Tagged: NASA Fermi Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 8:47 pm on July 13, 2015 Permalink | Reply
    Tags: , , Blazars, NASA Fermi   

    From NASA Fermi: “NASA’s Fermi Sees Record Flare from a Black Hole in a Distant Galaxy” 


    Fermi

    July 10, 2015
    Francis Reddy
    NASA’s Goddard Space Flight Center

    Five billion years ago, a great disturbance rocked a region near the monster black hole at the center of galaxy 3C 279.

    1
    3C 279
    EGRET team, Compton Observatory, NASA
    26 December 1998

    On June 14, the pulse of high-energy light produced by this event finally arrived at Earth, setting off detectors aboard NASA’s Fermi Gamma-ray Space Telescope and other satellites. Astronomers around the world turned instruments toward the galaxy to observe this brief but record-setting flare in greater detail.

    “One day 3C 279 was just one of many active galaxies we see, and the next day it was the brightest thing in the gamma-ray sky,” said Sara Cutini, a Fermi Large Area Telescope scientist at the Italian Space Agency’s Science Data Center in Rome.

    1
    Blazar 3C 279’s historic gamma-ray flare can be seen in this image from the Large Area Telescope (LAT) on NASA’s Fermi satellite. Gamma rays with energies from 100 million to 100 billion electron volts (eV) are shown; for comparison, visible light has energies between 2 and 3 eV. The image spans 150°, is shown in a stereographic projection, and represents an exposure from June 11 at 00:28 UT to June 17 at 08:17 UT. The scale bar at left shows an angular distance of 10°, which is about the width of a clenched fist at arm’s length. During the flare, the blazar outshone the Vela pulsar, usually the brightest object in the gamma-ray sky. NASA/DOE/Fermi LAT Collaboration

    3C 279 is a famous blazar, a galaxy whose high-energy activity is powered by a central supermassive black hole weighing up to a billion times the sun’s mass and roughly the size of our planetary system. As matter falls toward the black hole, some particles race away at nearly the speed of light along a pair of jets pointed in opposite directions. What makes a blazar so bright is that one of these particle jets happens to be aimed almost straight at us.

    “This flare is the most dynamic outburst Fermi has seen in its seven years of operation, becoming 10 times brighter overnight,” said Elizabeth Hays, a Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Astronomers think some change within the jet is likely responsible for the flare, but they don’t know what it is.

    The brightest persistent source in the gamma-ray sky is the Vela pulsar, which is about 1,000 light-years away.

    2
    The Vela Pulsar and its surrounding pulsar wind nebula
    NASA/CXC/PSU/G.Pavlov et al.
    6 July 2003

    3C 279 is millions of times farther off, but during this flare it became four times brighter than Vela. This corresponds to a tremendous energy release, and one that cannot be sustained for long. The galaxy dimmed to normal gamma-ray levels by June 18.

    The rapid fading is why astronomers rush to collect data as soon as they detect a blazar flare. “Our priority is to make observations while the object is still bright,” said Masaaki Hayashida, a Fermi team member at the University of Tokyo’s Institute for Cosmic Ray Research. “Once it’s over, we can start trying to understand the mechanisms powering it.”

    The Italian Space Agency’s AGILE gamma-ray satellite first reported the flare, followed by Fermi.
    Rapid follow-up observations were made by NASA’s Swift satellite and the European Space Agency’s INTEGRAL spacecraft, which just happened to be looking in the right direction, along with optical and radio telescopes on the ground.

    Italian Space Agency AGILE Spacecraft
    ISA AGILE

    NASA SWIFT Telescope
    NASA/Swift

    ESA Integral
    ESA/Integral

    3C 279 holds a special place in the history of gamma-ray astronomy. During a flare in 1991 detected by the EGRET instrument on NASA’s then recently launched Compton Gamma Ray Observatory (CGRO), which operated until 2000, the galaxy set the record for the most distant and luminous gamma-ray source known at the time. “Although we didn’t expect to find the galaxy so bright, we soon had a much greater surprise,” recalled Robert Hartman, who led the first gamma-ray study of 3C 279 with CGRO and is now a member of the Fermi team at Goddard. “Its brightness varied substantially, becoming four times brighter within 10 days.”

    The June 14 outburst rapidly brightened in less than a day and peaked on June 16, producing a gamma-ray flare 10 times brighter than the 1991 event. These rapid variations convey information about the size of the emitting region, which cannot be larger than the distance light can travel during the flare.

    Mid-June proved to be an intense period for the Fermi team. As the satellite’s Large Area Telescope studied 3C 279, its Gamma-ray Burst Monitor became the busiest it has ever been since the start of the mission. The instrument picked up a series of eruptions on the sun, which is unusual in itself, as well as multiple outbursts from V404 Cygni, a binary system containing a black hole that erupts every few decades.

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

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 3:18 pm on June 24, 2015 Permalink | Reply
    Tags: , , , NASA Fermi,   

    From Symmetry: “Seeing in gamma rays” 

    Symmetry

    June 24, 2015
    Glenn Roberts Jr.

    1
    Courtesy of Fermi LAT collaboration

    The Fermi Gamma-ray Space Telescope creates maps of the gamma-ray sky.

    Maps from the Fermi Gamma-ray Space Telescope literally show the universe in a different light.

    NASA Fermi Telescope
    Fermi

    Fermi’s Large Area Telescope (LAT) has been watching the universe at a broad range of gamma-ray energies for more than seven years.

    Gamma rays are the highest-energy form of light in the cosmos. They come from jets of high-energy particles accelerated near supermassive black holes at the centers of galaxies, shock waves around exploded stars, and the intense magnetic fields of fast-spinning collapsed stars. On Earth, gamma rays are produced by nuclear reactors, lightning and the decay of radioactive elements.

    From low-Earth orbit, the Fermi Gamma-ray Space Telescope scans the entire sky for gamma rays every three hours. It captures new and recurring sources of gamma rays at different energies, and it can be diverted from its usual course to fix on explosive events known as gamma-ray bursts.

    Combining data collected over years, the LAT collaboration periodically creates gamma-ray maps of the universe. These colored maps plot the universe’s most extreme events and high-energy objects.

