like conditions will continue as computational power increases. There is no doubt that the convergence of both approaches will substantially improve our understanding of the nature of the geomagnetic reversals.

    *Science paper:
    Deciphering Records of Geomagnetic Reversals

    See the full article here .

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    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

     
  • richardmitnick 9:00 pm on April 29, 2016 Permalink | Reply
    Tags: , , , DEScientist of the Week: Ting Li   

    From DES: “DEScientist of the Week: Ting Li” 

    Dark Energy Icon

    The Dark Energy Survey

    April 29, 2016

    Meet Ting Li, Graduate Student at Texas A&M University!

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    Ting’s main research interest is to study the stellar substructure in our own Milky Way — dwarf galaxies and stellar streams. These features in the Milky Way can help us understand the nature of dark matter. She helps the team discover these stellar associations using DES data, and also follows them spectroscopically using the world’s largest optical telescopes, including Magellan Telescopes, the Vary Large Telescope, etc.

    6.5 meter Magellan Telescopes located at Carnegie’s Las Campanas Observatory, Chile.
    6.5 meter Magellan Telescopes located at Carnegie’s Las Campanas Observatory, Chile

    ESO/VLT at Cerro Paranal
    ESO/VLT at Cerro Paranal, Chile

    Apart from the scientific research, Ting also works on the DES infrastructures. Specifically, she works on the atmospheric transmission monitoring camera and the spectrophotometric calibration system for DECam. These two auxiliary systems will help DES to achieve high precision photometry, which is crucial for DES scientist to understand the nature of dark energy.

    We asked Ting a few more questions — here’s what she had to say:

    If you weren’t a scientist, what would your dream job be?

    I would want to be an astronaut, or more specifically, a job that can take me to space. Even if I could not go to space, I still hope that an instrument I build could go to space sometime in the future. I’m probably not physically strong enough to be qualified as a astronaut, but I’m good at astrophysics and instrumentation. I also speak many languages (English, Chinese, Japanese, little French and poor Spanish…). I still hope one day the dream would come true:)

    What is your secret talent?

    Ting-quisition: my graduate peers made this word for me, it means that Ting asks someone questions until that person “dies”. I’m not sure if that’s a talent or not, but I do like to ask questions and I learn a lot from asking.

    What do you think has been the most exciting advance in physics / astronomy in the last 10 years?

    Sky survey with CCDs, starting from SDSS.

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

    Astronomy has been significantly changed since the birth of CCDs and sky surveys. The progress is huge and revolutionary in the past 10 years. That’s why I joined DES and I think it will be the next revolution (before LSST starts).

    Thinking back to when you were an undergrad in physics (if applicable), was there anything you were taught then that is not taught now?

    I wish I had learned more about python and more about statistics.

    Any advice for aspiring scientists?

    This is the advice I would give to the students who might be considering going to graduate school and pursuing a career in scientific research.
    I would say that graduate school is tough, so make sure that’s what you want before you decide to go that route. If you decide to take it, then enjoy it. Graduate school is much more independent, compared to the undergraduate program. Instead of professors telling you what to do in your undergraduate study, you are the one who needs to make the decisions about yourself most of the time. You also have to learn a lot of new things by yourself and solve the problems by yourself. So make sure you pick a field that you like and you are interested in.
    The difficulties can sometimes be incredibly frustrating. However, part of getting closer to becoming a qualified Ph.D. is dealing with setbacks and experiencing failure. Maybe you don’t feel that you are gaining new knowledge every day, or maybe you feel that you are standing still after many days of hard work. But after several months or even years, you will know that you have already made a huge improvement in your research ability. You won’t see the changes every day, but be patient and persistent, and you will succeed.

    See the full article here .

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    DECam, built at FNAL
    DECam, built at FNAL
    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO Victor M Blanco Telescope at Cerro Tololo which houses the DECAm

    The Dark Energy Survey (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 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. This collaboration [has built] an extremely sensitive 570-Megapixel digital camera, DECam, and [has mounted] it on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory high in the Chilean Andes. Started in Sept. 2012 and continuing for five years, DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.

