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  • richardmitnick 12:45 pm on April 30, 2019 Permalink | Reply
    Tags: "Something's Glowing at The Heart of Our Galaxy But It May Not Be What We Thought", , , , , , NASA’s Fermi Gamma-ray Space Telescope,   

    From MIT News via Science Alert: “Something’s Glowing at The Heart of Our Galaxy, But It May Not Be What We Thought” 

    MIT News
    MIT Widget

    From MIT News



    Science Alert

    30 APR 2019

    (NASA/DOE/Fermi LAT Collaboration)

    NASA/Fermi LAT

    NASA/Fermi Gamma Ray Space Telescope

    Something is glowing at the heart of the Milky Way – there’s more diffuse gamma radiation than can be explained by what we can directly observe. It’s called the Galactic Center GeV Excess (GCE), and astronomers have been trying to explain it for years.

    One idea was that the glow is produced by the annihilation of dark matter. Then, it began to look like the culprit was actually millisecond pulsars that have somehow eluded detection. Now, a new paper could bring dark matter back into the game.

    Using simulated data, theoretical astrophysicists Rebecca Leane and Tracy Slatyer of MIT have found a flaw in the millisecond pulsar analyses.

    “We discover striking behaviour consistent with a mismodelling effect in the real Fermi data, finding that large artificial injected dark matter signals are completely misattributed to point sources [i.e., millisecond pulsars],” they wrote in their paper , Dark Matter Strikes Back at the Galactic Center.

    It’s yet to be peer-reviewed, but if their calculations pass muster, the paper could blow the GCE debate wide open again.

    It first arose about 10 years ago, when physicists noticed an excess of gamma radiation in the data collected by the Fermi Gamma Ray Space Telescope.

    They thought that the culprit could be long-hypothesised, never observed dark matter annihilation: Even though we can’t detect dark matter directly, it could be producing radiation we can see.

    If types of dark matter particles called Weakly Interacting Massive Particles, or WIMPs, were to collide with each other – like the collisions generated by particle accelerators – they would annihilate each other, exploding in a shower of other particles, including gamma-ray photons.

    This should produce a pretty recognisable signal – an even distribution of these photons. But two separate statistical analyses published in 2016, Strong support for the millisecond pulsar origin of the Galactic center GeV excess in: Physical Review Letters, and Evidence for Unresolved Gamma-Ray Point Sources in the Inner Galaxy in: Physical Review Letters one of which was co-authored by Slatyer, found the photons distributed in clumps instead.

    The source, they concluded, was more likely a population of millisecond pulsars, neutron stars that rotate up to 1,000 times per second. They were too faint to be detected individually, instead producing a diffuse glow.

    So, Slatyer and Leane mathematically simulated the Milky Way, adding in a few more pulsars as well as dark matter annihilation. They found that, even when they added dark matter as the source of some of the GCE, an analysis using the same methods from 2016 still misidentified the origin as millisecond pulsars and gamma radiation from the Fermi bubbles blown by the supermassive black hole in the galactic core.

    Now, this doesn’t mean that the dark matter is there. It just shows that the analytical methods used to locate the source of the GCE in 2016 are likely unreliable. That there’s something scientists don’t understand fully.

    “Something about our understanding of the gamma rays is missing at this stage,” Leane told Quanta. “It’s possible to hide a dark matter signal, if it were really there.”

    Two other recent preprint papers, Scrutinizing the evidence for dark matter in cosmic-ray antiprotons and Scrutinizing the evidence for dark matter in cosmic-ray antiprotons seem to be adding support, too. They found larger than expected amounts of antiprotons in spectrometer data, another possible by-product of dark matter annihilation.

    At the moment, though, the results are unconfirmed by the peer-review community, so the jury remains well and truly out, and millisecond pulsars remain firmly on the table.

    But the game ain’t over for dark matter yet, either.

    See the full article here .