    The all-sky maps typically portray the universe as an ellipse that shows the entire sky at once, as viewed from Earth. On the maps, the brightest gamma-ray light is shown in yellow and progressively dimmer gamma-ray light is shown in red, blue, and black. These are false colors, though; gamma-rays are invisible.

    The maps are oriented with the center of the Milky Way at their center and the plane of our galaxy oriented horizontally across the middle. The plane of the Milky Way is bright in gamma rays. Above and below the bright band, much of the gamma-ray light comes from outside of our galaxy.

    “What you see in gamma rays is not so predictable,” says Elliott Bloom, a SLAC National Accelerator Laboratory professor and member of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) who is part of a scientific collaboration supporting Fermi’s principal instrument, the Large Area Telescope.

    Teams of researchers have identified mysterious, massive “bubbles” blooming 30,000 light-years outward from our galaxy’s center, for example, with most features appearing only at gamma-ray wavelengths.

    Scientists create several versions of the Fermi sky maps. Some of them focus only on a specific energy range, says Eric Charles, another member of the Fermi collaboration who is also a KIPAC scientist.

    “You learn a lot by correlating things in different energy ‘bins,’” he says. “If you look at another map and see completely different things, then there may be these different processes. What becomes useful is at different wavelengths you can make comparisons and correlate things.”

    But sometimes what you need is the big picture, says Seth Digel, a SLAC senior staff scientist and a member of KIPAC and the Fermi team. “There are some aspects you can only study with maps, such as looking at the extended gamma-ray emissions—not just the point sources, but regions of the sky that are glowing in gamma rays for different reasons.”

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 9:23 am on June 12, 2015 Permalink | Reply
    Tags: , , , , NASA Fermi   

    From FNAL- “Frontier Science Result: Fermi Gamma-Ray Space Telescope” 

    FNAL Home

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    June 12, 2015
    Dan Hooper

    NASA Fermi Telescope
    Fermi Gamma Ray Telescope

    2
    A team of astrophysicists is looking for dark matter in the form of subhalos. These clumps of dark matter within the Milky Way are predicted to produce a distinctive gamma-ray signal. Image courtesy of The Aquarius Project

    In addition to teaching us about pulsars, cosmic rays and supermassive black holes, the Fermi Gamma Ray Space Telescope is one of the world’s premier dark matter experiments. In many models, the interactions of dark matter particles can create energetic photons, known as gamma rays. Fermi provides us with our most sensitive view of the gamma-ray sky and is able to test many of our most promising theories of dark matter.

    Over the past several years, my collaborators and I have published a series of papers describing an excess of gamma rays from the region surrounding the center of the Milky Way. After many long discussions, arguments and debates, the majority of the gamma-ray astrophysics community seems to have reached a consensus that this excess is real and is in need of an explanation. One exciting possibility is that these gamma rays could be produced by dark matter particles. But even though this signal looks very much like what we expected from dark matter, we can’t entirely rule out other explanations, such as a series of recent outbursts of cosmic rays or some unknown population of faint gamma-ray sources.

    One way to potentially confirm a dark matter origin for this excess would be to observe the same spectrum of gamma rays from otherwise invisible clumps of dark matter — known as subhalos — elsewhere in the sky. In fact, if the gamma rays from the Galactic Center do come from dark matter particles, we estimate that Fermi should be able to detect a handful of these subhalos as bright gamma-ray sources. The challenge is that Fermi has detected hundreds of bright, unidentified sources, the vast majority of which are not related to dark matter. This large haystack of sources makes it hard to find the dark matter subhalos that are the needles we are looking for.

    But in one important respect, dark matter subhalos should look different from other kinds of gamma-ray sources: They should be slightly extended or “puffy.” My collaborators (Bridget Bertoni of the University of Washington and Tim Linden of the University of Chicago) and I have recently found evidence that some of Fermi’s unidentified sources are in fact extended, making them seem more likely to be dark matter subhalos. We continue to scrutinize the data, and although we’re not prepared to claim discovery yet, we are very excited that this new information might make it possible to independently test — and maybe even confirm — a dark matter origin for Fermi’s Galactic Center gamma-ray excess.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Fermilab Campus

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

     
  • richardmitnick 8:17 am on May 14, 2015 Permalink | Reply
    Tags: , , NASA Fermi,   

    From New Scientist: “Found: giant spirals in space that could explain our existence” 

    NewScientist

    New Scientist

    14 May 2015
    Michael Slezak

    Giant magnetic spirals in the sky could explain why there is something rather than nothing in the universe, according to an analysis of data from NASA’s Fermi space telescope.

    NASA Fermi Telescope

    Our best theories of physics imply we shouldn’t be here. The Big Bang ought to have produced equal amounts of matter and antimatter particles, which would almost immediately annihilate each other, leaving nothing but light.

    So the reality that we are here – and there seems to be very little antimatter around – is one of the biggest unsolved mysteries in physics.

    Monopole monopoly

    In 2001, Tanmay Vachaspati from Arizona State University offered a purely theoretical solution. Even if matter and antimatter were created in equal amounts, he suggested that as they annihilated each other, they would have briefly created monopoles and antimonopoles, hypothetical particles with just one magnetic pole, north or south.

    As the monopoles and antimonopoles in turn annihilated each other, they would produce matter and antimatter. But because of a quirk in nature called CP violation, that process would be biased towards matter, leaving the matter-filled world we see today.

    If that happened, Vachaspati showed that there should be a sign of it today: twisted magnetic fields permeating the universe – a fossil of the magnetic monopoles that briefly dominated. And he showed they should look like left-handed screws rather than right-handed screws.

    So Vachaspati and his colleagues went looking for them in data from NASA’s Fermi Gamma ray Space Telescope. As gamma rays shoot through the cosmos, they should be bent by any magnetic field they pass through, so if there are helical magnetic fields permeating the universe, that should leave a visible mark on those gamma rays.