     
  • richardmitnick 8:45 pm on April 29, 2016 Permalink | Reply
    Tags: , Galaxy UGC 477,   

    From Hubble: “Hubble Sees Galaxy Hiding in the Night Sky” 

    NASA Hubble Banner

    NASA Hubble Telescope

    Hubble

    April 29, 2016
    Text credit: European Space Agency
    Image credit: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt

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    This striking NASA/ESA Hubble Space Telescope image captures the galaxy UGC 477, located just over 110 million light-years away in the constellation of Pisces (The Fish).

    UGC 477 is a low surface brightness (LSB) galaxy. First proposed in 1976 by Mike Disney, the existence of LSB galaxies was confirmed only in 1986 with the discovery of Malin 1. LSB galaxies like UGC 477 are more diffusely distributed than galaxies such as Andromeda and the Milky Way. With surface brightnesses up to 250 times fainter than the night sky, these galaxies can be incredibly difficult to detect.

    Most of the matter present in LSB galaxies is in the form of hydrogen gas, rather than stars. Unlike the bulges of normal spiral galaxies, the centers of LSB galaxies do not contain large numbers of stars. Astronomers suspect that this is because LSB galaxies are mainly found in regions devoid of other galaxies, and have therefore experienced fewer galactic interactions and mergers capable of triggering high rates of star formation.

    LSB galaxies such as UGC 477 instead appear to be dominated by dark matter, making them excellent objects to study to further our understanding of this elusive substance. However, due to an underrepresentation in galactic surveys — caused by their characteristic low brightness — their importance has only been realized relatively recently.

    See the full article here .

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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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  • richardmitnick 8:38 pm on April 29, 2016 Permalink | Reply
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    From Tartu: “European Organisation for Nuclear Research discusses Estonia’s potential membership” 

    U Tartu bloc

    University of Tartu

    CERN

    29.04.2016

    The delegation of the International Relations sector of the European Organisation for Nuclear Research, known as CERN, will visit Estonia on 2 and 3 May to get information about the circle of industry, research and decision makers in Estonia and establish direct contact for possible accession talks.

    In order for Estonian enterprises to be internationally more competitive, they need to produce more high-technology products with high added value. High added value means bigger salaries, bigger investments and bigger profit.

    According to Minister of Entrepreneurship Liisa Oviir, one way to achieve this, is to increase the so called institutional export to research centres, such as the European Space Agency (ESA) or CERN, which are known for their demanding and scientific technologically innovative solution orders.

    Last year, Estonia became a member of the ESA thanks to which our enterprises have received orders to develop high-technology products and services. Similarly to the ESA, CERN membership would also significantly increase the possibilities for Estonian enterprises to provide quality high-technology products and services all around the world.

    “Establishing closer high-level contacts is one prerequisite to better understand potential incomes and costs in a longer perspective. ESA has been a very positive example so far. The next step is to see what the options are to benefit from CERN in the longer perspective,” said Oviir.

    “Estonia’s research activity in CERN has gone upwards in recent years. Long-term research in high energy physics has been improved with cooperation to UT research groups in modelling the materials required for new accelerators and contributing to the development of high speed scintillators in medical technology. Participation in CERN programmes promotes the cooperation between Estonian enterprises and researchers and increases their capacity in research and development and innovation,” explained UT Vice Rector for Research Marco Kirm.

    CERN officials will meet Minister of Entrepreneurship Liisa Oviir, employees of the Ministry of Education and Research, visit enterprises in Tallinn and Sillamäe, the University of Tartu, Tallinn University of Technology and the National Institute of Chemical Physics and Biophysics.

    See the full article here .

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    U Tartu Campus

    UT is Estonia’s leading centre of research and training. It preserves the culture of the Estonian people and spearheads the country’s reputation in research and provision of higher education. UT belongs to the top 3% of world’s best universities.