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  • richardmitnick 1:09 pm on October 12, 2018 Permalink | Reply
    Tags: , , , , Dame Susan Jocelyn Bell Burnell discovered pulsars with radio astronomy at the Mullard Radio Astronomy Observatory Cambridge University-Denied the Nobel., , NASA’s Fermi Gamma-ray Space Telescope,   

    From NASA Goddard Space Flight Center: “‘Pulsar in a Box’ Reveals Surprising Picture of a Neutron Star’s Surroundings” 

    NASA Goddard Banner
    From NASA Goddard Space Flight Center

    Oct. 10, 2018
    Francis Reddy
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    An international team of scientists studying what amounts to a computer-simulated “pulsar in a box” are gaining a more detailed understanding of the complex, high-energy environment around spinning neutron stars, also called pulsars.

    ‘Pulsar in a Box’ Reveals Surprises in Neutron Star’s Surroundings | NASA

    Explore a new “pulsar in a box” computer simulation that tracks the fate of electrons (blue) and their antimatter kin, positrons (red), as they interact with powerful magnetic and electric fields around a neutron star. Lighter tracks indicate higher particle energies. Each particle seen in this visualization actually represents trillions of electrons or positrons. Better knowledge of the particle environment around neutron stars will help astronomers understand how they produce precisely timed radio and gamma-ray pulses.
    Credits: NASA’s Goddard Space Flight Center

    The model traces the paths of charged particles in magnetic and electric fields near the neutron star, revealing behaviors that may help explain how pulsars emit gamma-ray and radio pulses with ultraprecise timing.

    “Efforts to understand how pulsars do what they do began as soon as they were discovered in 1967, and we’re still working on it,” said Gabriele Brambilla, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Milan who led a study of the recent simulation.

    Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

    Dame Susan Jocelyn Bell Burnell 2009

    “Even with the computational power available today, tracking the physics of particles in the extreme environment of a pulsar is a considerable challenge.”

    A pulsar is the crushed core of a massive star that ran out of fuel, collapsed under its own weight and exploded as a supernova. Gravity forces more mass than the Sun’s into a ball no wider than Manhattan Island in New York City while also revving up its rotation and strengthening its magnetic field. Pulsars can spin thousands of times a second and wield the strongest magnetic fields known.

    These characteristics also make pulsars powerful dynamos, with superstrong electric fields that can rip particles out of the surface and accelerate them into space.

    NASA’s Fermi Gamma-ray Space Telescope has detected gamma rays from 216 pulsars.

    NASA/Fermi LAT

    NASA/Fermi Gamma Ray Space Telescope

    Observations show that the high-energy emission occurs farther away from the neutron star than the radio pulses. But exactly where and how these signals are produced remains poorly known.

    Various physical processes ensure that most of the particles around a pulsar are either electrons or their antimatter counterparts, positrons.

    “Just a few hundred yards above a pulsar’s magnetic pole, electrons pulled from the surface may have energies comparable to those reached by the most powerful particle accelerators on Earth,” said Goddard’s Alice Harding. “In 2009, Fermi discovered powerful gamma-ray flares from the Crab Nebula pulsar that indicate the presence of electrons with energies a thousand times greater.”

    X-ray picture of Crab pulsar, taken by Chandra

    Supernova remnant Crab nebula. NASA/ESA Hubble

    Speedy electrons emit gamma rays, the highest-energy form of light, through a process called curvature radiation. A gamma-ray photon can, in turn, interact with the pulsar’s magnetic field in a way that transforms it into a pair of particles, an electron and a positron.

    To trace the behavior and energies of these particles, Brambilla, Harding and their colleagues used a comparatively new type of pulsar model called a “particle in cell” (PIC) simulation. Goddard’s Constantinos Kalapotharakos led the development of the project’s computer code. In the last five years, the PIC method has been applied to similar astrophysical settings by teams at Princeton University in New Jersey and Columbia University in New York.