    All of a twist

    Lo and behold, that’s just what they found – well, maybe. “What we found is consistent with them all being left-handed,” says Vachaspati. “But we can’t be sure.” He says there’s less than a one per cent chance that what they see in the Fermi data happened by chance. “That’s being conservative,” he says.

    They also found that the twists in the field are a bit bigger than they predicted. “So there is some mystery there,” says Vachaspati. He says more data from Fermi, which is expected this year, will help narrow down the odds.

    Nicole Bell from the University of Melbourne in Australia warns that magnetic fields could have been caused in other ways, including from inflation. What’s more, for CP-violation to provide enough matter in the universe you usually need “new physics” – stuff beyond the standard model of particle physics – which hasn’t been confirmed experimentally yet. “But it is a very interesting idea,” she says.

    Journal reference: Monthly Notices of the Royal Astronomical Society, DOI: 10.1093/mnras/stv308

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 10:38 am on February 5, 2015 Permalink | Reply
    Tags: , , NASA Fermi,   

    From Space.com: “Mystery of the Universe’s Gamma-Ray Glow Solved” 

    space-dot-com logo

    SPACE.com

    February 05, 2015
    Calla Cofield

    1
    Five years of data from the Fermi Gamma-ray Space Telescope paint a picture of the universe in gamma-rays. Scientists with Fermi think the flux of gamma-rays can be explained by known sources.
    Credit: gamma ray sky, gamma ray universe, fermi telescope, blazars, radio galaxies, gamma ray emitters, gamma ray sources, milky way gamma rays

    The steady glow of high-energy gamma-ray light that spreads across the cosmos has puzzled astronomers for decades. One team of researchers thinks it has the best explanation yet for the source of this strange emission.

    After observing the universe with NASA’s Fermi Gamma-ray Space Telescope for six years, scientists with the mission say the majority of the gamma-ray glow they have seen can be explained by objects already known to science. If there are any as-yet unknown sources out there, their contribution to the glow would be very small, scientists say.

    NASA Fermi Telescope
    NASA/Fermi

    “We have a very plausible story. We’re not 100 percent confident that this is the final answer, but it really constrains what other exotic possibilities could be out there,” said Keith Bechtol, a postdoctoral researcher at the University of Chicago and a member of the Fermi collaboration who worked on the analysis.

    4
    Galactic Haze Seen by Planck and Galactic ‘Bubbles’ Seen by Fermi
    Credit: ESA/Planck Collaboration (microwave); NASA/DOE/Fermi LAT/D. Finkbeiner et al. (gamma rays)
    This all-sky image shows the distribution of the galactic haze seen by ESA’s Planck mission at microwave frequencies superimposed over the high-energy sky, as seen by NASA’s Fermi Gamma-ray Space Telescope. Image released February 13, 2012.

    ESA Planck
    ESA/Planck

    5
    W44 Supernova Remnant
    Credit: NASA/DOE/Fermi LAT Collaboration, ROSAT, JPL-Caltech, and NRAO/AUI
    Fermi’s LAT mapped GeV-gamma-ray emission (magenta) from the W44 supernova remnant. The features clearly align with filaments detectable in other wavelengths. This composite merges X-rays (blue) from the Germany-led ROSAT mission, infrared (red) from NASA’s Spitzer Space Telescope, and radio (orange) from the NRAO’s Very Large Array near Socorro, N.M.

    NASA ROSAT satellite
    ROSAT

    NASA Spitzer Telescope
    NASA/Spitzer

    NRAO VLA
    NRAO/VLA

    Fermi: a gamma-ray gumshoe

    NASA’s Fermi Gamma-ray Space Telescope snaps pictures of the entire observable universe — from end to end — in gamma-rays, which are some of the highest-energy photons in nature.

    While that wide view of the universe is useful, it can make it a challenge to pinpoint the exact sources of these gamma-rays. Instead, Fermi sees a diffuse glow coming from the universe. This glow is technically known as the extragalactic gamma ray background, or the EGB. Previous gamma-ray telescopes have also seen this light that fills the background of the cosmos.

    “We’ve known about this gamma-ray background since the late 1960s,” Bechtol said. “It’s a very-long-standing mystery, and each generation of gamma-ray telescopes has given us a little more information.”

    With help from other telescopes, the Fermi telescope can identify where some of this high-energy background light is coming from. There are very energetic galaxies called blazars, for example, that give off a high flux of gamma-rays. The Energetic Gamma Ray Experiment Telescope (EGRET), which preceded Fermi, broke records by detecting some 300 gamma-ray sources. So far, the Fermi telescope has identified more than 3,000 sources.

    NASA Energetic Gamma Ray Telescope

    But 3,000 is only a drop in the ocean of gamma-ray sources in the entire universe, scientists say.

    “We think every galaxy is producing gamma-rays at some level,” Bechtol said. “The vast majority are too faint to be seen individually and instead their collective emission is blurred together.” (Many galaxies radiate high levels of optical light, and can be seen by telescopes like the Hubble. But their gamma-ray emission is too faint to be detected.)

    “It’s frustrating not to know the answer, but the fact that there’s a mystery — I think that’s what attracted a lot of us to this problem,” Bechtol said. “At least for me, I like being on the edge of that discovery space where there’s still blank parts on the map.”

    Cracking the mystery

    The Fermi telescope can’t see most of the objects that radiate gamma-ray light, so the scientists have to try to estimate how many gamma-ray objects are out there.

    In an analysis first made public in September 2014, members of the Fermi collaboration took the known sources of gamma-rays and added them together with models that predicted the frequency and location of unseen sources. The scientists calculated how much gamma-ray light both the detected and modeled sources would produce together.

    This calculated output of gamma rays matches closely with the actual gamma ray-background that Fermi observes — the entire EGB.

    The final estimate shows that roughly 50 percent of the gamma-ray background comes from extremely energetic galaxies known as blazars. Ten to 30 percent of the gamma ray background emanates from star-forming galaxies like the Milky Way, which can collectively contain many smaller gamma-ray sources, like supernovas. Another 20 percent is from radio galaxies, which are blazars, but are pointed away from the Earth, and thus cannot be seen as easily by Fermi.

    “There could definitely be new gamma-ray sources out there,” Bechtol said. “It’s just that their total contribution would have to be relatively small.”