    As Estonia’s national university, UT stresses the importance of international co-operation and partnerships with reputable research universities all over the world. The robust research potential of the university is evidenced by the fact that it is the only Baltic university that has been invited to join the Coimbra Group, a prestigious club of renowned research universities.

    UT includes nine faculties and four colleges. To support and develop the professional competence of its students and academic staff, the university has entered into bilateral co-operation agreements with 64 partner institutions in 23 countries.

     
  • richardmitnick 8:27 pm on April 29, 2016 Permalink | Reply
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    From astrobites: “A PeVatron at the Galactic Center” 

    Astrobites bloc

    Astrobites

    Apr 29, 2016
    Kelly Malone

    Science paper: Acceleration of petaelectronvolt protons in the Galactic Centre
    Authors: The HESS Collaboration
    Status: Published in Nature

    In the past, we’ve talked on this website a bit about the mysteries of galactic cosmic rays, or charged particles from outer space that are mainly made up of protons. These particles can reach PeV energies and beyond, but the shocks of supernova remnants (the origin of most galactic cosmic rays) cannot accelerate particles to these high energies. The HESS Collaboration analyzed 10 years of gamma-ray observations and have seen evidence of a PeVatron (PeV accelerator) in the center of our galaxy. If confirmed, this would be the first PeVatron in our galaxy.

    As mentioned above, the HESS Collaboration used observations of gamma rays from their array of telescopes to do this analysis.

    HESS Cherenko Array
    HESS Cherenko Array

    Gamma rays are often used to probe the nature of cosmic ray accelerators; this is because they are associated with these sites, but unlike the charged cosmic rays, they are electrically neutral and therefore don’t bend in magnetic fields on their way to Earth (i.e. they point back to the source).

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    Figure 1: HESS’s very high energy gamma ray map of the Galactic Center region. The color scale shows the number of gamma rays per pixel, while the white contour lines illustrate the distribution of molecular gas. Their correlation points to a hadronic origin of gamma ray emission. The right panel is simply a zoomed view of the inner portion. (Source: Figure 1 from the paper)

    2
    Figure 2: The red shaded area shows the 1 sigma confidence band of the measured gamma-ray spectrum of the diffuse emission in the region of interest. The red lines show different models, assuming that the gamma rays are coming from neutral pion decay after the pions have been produced in proton-proton interactions. Note the lack of cutoff at high energies, indicating that the parent protons have energies in the PeV range. The blue data points refer to another gamma-ray source in the region, HESS J1745-290. The link between these two objects is currently unknown.

    The area they studied is known as the Central Molecular Zone, which surrounds the Galactic Center. They found that the distribution of gamma rays mirrored the distribution of the gas-rich areas, which points to a hadronic (coming from proton interactions) origin of the gamma rays. From the gamma-ray luminosity and amount of gases in the area, it can be shown that there must be at least one cosmic ray accelerator in the region. Additionally, the energy spectrum of the diffuse gamma-ray emission from the region around Sagittarius A* (the location of the black hole at at the Galactic Center) does not have an observed cutoff or a break in the TeV energy range. This means that the parent proton population that created these gamma rays should have energies of ~1 PeV (the PeVatron). Just to refresh everyone’s memory, a TeV is 10^12 electronvolts, while a PeV is 10^15 electronvolts. A few TeV is about the limit of what can be produced in particle laboratories on Earth (the LHC reaches 14 TeV). A PeV is roughly 1000 times that!

    What is the source of these protons? The typical explanation for Galactic cosmic rays, supernova remnants, is unlikely here: in order to match the data and inject enough cosmic rays into the Central Molecular Zone, the authors estimate that we would need more than 10 supernova events over 1000 years. This is a very high rate that is improbable.

    Instead, they hypothesize that Sgr A* is the source of these protons.

    Sag A* NASA's Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    They could either be accelerate in the accretion flow immediately outside the black hole, or further away where the outflow terminates. They do note that the required acceleration rate is a few orders of magnitude above the current luminosity, but that the black hole may have been much more active in the past, leading to higher production rates of the protons and other nuclei. If this is true, it could solve one of the most puzzling mysteries in cosmic ray physics: the origin of the higher energy galactic cosmic rays.