    “The PIC technique lets us explore the pulsar from first principles. We start with a spinning, magnetized pulsar, inject electrons and positrons at the surface, and track how they interact with the fields and where they go,” Kalapotharakos said. “The process is computationally intensive because the particle motions affect the electric and magnetic fields and the fields affect the particles, and everything is moving near the speed of light.”

    The simulation shows that most of the electrons tend to race outward from the magnetic poles. The positrons, on the other hand, mostly flow out at lower latitudes, forming a relatively thin structure called the current sheet. In fact, the highest-energy positrons here — less than 0.1 percent of the total — are capable of producing gamma rays similar to those Fermi detects, confirming the results of earlier studies.

    Some of these particles likely become boosted to tremendous energies at points within the current sheet where the magnetic field undergoes reconnection, a process that converts stored magnetic energy into heat and particle acceleration.

    One population of medium-energy electrons showed truly odd behavior, scattering every which way — even back toward the pulsar.

    The particles move with the magnetic field, which sweeps back and extends outward as the pulsar spins. Their rotational speed rises with increasing distance, but this can only go on so long because matter can’t travel at the speed of light.

    The distance where the plasma’s rotational velocity would reach light speed is a feature astronomers call the light cylinder, and it marks a region of abrupt change. As the electrons approach it, they suddenly slow down and many scatter wildly. Others can slip past the light cylinder and out into space.

    The simulation ran on the Discover supercomputer at NASA’s Center for Climate Simulation at Goddard and the Pleiades supercomputer at NASA’s Ames Research Center in Silicon Valley, California.

    NASA Discover SGI Supercomputer- NASA’s Center for Climate Simulation Primary Computing Platform

    NASA SGI Intel Advanced Supercomputing Center Pleiades Supercomputer

    The model actually tracks “macroparticles,” each of which represents many trillions of electrons or positrons. A paper describing the findings was published May 9 in The Astrophysical Journal

    “So far, we lack a comprehensive theory to explain all the observations we have from neutron stars. That tells us we don’t yet completely understand the origin, acceleration and other properties of the plasma environment around the pulsar,” Brambilla said. “As PIC simulations grow in complexity, we can expect a clearer picture.”

    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 about NASA’s Fermi mission, visit:


    See the full article here.


    Please help promote STEM in your local schools.

    Stem Education Coalition

    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

    NASA/Goddard Campus

  • richardmitnick 8:21 am on August 26, 2018 Permalink | Reply
    Tags: , , NASA’s Fermi Gamma-ray Space Telescope, One photon emitted during the solar minimum had an energy as high as 467.7 GeV, , , Strange gamma rays from the sun may help decipher its magnetic fields, The high-energy light is more plentiful and weirder than anyone expected   

    From Science News: “Strange gamma rays from the sun may help decipher its magnetic fields” 

    From Science News

    August 24, 2018
    Lisa Grossman

    The high-energy light is more plentiful and weirder than anyone expected.

    A TANGLED SKEIN The sun’s knotted magnetic fields, visualized here as white lines, scramble cosmic rays and may cause them to shoot energetic light called high-energy gamma rays toward Earth. Solar Dynamics Observatory/GSFC/NASA


    The sleepy sun turns out to be a factory of extremely energetic light.

    Scientists have discovered that the sun puts out more of this light, called high-energy gamma rays, overall than predicted. But what’s really weird is that the rays with the highest energies appear when the star is supposed to be at its most sluggish, researchers report in an upcoming study in Physical Review Letters. The research is the first to examine these gamma rays over most of the solar cycle, a roughly 11-year period of waxing and waning solar activity.

    That newfound oddity is probably connected to the activity of the sun’s magnetic fields, the researchers say, and could lead to new insights about the mysterious environment.

    “The almost certain thing that’s going on here is the magnetic fields are much more powerful, much more variable, and much more weirdly shaped than we expect,” says astrophysicist John Beacom of the Ohio State University in Columbus.