    It’s also possible that dark matter — the mysterious material that makes up 80 percent of all the matter in the universe — is producing gamma-rays, and the Fermi results may help scientists figure out what kind of particle (or particles) make up dark matter.

    Two large uncertainties remain in Fermi’s estimation. First, it is difficult to measure the gamma-ray glow of the universe to begin with, and Bechtol said he and his collaborators put a lot of time into improving that measurement.

    Second, the scientists are making estimates about objects they cannot directly observe, most of which are located beyond the Milky Way galaxy (or extragalactic).

    “When [scientists] first discovered the gamma-ray background, it was largely a mystery as to what created it,” Bechtol said. “And now it seems like everything is fitting together very well. Right now, the simplest explanation involving known astrophysical sources seems to be doing just fine.”

    6
    The Fermi Large Area Telescope has spotted highly energetic ejections of gamma-rays throughout the universe. Scientists with Fermi believe known gamma-ray sources can account for the overall gamma-ray flux in the universe, but they say there is still room for surprises.
    Credit: NASA/DOE/Fermi LAT Collaboration

    Light from back in time

    Fermi’s success at decoding the gamma-ray background had depended largely on its increased sensitivity to gamma-rays and its detection of more gamma-ray sources than previous telescopes. In addition, Fermi scientists have worked to gain a better understanding of how gamma-ray emissions have changed throughout the history of the universe. This is valuable because when Fermi looks at sources of gamma-rays, it is actually looking into the past.

    Light travels at a finite speed — the light from the sun takes 8 minutes to reach Earth, which means humans actually see the sun as it was 8 minutes ago. By the same logic, objects that are billions of light-years away from Earth are seen by Fermi as they were billions of years ago.

    “We’re literally measuring the light output over the history of the universe, and for me, that’s what makes this exciting,” Bechtol said. “We’re seeing all different time periods in the universe at the same time. All of the light from all those different periods is added together to form the gamma ray background.”

    Having a historical perspective makes a big difference for Fermi because the cosmic output of gamma-rays has likely been different at various times throughout the last 13 billion years. For example, the universe has seen periods when the population of blazars exploded and other times when the population growth slowed down. They also need to understand precisely how far away those blazars are, in order to accurately measure how long ago these bright sources burned.

    The Fermi scientists have solved a long-standing puzzle, but Bechtol said there are still other mysteries in the gamma-ray universe. There are other gamma-ray telescopes that can detect even higher-energy gamma-rays than Fermi, and it’s possible that in those energy ranges, there are sources of gamma-rays that scientists don’t know about yet.

    “We think this [result] is converging on the final answer, but history has shown us that, sometimes, there’s more to the story,” Bechtol said. “I certainly think that, as we start to look at higher energies […], there will start to be some surprises.”

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 9:45 am on January 1, 2015 Permalink | Reply
    Tags: , , NASA Fermi   

    From NASA Science News: “Terrestrial Gamma-ray Flashes, More Common Than Previously Thought?” 

    NASA Science Science News

    Dec 31, 2014
    Dr. Tony Phillips

    Each day, thunderstorms around the world produce about a thousand quick bursts of gamma rays, some of the highest-energy light naturally found on Earth. By merging records of events seen by NASA’s Fermi Gamma-ray Space Telescope with data from ground-based radar and lightning detectors, scientists have completed the most detailed analysis to date of the types of thunderstorms involved.

    NASA Fermi Telescope
    NASA/Fermi

    “Remarkably, we have found that any thunderstorm can produce gamma rays, even those that appear to be so weak a meteorologist wouldn’t look twice at them,” said Themis Chronis, who led the research at the University of Alabama in Huntsville (UAH).


    New research merging Fermi data with information from ground-based radar and lightning networks shows that terrestrial gamma-ray flashes arise from an unexpected diversity of storms and may be more common than currently thought. Play video

    The outbursts, called terrestrial gamma-ray flashes (TGFs), were discovered in 1992 by NASA’s Compton Gamma-Ray Observatory, which operated until 2000. TGFs occur unpredictably and fleetingly, with durations less than a thousandth of a second, and remain poorly understood.

    NASA Compton Gamma Ray Observatory

    In late 2012, Fermi scientists employed new techniques that effectively upgraded the satellite’s Gamma-ray Burst Monitor (GBM), making it 10 times more sensitive to TGFs and allowing it to record weak events that were overlooked before.

    “As a result of our enhanced discovery rate, we were able to show that most TGFs also generate strong bursts of radio waves like those produced by lightning,” said Michael Briggs, assistant director of the Center for Space Plasma and Aeronomic Research at UAH and a member of the GBM team.

    Previously, TGF positions could be roughly estimated based on Fermi’s location at the time of the event. The GBM can detect flashes within about 500 miles (800 kilometers), but this is too imprecise to definitively associate a TGF with a specific storm.

    Ground-based lightning networks use radio data to pin down strike locations. The discovery of similar signals from TGFs meant that scientists could use the networks to determine which storms produce gamma-ray flashes, opening the door to a deeper understanding of the meteorology powering these extreme events.

    Chronis, Briggs and their colleagues sifted through 2,279 TGFs detected by Fermi’s GBM to derive a sample of nearly 900 events accurately located by the Total Lightning Network operated by Earth Networks in Germantown, Maryland, and the World Wide Lightning Location Network, a research collaboration run by the University of Washington in Seattle. These systems can pinpoint the location of lightning discharges — and the corresponding signals from TGFs — to within 6 miles (10 km) anywhere on the globe.

    From this group, the team identified 24 TGFs that occurred within areas covered by Next Generation Weather Radar (NEXRAD) sites in Florida, Louisiana, Texas, Puerto Rico and Guam. For eight of these storms, the researchers obtained additional information about atmospheric conditions through sensor data collected by the Department of Atmospheric Science at the University of Wyoming in Laramie.

    “All told, this study is our best look yet at TGF-producing storms, and it shows convincingly that storm intensity is not the key,” said Chronis, who will present the findings Wed., Dec. 17, in an invited talk at the American Geophysical Union meeting in San Francisco. A paper describing the research has been submitted to the Bulletin of the American Meteorological Society.