    See the full article here .

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    What do we do?

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

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

     
  • richardmitnick 6:38 pm on April 29, 2016 Permalink | Reply
    Tags: , , , Oxygen Abundance in Giant Stars   

    From CfA: “Oxygen in Stars” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    April 29, 2016

    1
    An optical image of the brightest globular cluster, Omega Centauri, a group of over ten million stars older than the Sun. Astronomers have developed a new computational method to determine the abundance of oxygen in these and similar stars, and in particular in giant stars. The code finds values that are more self-consistent than previous estimates. Joaquin Polleri & Ezequiel Etcheverry, Observatorio Panameño en San Pedro de Atacama

    Oxygen is the third most abundant element in the universe, after hydrogen and helium. It is an important constituent of the clouds of gas and dust in space, especially when combined in molecules with other atoms like carbon, and it is from this interstellar material that new stars and planets develop. Oxygen is, of course, also essential for life as we know it, and all known life forms require liquid water and its oxygen content. Oxygen in molecular form, especially as water, was supposed to be relatively abundant, but over the past decade considerable attention has been paid to observations suggesting that at least in molecular form oxygen is scarcer than expected, a deficit that has not yet been entirely resolved.

    Atomic oxygen by contrast, seen most prominently in the light of stars, was thought to be in good agreement with expectations. The neutral oxygen atom produces strong lines that are frequently used to calculate its abundance. Models fit the line strengths by taking into account the radiation field, the star’s hot gas motions, and the internal structure of the star (for example, the way the temperature and pressure change with radius). It turns out, however, that varying assumptions in these calculations can result in oxygen abundance predictions that differ significantly, and in the case of giant stars, which are larger and cooler and often have hot outer chromospheres, those abundance results can disagree with one another by as much as a factor of 15. This discrepancy has often been discounted by scientists arguing that some of the proposed stellar models are themselves unrealistic.

    CfA astronomers Andrea Dupree, Eugene Avrett, and Bob Kurucz have tacked this fundamental problem with Avrett’s PANDORA code for stellar atmospheres. In particular, they include the effects of a hot outer atmosphere in giant stars, something that was typically ignored. Moreover, they do not tie the excitation of oxygen atoms (and the corresponding line strengths) to the local temperature. That constraint, imposed by most previous methods in order to simplify the calculations, does not take more complex situations (like the hot atmosphere) adequately into account. The astronomers find that their new computations can resolve several outstanding issues. The lines themselves are actually as much as three times stronger than previously thought, reducing the implied oxygen abundances, and thereby also affecting details of the stellar interior models, especially for giants seen in globular clusters of stars. Similar improvements are seen in the results for stars known to be lacking other heavier elements, and even some normal, Sun-like stars. The possible implications extend to estimating more accurately the amount of oxygen present in a solar nebula when exoplanets form.

    Science paper:
    Chromospheric Models and the Oxygen Abundance in Giant Stars, A. K. Dupree, E. H. Avrett, and R. L. Kurucz, ApJ 821, L7, 2016

    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 6:27 pm on April 29, 2016 Permalink | Reply
    Tags: , , Planet habitability   

    From Eos: “Becoming Habitable in the Habitable Zone” 

    Eos news bloc

    Eos

    4.29.16
    Sarah Stanley

    1
    An artist’s rendition of Kepler-186f, an Earth-size planet in the habitable zone of a distant solar system. Little is known about its composition, but if it turns out to be rocky like Earth, it may be subject to climate-mantle-core interactions that determine whether it can actually sustain life. Credit: NASA Ames/SETI Institute/JPL-Caltech

    Day to day, plate tectonics may seem to have little to do with Earth’s habitability. However, over time, interactions between our planet’s climate, mantle, and core have created a suitable home for complex life.

    Techtonic plates, USGS, 1996
    The tectonic plates of the world were mapped in 1996, USGS.

    In a new review paper*, Foley and Driscoll suggest that similar processes could set other rocky planets on very different trajectories, ultimately determining whether they could support life as we know it.