    The sun’s high-energy gamma rays aren’t produced directly by the star. Instead, the light is triggered by cosmic rays — protons that zip through space with some of the highest energies known in nature — that smack into solar protons and produce high-energy gamma rays in the process (SN: 10/14/27, p. 7).

    All of those gamma rays would get lost inside the sun, if not for magnetic fields. Magnetic fields are known to take charged particles like cosmic rays and spin them around like a house in a tornado. Theorists have predicted that cosmic rays whose paths have been scrambled by the tangled mass of magnetic fields at the solar surface should send high-energy gamma rays shooting back out of the sun, where astronomers can see them.

    Beacom and colleagues, led by astrophysicist Tim Linden of Ohio State, sifted through data from NASA’s Fermi Gamma-ray Space Telescope from August 2008 to November 2017.

    NASA/Fermi LAT

    NASA/Fermi Gamma Ray Space Telescope

    The observations spanned a period of low solar activity in 2008 and 2009, a period of higher activity in 2013 and a decline in activity to the minimum of the next cycle, which started in 2018 (SN: 11/2/13, p. 22). The team tracked the number of solar gamma rays emitted per second, as well as their energies and where on the sun they came from.

    There were more high-energy gamma rays, above 50 billion electron volts, or GeV, than anyone predicted, the team reports. Weirder still, rays with energies above 100 GeV appeared only during the solar minimum, when the sun’s activity level was low. One photon emitted during the solar minimum had an energy as high as 467.7 GeV.

    Strangest of all, the sun seems to emit gamma rays from different parts of its surface at different times in its cycle. Because cosmic rays that hit the sun come in from all directions, you would expect the entire sun to light up in gamma rays uniformly. But Beacom’s team found that during the solar minimum, gamma rays came mainly from near the equator, and during the solar maximum, when the sun’s activity level was high, they clustered near the poles.

    “All of these things are way more weird than anyone had predicted,” Beacom says. “And that means the magnetic fields must be way more weird than anyone had thought.”
    The missing middle

    These plots show that the sun shot light called high-energy gamma rays from its middle during a period of low solar activity (from about August 2008 to the end of 2009, left), but not during a period of high activity (from 2010 until 2017, right). The gamma rays seem to migrate from the equator to the poles after 2010. Rays with less than 100 billion electron volts, or GeV, of energy are depicted as circles; those with 100 GeV or more are triangles. The bar graphs represent the number of gamma rays that came from different latitudes.

    T. Linden et al/Physical Review Letters 2018

    Beacom and colleagues tried to connect the excess gamma rays to other solar behaviors that change with magnetic activity, like solar flares or sunspots (SN: 9/30/17, p. 6). “So far nothing has really held up to any sort of scrutiny,” says astrophysicist Annika Peter, also at Ohio State.

    High-energy gamma rays may offer a new way to probe the magnetic fields in the uppermost layer of the solar surface, called the photosphere. “You can’t see [the fields] with a telescope,” Beacom says. “But these [cosmic rays] are journeying there, and the gamma rays they send back are messengers of the terrible conditions there.”

    More observations are coming soon. NASA’s Parker Solar Probe, which launched on August 12, will take the first direct measurements of the magnetic field in the sun’s outer atmosphere, or corona (SN: 7/21/18, p. 12).


    NASA Parker Solar Probe Plus

    And as the sun enters the next solar minimum, the highest-energy gamma rays are starting to return. In February, Fermi caught its first gamma ray with an energy above 100 GeV since 2009.

    “There really is something strange afoot,” says solar physicist Craig DeForest of the Southwest Research Institute, who is based in Boulder, Colo., and was not involved in the work. “When there’s some new discovery, scientists don’t shout ‘Eureka!’ They go, ‘Hm, that’s funny. That can’t be right.’ This is a classic case of that.”

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

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