    Scientists suspect that TGFs arise from strong electric fields near the tops of thunderstorms. Updrafts and downdrafts within the storms force rain, snow and ice to collide and acquire electrical charge. Usually, positive charge accumulates in the upper part of the storm and negative charge accumulates below. When the storm’s electrical field becomes so strong it breaks down the insulating properties of air, a lightning discharge occurs.

    Under the right conditions, the upper part of an intracloud lightning bolt disrupts the storm’s electric field in such a way that an avalanche of electrons surges upward at high speed. When these fast-moving electrons are deflected by air molecules, they emit gamma rays and create a TGF.

    About 75 percent of lightning stays within the storm, and about 2,000 of these intracloud discharges occur for each TGF Fermi detects.

    The new study confirms previous findings indicating that TGFs tend to occur near the highest parts of a thunderstorm, between about 7 and 9 miles (11 to 14 kilometers) high. “We suspect this isn’t the full story,” explained Briggs. “Lightning often occurs at lower altitudes and TGFs probably do too, but traveling the greater depth of air weakens the gamma rays so much the GBM can’t detect them.”

    Based on current Fermi statistics, scientists estimate that some 1,100 TGFs occur each day, but the number may be much higher if low-altitude flashes are being missed.

    While it is too early to draw conclusions, Chronis notes, there are a few hints that gamma-ray flashes may prefer storm areas where updrafts have weakened and the aging storm has become less organized. “Part of our ongoing research is to track these storms with NEXRAD radar to determine if we can relate TGFs to the thunderstorm life cycle,” he said.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    NASA leads the nation on a great journey of discovery, seeking new knowledge and understanding of our planet Earth, our Sun and solar system, and the universe out to its farthest reaches and back to its earliest moments of existence. NASA’s Science Mission Directorate (SMD) and the nation’s science community use space observatories to conduct scientific studies of the Earth from space to visit and return samples from other bodies in the solar system, and to peer out into our Galaxy and beyond. NASA’s science program seeks answers to profound questions that touch us all:

    This is NASA’s science vision: using the vantage point of space to achieve with the science community and our partners a deep scientific understanding of our planet, other planets and solar system bodies, the interplanetary environment, the Sun and its effects on the solar system, and the universe beyond. In so doing, we lay the intellectual foundation for the robotic and human expeditions of the future while meeting today’s needs for scientific information to address national concerns, such as climate change and space weather. At every step we share the journey of scientific exploration with the public and partner with others to substantially improve science, technology, engineering and mathematics (STEM) education nationwide.

    NASA

     
  • richardmitnick 9:45 pm on July 31, 2014 Permalink | Reply
    Tags: , , , , NASA Fermi,   

    From SLAC Lab: “Despite Extensive Analysis, Fermi Bubbles Defy Explanation” 


    SLAC Lab

    July 31, 2014

    Scientists from Stanford and the Department of Energy’s SLAC National Accelerator Laboratory have analyzed more than four years of data from NASA’s Fermi Gamma-ray Space Telescope, along with data from other experiments, to create the most detailed portrait yet of two towering bubbles that stretch tens of thousands of light-years above and below our galaxy.

    https://www6.slac.stanford.edu/sites/www6.slac.stanford.edu/files/styles/lightbox_large_image/public/images/Fermi_bubbles-ST.jpg
    This artist’s representation shows the Fermi bubbles towering above and below the galaxy. (NASA’s Goddard Space Flight Center)

    NASA Fermi Telescope
    NASA/Fermi

    The bubbles, which shine most brightly in energetic gamma rays, were discovered almost four years ago by a team of Harvard astrophysicists led by Douglas Finkbeiner who combed through data from Fermi’s main instrument, the Large Area Telescope.

    NASA Fermi LAT Large Area Telescope
    NASA/Fermi LAT

    The new portrait, described in a paper that has been accepted for publication in The Astrophysical Journal, reveals several puzzling features, said Dmitry Malyshev, a postdoctoral researcher at the Kavli Institute for Particle Astrophysics and Cosmology who co-led on the analysis.

    For example, the outlines of the bubbles are quite sharp, and the bubbles themselves glow in nearly uniform gamma rays over their colossal surfaces, like two 30,000-light-year-tall incandescent bulbs screwed into the center of the galaxy.

    Their size is another puzzle. The farthest reaches of the Fermi bubbles boast some of the highest energy gamma rays, but there’s no discernable cause for them that far from the galaxy.

    Finally, although the parts of the bubbles closest to the galactic plane shine in microwaves as well as gamma rays, about two-thirds of the way out the microwaves fade and only gamma rays are detectable. Not only is this different from other galactic bubbles, but it makes the researchers’ work that much more challenging, said Malyshev’s co-lead, KIPAC postdoctoral researcher Anna Franckowiak.

    two
    KIPAC researchers Dmitry Malyshev (left) and Anna Franckowiak with the magazine issues that contain the articles about the Fermi bubbles they co-authored for the general public. Malyshev’s is in the July 2014 issue of Scientific American, while Franckowiak’s article is in the July 2014 issue of Physics Today. (SLAC National Accelerator Laboratory)

    “Since the Fermi bubbles have no known counterparts in other wavelengths in areas high above the galactic plane, all we have to go on for clues are the gamma rays themselves,” she said.

    What Blew The Bubbles?

    Soon after the initial discovery theorists jumped in, offering several explanations for the bubbles’ origins. For example, they could have been created by huge jets of accelerated matter blasting out from the supermassive black hole at the center of our galaxy. Or they could have been formed by a population of giant stars, born from the plentiful gas surrounding the black hole, all exploding as supernovae at roughly the same time.

    “There are several models that explain them, but none of the models is perfect,” Malyshev said. “The bubbles are rather mysterious.”

    Creating the portrait wasn’t easy.

    “It’s very tricky to model,” said Franckowiak. “We had to remove all the foreground gamma-ray emissions from the data before we could clearly see the bubbles.”