    Cooler climates promote plate tectonics by keeping plate boundaries from fusing and by weakening the crust and outer mantle. In turn, plate tectonics help keep the climate temperate through carbon cycling. On Earth, cold slabs of rock subduct and sink deep into the mantle, drawing heat from the core. Long-term core cooling helps maintain Earth’s magnetic field, which keeps the solar wind from stripping away the atmosphere.

    The authors hypothesize that the climate-mantle-core connection determines whether a young, rocky planet will develop plate tectonics, a temperate climate, and a magnetic field—all of which are thought to be necessary for life. Initial atmospheric composition, timing of the onset of plate tectonics, and other factors can affect how climate-mantle-core dynamics unfold. This means that two similar planets might follow wildly different paths, even if they both reside in a solar system’s habitable zone (where liquid water can exist on the surface).

    The authors also suggest that interactions between the climate, mantle, and core might explain why Earth and Venus are so different, despite their similar sizes and composition: Venus’s hot climate prevents plate tectonics, stifling a sustained magnetic field.

    Scientists don’t yet know enough Venusian history to confirm the authors’ hypothesis. Much more research is also needed to clarify connections between climate, mantle, and core for rocky planets in general, but a better understanding of these dynamics could help predict the likelihood of finding an Earth-like exoplanet. (Geochemistry, Geophysics, Geosystems, doi:10.1002/2015GC006210, 2016).

    *Science paper:
    Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

    See the full article here .

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    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

     
  • richardmitnick 3:40 pm on April 29, 2016 Permalink | Reply
    Tags: , , Speed of Gravity,   

    From Ethan Siegel: “Why Does Gravity Move At The Speed Of Light?” 

    Starts with a Bang

    4.28.16
    Ethan Siegel

    1
    Image credit: European Gravitational Observatory, Lionel BRET/EUROLIOS.

    If you looked out at the Sun across the 93 million miles of space that separate our world from our nearest star, the light you’re seeing isn’t from the Sun as it is right now, but rather as it was some 8 minutes and 20 seconds ago. This is because as fast as light is — moving at the speed of light — it isn’t instantaneous: at 299,792.458 kilometers per second (186,282 miles per second), it requires that length of time to travel from the Sun’s photosphere to our planet. But gravitation doesn’t necessarily need to be the same way; it’s possible, as Newton’s theory predicted, that the gravitational force would be an instantaneous phenomenon, felt by all objects with mass in the Universe across the vast cosmic distances all at once.

    2
    Image credit: NASA/JPL-Caltech, for the Cassini mission.

    But is that right? If the Sun were to simply wink out of existence, would the Earth immediately fly off in a straight line, or would it continue orbiting the Sun’s location for another 8 minutes and 20 seconds? If you ask General Relativity, the answer is much closer to the latter, because it isn’t mass that determines gravitation, but rather the curvature of space, which is determined by the sum of all the matter and energy in it. If you were to take the Sun away, space would go from being curved to being flat, but that transformation isn’t instantaneous. Because spacetime is a fabric, that transition would have to occur in some sort of “snapping” motion, which would send very large ripples — i.e., gravitational waves — through the Universe, propagating outward like ripples in a pond.

    3
    Image credit: Sergiu Bacioiu from Romania, under c.c.-2.0 generic.

    The speed of those ripples is determined the same way the speed of anything is determined in relativity: by their energy and their mass. Since gravitational waves are massless yet have a finite energy, they must move at the speed of light! Which means, if you think about it, that the Earth isn’t directly attracted to the Sun’s location in space, but rather to where the Sun was located a little over 8 minutes ago.

    4
    Image credit: David Champion, Max Planck Institute for Radio Astronomy.

    If that were the only difference between Einstein’s theory of gravity and Newton’s, we would have been able to instantly conclude that Einstein’s theory was wrong. The orbits of the planets were so well studied and so precisely recorded for so long (since the late 1500s!) that if gravity simply attracted the planets to the Sun’s prior location at the speed of light, the planets’ predicted locations would mismatch severely with where they actually were. It’s a stroke of brilliance to realize that Newton’s laws require an instantaneous speed of gravity to such precision that if that were the only constraint, the speed of gravity must have been more than 20 billion times faster than the speed of light!

    But in General Relativity, there’s another piece to the puzzle that matters a great deal: the orbiting planet’s velocity as it moves around the Sun. The Earth, for example, since it’s also moving, kind of “rides” over the ripples traveling through space, coming down in a different spot from where it was lifted up. It looks like we have two effects going on: each object’s velocity affects how it experiences gravity, and so do the changes that occur in gravitational fields.

    5
    Image credit: LIGO/T. Pyle, of a model of distorted space in the Solar System.

    What’s amazing is that the changes in the gravitational field felt by a finite speed of gravity and the effects of velocity-dependent interactions cancel almost exactly! The inexactness of the cancellation is what allows us to determine, observationally, if Newton’s “infinite speed of gravity” model or Einstein’s “speed of gravity = speed of light” model matches with our Universe. In theory, we know that the speed of gravity should be the same as the speed of light. But the Sun’s force of gravity out here, by us, is far too weak to measure this effect. In fact, it gets really hard to measure, because if something moves at a constant velocity in a constant gravitational field, there’s no observable affect at all. What we’d want, ideally, is a system that has a massive object moving with a changing velocity through a changing gravitational field. In other words, we want a system that consists of a close pair of orbiting, observable stellar remnants, at least one of which is a neutron star.


    Access mp4 video here .

    As one or both of these neutron stars orbit, they pulse, and the pulses are visible to us here on Earth each time the pole of a neutron star passes through our line-of-sight. The predictions from Einstein’s theory of gravity are incredibly sensitive to the speed of light, so much so that even from the very first binary pulsar system discovered in the 1980s, PSR 1913+16 (or the Hulse-Taylor binary), we have constrained the speed of gravity to be equal to the speed of light with a measurement error of only 0.2%!

    6
    Image credit: NASA (L), Max Planck Institute for Radio Astronomy / Michael Kramer, via http://www.mpg.de/7644757/W002_Physics-Astronomy_048-055.pdf.

    That’s an indirect measurement, of course. We were able to do another type of indirect measurement in 2002, when a chance coincidence lined up the Earth, Jupiter, and a very strong radio quasar (QSO J0842+1835) all along the same line-of-sight! As Jupiter moved between Earth and the quasar, the gravitational bending of Jupiter allowed us to measure the speed of gravity, ruling out an infinite speed and determining that the speed of gravity was between 2.55 × 10^8 and 3.81 × 10^8 meters-per-second, completely consistent with Einstein’s predictions.

    7
    The quasar QSO J0842+1835, whose path was gravitationally altered by Jupiter in 2002, allowing an indirect confirmation that the speed of gravity equals the speed of light. Image credit: Fomalont et al. (2000), ApJS 131, 95-183, via http://www.jive.nl/svlbi/vlbapls/J0842+1835.htm.

    Ideally, we’d be able to measure the speed of these ripples directly, from the direct detection of a gravitational wave. LIGO just saw the first one, after all! Unfortunately, due to our inability to correctly triangulate the location from which these waves originated, we don’t know from which direction the waves were coming. By calculating the distance between the two independent detectors (in Washington and Louisiana) and measuring the difference in the signal arrival time, we can determine that the speed of gravity is consistent with the speed of light, but can only place an absolute constraint that it’s equal to the speed of light within 70%.

    8
    The gravitational wave arrival at the two detectors in WA and LA, with an uncertain origin to their direction. Image credit: Diego Blas, Mikhail M. Ivanov, Ignacy Sawicki, Sergey Sibiryakov, via https://arxiv.org/abs/1602.04188.

    Still, it’s the indirect measurements from very rare pulsar systems that give us the tightest constraints. The best results, at the present time, tell us that the speed of gravity is between 2.993 × 10^8 and 3.003 × 10^8 meters per second, which is an amazing confirmation of General Relativity and a terrible difficulty for alternative theories of gravity that don’t reduce to General Relativity! (Sorry, Newton!) And now you know not only what the speed of gravity is, but where to look to figure it out!