    From the vantage point of most Earth-bound telescopes, all but the highest-energy gamma rays are completely screened out by our atmosphere. It wasn’t until the era of orbiting gamma-ray observatories like Fermi that scientists discovered how common extra-terrestrial gamma rays really are. Pulsars, supermassive black holes in other galaxies and supernovae are all gamma rays point sources, like distant stars are point sources of visible light, and all those gamma rays had to be scrubbed from the Fermi data. Hardest to remove were the galactic diffuse emissions, a gamma ray fog that fills the galaxy from cosmic rays interacting with interstellar particles.

    “Subtracting all those contributions didn’t subtract the bubbles,” Franckowiak said. “The bubbles do exist and their properties are robust.” In other words, the bubbles don’t disappear when other gamma-ray sources are pulled out of the Fermi data – in fact, they stand out quite clearly.

    Franckowiak says more data is necessary before they can narrow down the origin of the bubbles any further.

    “What would be very interesting would be to get a better view of them closer to the galactic center,” she said, “but the galactic gamma ray emissions are so bright we’d need to get a lot better at being able to subtract them.”

    Fermi is continuing to gather the data Franckowiak wants, but for now, both researchers said, there are a lot of open questions.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
    i1


    ScienceSprings is powered by MAINGEAR computers

     
  • richardmitnick 4:10 pm on July 31, 2014 Permalink | Reply
    Tags: , , , , , NASA Fermi   

    From NASA/Fermi: “NASA’s Fermi Space Telescope Reveals New Source of Gamma Rays” 

    NASA Fermi

    July 31, 2014
    No Writer Credit

    Observations by NASA’s Fermi Gamma-ray Space Telescope of several stellar eruptions, called novae, firmly establish these relatively common outbursts almost always produce gamma rays, the most energetic form of light.

    novae
    These images show Fermi data centered on each of the four gamma-ray novae observed by the LAT. Colors indicate the number of detected gamma rays with energies greater than 100 million electron volts (blue indicates lowest, yellow highest). Image Credit: NASA/DOE/Fermi LAT Collaboration

    “There’s a saying that one is a fluke, two is a coincidence, and three is a class, and we’re now at four novae and counting with Fermi,” said Teddy Cheung, an astrophysicist at the Naval Research Laboratory in Washington, and the lead author of a paper reporting the findings in the Aug. 1 edition of the journal Science.

    A nova is a sudden, short-lived brightening of an otherwise inconspicuous star caused by a thermonuclear explosion on the surface of a white dwarf, a compact star not much larger than Earth. Each nova explosion releases up to 100,000 times the annual energy output of our sun. Prior to Fermi, no one suspected these outbursts were capable of producing high-energy gamma rays, emission with energy levels millions of times greater than visible light and usually associated with far more powerful cosmic blasts.

    Fermi’s Large Area Telescope (LAT) scored its first nova detection, dubbed V407 Cygni, in March 2010. The outburst came from a rare type of star system in which a white dwarf interacts with a red giant, a star more than a hundred times the size of our sun. Other members of the same unusual class of stellar system have been observed “going nova” every few decades.

    NASA Fermi LAT Large Area Telescope
    NASA/Fermi LAT

    image
    The white dwarf star in V407 Cygni, shown here in an artist’s concept, went nova in 2010. Scientists think the outburst primarily emitted gamma rays (magenta) as the blast wave plowed through the gas-rich environment near the system’s red giant star. Image Credit: NASA’s Goddard Space Flight Center/S. Wiessinger

    In 2012 and 2013, the LAT detected three so-called classical novae which occur in more common binaries where a white dwarf and a sun-like star orbit each other every few hours.

    “We initially thought of V407 Cygni as a special case because the red giant’s atmosphere is essentially leaking into space, producing a gaseous environment that interacts with the explosion’s blast wave,” said co-author Steven Shore, a professor of astrophysics at the University of Pisa in Italy. “But this can’t explain more recent Fermi detections because none of those systems possess red giants.”

    Fermi detected the classical novae V339 Delphini in August 2013 and V1324 Scorpii in June 2012, following their discovery in visible light. In addition, on June 22, 2012, the LAT discovered a transient gamma-ray source about 20 degrees from the sun. More than a month later, when the sun had moved farther away, astronomers looking in visible light discovered a fading nova from V959 Monocerotis at the same position.

    Astronomers estimate that between 20 and 50 novae occur each year in our galaxy. Most go undetected, their visible light obscured by intervening dust and their gamma rays dimmed by distance. All of the gamma-ray novae found so far lie between 9,000 and 15,000 light-years away, relatively nearby given the size of our galaxy.

    Novae occur because a stream of gas flowing from the companion star piles up into a layer on the white dwarf’s surface. Over time — tens of thousands of years, in the case of classical novae, and several decades for a system like V407 Cygni — this deepening layer reaches a flash point. Its hydrogen begins to undergo nuclear fusion, triggering a runaway reaction that detonates the accumulated gas. The white dwarf itself remains intact.

    shock
    Novae typically originate in binary systems containing sun-like stars, as shown in this artist’s rendering. A nova in a system like this likely produces gamma rays (magenta) through collisions among multiple shock waves in the rapidly expanding shell of debris. Image Credit: NASA’s Goddard Space Flight Center/S. Wiessinger

    One explanation for the gamma-ray emission is that the blast creates multiple shock waves that expand into space at slightly different speeds. Faster shocks could interact with slower ones, accelerating particles to near the speed of light. These particles ultimately could produce gamma rays.

    “This colliding-shock process must also have been at work in V407 Cygni, but there is no clear evidence for it,” said co-author Pierre Jean, a professor of astrophysics at the University of Toulouse in France. This is likely because gamma rays emitted through this process were overwhelmed by those produced as the shock wave interacted with the red giant and its surroundings, the scientists conclude.

    See the full article here.

    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.