    See the full article here .

    Please help promote STEM in your local schools.

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    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 3:01 pm on April 29, 2016 Permalink | Reply
    Tags: , , , Superluminous Supernova   

    From DES- “From the DArchive: A Newly Discovered Superluminous Supernova” 

    Dark Energy Icon

    The Dark Energy Survey

    April 29, 2016
    Mathew Smith
    Edited by R.C. Wolf & R. Cawthon

    Science paper:
    DES14X3taz: A Type I Superluminous Supernova Showing a Luminous, Rapidly Cooling Initial Pre-Peak Bump

    In this paper we present DES14X3taz, a newly discovered superluminous supernova (SLSN). This particular SLSN is very unusual – if you look at the evolution of its brightness over time, or its light curve, there are two peaks (most only have one)! In our analysis, we attempt to explain what physical process might cause such an occurrence and determine if this is truly a unique event or common to all SLSNe.

    Although the initial DECam data was fairly indicative that this was a particularly interesting object, we had to use additional information to confirm our discovery. By combining optical light-curve data from DES and its sister survey, the Survey Using Decam for Superluminous Supernovae (SUDSS), we were able to plot the evolution of brightness over time (light-curve) of DES14X3taz and find its brightest point. We then used spectra obtained on the Gran Telescopino Canarias (GTC) in La Palma, Spain to estimate the distance to this event, and thus its peak brightness, and unambiguously confirmed that it is a SLSNe.

    Gran Telescopino Canarias exterior
    Gran Telescopino de Canaries interior
    Gran Telescopino de Canaries

    What really distinguishes DES14X3taz from previously discovered SLSNe is the presence of an early “bump” in the light curve prior to the main light-curve. The figure below shows these features for DES14X3taz.

    1

    In addition to detecting this bump, we were lucky to have observed this SLSN before explosion and to have observed it at many points during its lifetime; most other observed SLSNe have been discovered post-explosion or do not have such a large a sample of measurements.

    Our observations with DECam allowed us to obtain colour information, from observations in several filters, of the bump. This enabled us to probe the physical processes driving these super-luminous events by comparing our data to pre-existing theoretical models. In the figure below, the colored-circle points are real data, and the dashed lines represent theoretical observations for different physical processes that we think might be motivating this behavior.

    2

    Fitting models to the main curve show that the physical mechanism driving the explosion is consistent with a magnetar, a rapidly rotating neutron star (as seen in the match to the Extended Material Around the Star). In the figure, this is consistent with the solid lines. Fitting black-body curves to the DES data of DES14X3taz, we show that the initial peak cools rapidly, before a period of reheating, which drives the main part of the light-curve. Using chi-squared statistics, we compare photometric data of the initial peak with various models of shock-cooling and find that shock from material at an extended radius is consistent with observations. We also find a sample of previously discovered SLSNe that also exhibit this early bump in their light curves; therefore, we believe our findings suggest a unified physical interpretation for all SLSNe.

    SLSNe are a new class of transient event, with potentially exciting consequences for cosmology. Recent work (Inserra & Smartt 2014) has suggested that these events may even be “standardisable candles”, and thus useful to measure distances to the high redshift Universe. As these events are more luminous than traditional Type Ia supernovae they have the potential to extend SN cosmology to larger distances than currently possible. However, little is well-understood about the explosion mechanism driving these events and we will need to understand more about the origin of SLSNe as we explore utilizing them as cosmological probes.

    See the full article here .

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    DECam, built at FNAL
    DECam, built at FNAL
    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO Victor M Blanco Telescope at Cerro Tololo which houses the DECAm

    The Dark Energy Survey (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 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. This collaboration [has built] an extremely sensitive 570-Megapixel digital camera, DECam, and [has mounted] it on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory high in the Chilean Andes. Started in Sept. 2012 and continuing for five years, DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.

     
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