    ScienceSprings is powered by MAINGEAR computers

     
  • richardmitnick 6:59 pm on July 22, 2014 Permalink | Reply
    Tags: , , , NASA Fermi   

    From NASA/Fermi: “NASA’s Fermi Finds A ‘Transformer’ Pulsar” 

    NASA Fermi

    July 22, 2014
    Francis Reddy, NASA’s Goddard Space Flight Center, Greenbelt, Maryland

    In late June 2013, an exceptional binary containing a rapidly spinning neutron star underwent a dramatic change in behavior never before observed. The pulsar’s radio beacon vanished, while at the same time the system brightened fivefold in gamma rays, the most powerful form of light, according to measurements by NASA’s Fermi Gamma-ray Space Telescope.

    split
    These artist’s renderings show one model of pulsar J1023 before (top) and after (bottom) its radio beacon (green) vanished. Normally, the pulsar’s wind staves off the companion’s gas stream. When the stream surges, an accretion disk forms and gamma-ray particle jets (magenta) obscure the radio beam. Image Credit: NASA’s Goddard Space Flight Center

    “It’s almost as if someone flipped a switch, morphing the system from a lower-energy state to a higher-energy one,” said Benjamin Stappers, an astrophysicist at the University of Manchester, England, who led an international effort to understand this striking transformation. “The change appears to reflect an erratic interaction between the pulsar and its companion, one that allows us an opportunity to explore a rare transitional phase in the life of this binary.”

    A binary consists of two stars orbiting around their common center of mass. This system, known as AY Sextantis, is located about 4,400 light-years away in the constellation Sextans. It pairs a 1.7-millisecond pulsar named PSR J1023+0038 — J1023 for short — with a star containing about one-fifth the mass of the sun. The stars complete an orbit in only 4.8 hours, which places them so close together that the pulsar will gradually evaporate its companion.

    When a massive star collapses and explodes as a supernova, its crushed core may survive as a compact remnant called a neutron star or pulsar, an object squeezing more mass than the sun’s into a sphere no larger than Washington, D.C. Young isolated neutron stars rotate tens of times each second and generate beams of radio, visible light, X-rays and gamma rays that astronomers observe as pulses whenever the beams sweep past Earth. Pulsars also generate powerful outflows, or “winds,” of high-energy particles moving near the speed of light. The power for all this comes from the pulsar’s rapidly spinning magnetic field, and over time, as the pulsars wind down, these emissions fade.

    More than 30 years ago, astronomers discovered another type of pulsar revolving in 10 milliseconds or less, reaching rotational speeds up to 43,000 rpm. While young pulsars usually appear in isolation, more than half of millisecond pulsars occur in binary systems, which suggested an explanation for their rapid spin.

    “Astronomers have long suspected millisecond pulsars were spun up through the transfer and accumulation of matter from their companion stars, so we often refer to them as recycled pulsars,” explained Anne Archibald, a postdoctoral researcher at the Netherlands Institute for Radio Astronomy (ASTRON) in Dwingeloo who discovered J1023 in 2007.

    During the initial mass-transfer stage, the system would qualify as a low-mass X-ray binary, with a slower-spinning neutron star emitting X-ray pulses as hot gas raced toward its surface. A billion years later, when the flow of matter comes to a halt, the system would be classified as a spun-up millisecond pulsar with radio emissions powered by a rapidly rotating magnetic field.

    To better understand J1023’s spin and orbital evolution, the system was regularly monitored in radio using the Lovell Telescope in the United Kingdom and the Westerbork Synthesis Radio Telescope in the Netherlands. These observations revealed that the pulsar’s radio signal had turned off and prompted the search for an associated change in its gamma-ray properties.

    Lovell
    Lovell at Jodrell Bank

    westerbrook
    Westerbork

    A few months before this, astronomers found a much more distant system that flipped between radio and X-ray states in a matter of weeks. Located in M28, a globular star cluster about 19,000 light-years away, a pulsar known as PSR J1824-2452I underwent an X-ray outburst in March and April 2013. As the X-ray emission dimmed in early May, the pulsar’s radio beam emerged.

    While J1023 reached much higher energies and is considerably closer, both binaries are otherwise quite similar. What’s happening, astronomers say, are the last sputtering throes of the spin-up process for these pulsars.

    In J1023, the stars are close enough that a stream of gas flows from the sun-like star toward the pulsar. The pulsar’s rapid rotation and intense magnetic field are responsible for both the radio beam and its powerful pulsar wind. When the radio beam is detectable, the pulsar wind holds back the companion’s gas stream, preventing it from approaching too closely. But now and then the stream surges, pushing its way closer to the pulsar and establishing an accretion disk.

    Gas in the disk becomes compressed and heated, reaching temperatures hot enough to emit X-rays. Next, material along the inner edge of the disk quickly loses orbital energy and descends toward the pulsar. When it falls to an altitude of about 50 miles (80 km), processes involved in creating the radio beam are either shut down or, more likely, obscured.

    The inner edge of the disk probably fluctuates considerably at this altitude. Some of it may become accelerated outward at nearly the speed of light, forming dual particle jets firing in opposite directions — a phenomenon more typically associated with accreting black holes. Shock waves within and along the periphery of these jets are a likely source of the bright gamma-ray emission detected by Fermi.

    The findings were published in the July 20 edition of The Astrophysical Journal. The team reports that J1023 is the first example of a transient, compact, low-mass gamma-ray binary ever seen. The researchers anticipate that the system will serve as a unique laboratory for understanding how millisecond pulsars form and for studying the details of how accretion takes place on neutron stars.

    “So far, Fermi has increased the number of known gamma-ray pulsars by about 20 times and doubled the number of millisecond pulsars within in our galaxy,” said Julie McEnery, the project scientist for the mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Fermi continues to be an amazing engine for pulsar discoveries.”

    See the full article here.

    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.


    ScienceSprings is powered by MAINGEAR computers

     
  • richardmitnick 4:04 am on June 4, 2014 Permalink | Reply
    Tags: , , , , NASA Fermi   

    From NASA/FERMI: “Black Hole ‘Batteries’ Keep Blazars Going and Going” 


    Fermi

    June 3, 2014
    No Writer Credit

    Astronomers studying two classes of black-hole-powered galaxies monitored by NASA’s Fermi Gamma-ray Space Telescope have found evidence that they represent different sides of the same cosmic coin. By unraveling how these objects, called blazars, are distributed throughout the universe, the scientists suggest that apparently distinctive properties defining each class more likely reflect a change in the way the galaxies extract energy from their central black holes.

    blazar
    Typical look of a blazar

    “We can think of one blazar class as a gas-guzzling car and the other as an energy-efficient electric vehicle,” said lead researcher Marco Ajello, an astrophysicist at Clemson University in South Carolina. “Our results suggest that we’re actually seeing hybrids, which tap into the energy of their black holes in different ways as they age.”

    Active galaxies possess extraordinarily luminous cores powered by black holes containing millions or even billions of times the mass of the sun. As gas falls toward these supermassive black holes, it settles into an accretion disk and heats up. Near the brink of the black hole, through processes not yet well understood, some of the gas blasts out of the disk in jets moving in opposite directions at nearly the speed of light.

    smbh
    An artist’s conception of a supermassive black hole and accretion disk.

    Blazars are the highest-energy type of active galaxy and emit light across the spectrum, from radio to gamma rays. They make up more than half of the discrete gamma-ray sources cataloged by Fermi’s Large Area Telescope, which has detected more than 1,000 to date. Astronomers think blazars appear so intense because they happen to tip our way, bringing one jet nearly into our line of sight. Looking almost directly down the barrel of a particle jet moving near the speed of light, emissions from the jet and the region producing it dominate our view.

    To be considered a blazar, an active galaxy must show either rapid changes in visible light on timescales as short as a few days, strong optical polarization, or glow brightly at radio wavelengths with a “flat spectrum” — that is, one exhibiting relatively little change in brightness among neighboring frequencies.

    Astronomers have identified two models in the blazar line. One, known as flat-spectrum radio quasars (FSRQs), show strong emission from an active accretion disk, much higher luminosities, smaller black hole masses and lower particle acceleration in the jets. The other, called BL Lacs, are totally dominated by the jet emission, with the jet particles reaching much higher energy and the accretion disk emission either weak or absent.

    disc
    Ring Around a Suspected Black Hole in Galaxy NGC 4261.
    Image taken by Hubble space telescope of what may be gas accreting onto a black hole in elliptical galaxy NGC 4261

    Speaking at the American Astronomical Society meeting in Boston on Tuesday, Ajello said he and his team wanted to probe how the distribution of these objects changed over the course of cosmic history, but solid distance information for large numbers of gamma-ray-producing BL Lac objects was hard to come by.

    “One of our most important tools for determining distance is the movement of spectral lines toward redder wavelengths as we look deeper into the cosmos,” explained team member Dario Gasparrini, an astronomer at the Italian Space Agency’s Science Data Center in Rome. “The weak disk emission from BL Lacs makes it extremely difficult to measure their redshift and therefore to establish a distance.”

    So the team undertook an extensive program of optical observations to measure the redshifts of BL Lac objects detected by Fermi.

    “This project has taken several years and simply wouldn’t have been possible without the extensive use of many ground-based observatories by our colleagues,” said team member Roger Romani, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology, a facility run jointly by Stanford University and the SLAC National Accelerator Laboratory in Menlo Park, California.

    The redshift survey included 25 nights on the Hobby-Eberly Telescope at McDonald Observatory in Texas, led by Romani; eight nights on the 200-inch telescope at Palomar Observatory and nine nights on the 10-meter Keck Telescope in Hawaii, led by Anthony Readhead at Caltech in Pasadena, California; and nine nights on telescopes at the European Southern Observatory in Chile, led by Garret Cotter at the University of Oxford in England. In addition, important observations were provided by the Chile-based GROND camera, led by Jochen Greiner at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and the Ultraviolet/Optical Telescope on NASA’s Swift satellite, led by Neil Gehrels at Goddard Space Flight Center in Greenbelt, Maryland.

    Hobby-Eberly Telescope
    Hobby-Eberly Telescope

    Caltech Palomar Observatory
    Palomar

    Keck Observatory
    Keck

    With distances for about 200 BL Lacs in hand — the largest and most comprehensive sample available to date — the astronomers could compare their distribution across cosmic time with a similar sample of FSRQs. What emerged suggests that, starting around 5.6 billion years ago, FSRQs began to decline while BL Lacs underwent a steady increase in numbers. The rise is particularly noticeable among BL Lacs with the most extreme energies, which are known as high-synchrotron-peaked blazars based on a particular type of emission.

    “What we think we’re seeing here is a changeover from one style of extracting energy from the central black hole to another,” adds Romani.

    Large galaxies grew out of collisions and mergers with many smaller galaxies, and this process occurs with greater frequency as we look back in time. These collisions provided plentiful gas to the growing galaxy and kept the gas stirred up so it could more easily reach the central black hole, where it piled up into a vast, hot, and bright accretion disk like those seen in “gas-guzzling” FSRQs. Some of the gas near the hole powers a jet while the rest falls in and gradually increases the black hole’s spin.

    As the universe expands and the density of galaxies decreases, so do galaxy collisions and the fresh supply of gas they provide to the black hole. The accretion disk becomes depleted over time, but what’s left is orbiting a faster-spinning and more massive black hole. These properties allow BL Lac objects to maintain a powerful jet even though relatively meager amounts of material are spiraling toward the black hole.

    In effect, the energy of accretion from the galaxy’s days as an FSRQ becomes stored in the increasing rotation and mass of its black hole, which acts much like a battery. When the gas-rich accretion disk all but disappears, the blazar taps into the black hole’s stored energy that, despite a lower accretion rate, allows it to continue operating its particle jet and producing high-energy emissions as a BL Lac object.

    One observational consequence of the hybrid blazar notion is that the luminosity of BL Lacs should decrease over time as the black hole loses energy and spins down.

    The astronomers say they are eager to test this idea with larger blazar samples provided in part by Fermi’s continuing all-sky survey. Understanding the details of this transition also will require better knowledge of the jet, the black hole mass and the galaxy environment for both blazar classes.

    See the full article here.


    ScienceSprings is powered by MAINGEAR computers

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
Follow

Get every new post delivered to your Inbox.

Join 462 other followers

%d bloggers like this: