Swift: Neutron Stars

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  • NASA Missions Unveil Magnetar Eruptions in Nearby Galaxies
    On April 15, 2020, a brief burst of high-energy light swept through the solar system, triggering instruments on many NASA missions. Now, multiple international science teams conclude that the blast came from a supermagnetized stellar remnant known as a magnetar located in a neighboring galaxy. This finding confirms long-held suspicions that some gamma-ray bursts (GRBs) – cosmic eruptions detected somewhere in the sky almost daily – are in fact powerful flares from magnetars relatively close to home. The April 15 event is a game changer because its estimated location lies entirely within the disk of the galaxy NGC 253, located 11.4 million light-years away GRBs, the most powerful explosions in the cosmos, can be detected across billions of light-years. Those lasting less than about two seconds, called short GRBs, occur when a pair of orbiting neutron stars both the crushed remnants of exploded stars spiral into each other and merge. Magnetars are neutron stars with the strongest-known magnetic fields, with up to a thousand times the intensity of typical neutron stars and up to 10 trillion times the strength of a refrigerator magnet. Rarely, magnetars produce enormous eruptions called giant flares that produce gamma rays, the highest-energy form of light. Shortly before 4:42 a.m. EDT on April 15, a powerful burst of X-rays and gamma rays triggered, in turn, instruments on NASA's Mars Odyssey mission, Wind satellite, and Fermi Gamma-ray Space Telescope. A ground-based analysis of data from NASA's Neil Gehrels Swift Observatory show that it also detected the event. The pulse of radiation lasted just 140 milliseconds, as fast as a blink of the eye or a finger snap. Fermi's Large Area Telescope (LAT) also detected high-energy gamma rays up to several minutes after this pulse, a surprising finding. Analysis of Fermi and Swift data indicate that the outburst launched a blob of electrons and positrons moving at about 99% the speed of light. The blob expanded as it traveled, following closely behind the light emitted by the giant flare. After a few days, scientists say, they reached the boundary separating the magnetar's region of influence from interstellar space. The light passed through, followed many seconds later by the greatly expanded cloud. This material induced shock waves in gas piled up at the boundary, and the interaction produced the highest-energy emission detected by the LAT.
  • NASA Missions Team Up to Study Unique Magnetar Outburst
    On April 28, a supermagnetized stellar remnant known as a magnetar blasted out a simultaneous mix of X-ray and radio signals never observed before. The flare-up included the first fast radio burst (FRB) ever seen from within our Milky Way galaxy and shows that magnetars can produce these mysterious and powerful radio blasts previously only seen in other galaxies. A magnetar is a type of isolated neutron star, the crushed, city-size remains of a star many times more massive than our Sun. What makes a magnetar so special is its intense magnetic field. The field can be 10 trillion times stronger than a refrigerator magnet's and up to a thousand times stronger than a typical neutron star's. This represents an enormous storehouse of energy that astronomers suspect powers magnetar outbursts. The X-ray portion of the synchronous bursts was detected by several satellites, including NASA's Wind mission. The radio component was discovered by the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope located at Dominion Radio Astrophysical Observatory in British Columbia and led by several Canadian universities. It was also detected by the NASA-funded Survey for Transient Astronomical Radio Emission 2 (STARE2), a trio of detectors in California and Utah operated by Caltech and NASA’s Jet Propulsion Laboratory in Southern California. The STARE2 data showed that the burst's energy was comparable to FRBs. By the time these bursts occurred, astronomers had already been monitoring their source, a magnetar named SGR 1935+2154, for more than half a day using NASA's Neil Gehrels Swift Observatory, Fermi Gamma-ray Space Telescope, and the Neutron star Interior Composition Explorer (NICER) X-ray telescope mounted atop the International Space Station. About 13 hours later, when the magnetar was out of view for Swift, Fermi and NICER, a special X-ray burst erupted. The blast was seen by the European Space Agency’s INTEGRAL mission, the China National Space Administration’s Huiyan X-ray satellite, and the Russian Konus instrument on Wind. As the half-second-long X-ray burst flared, CHIME and STARE2 detected the radio burst, which lasted only a thousandth of a second. Taken together, the observations strongly suggest that the magnetar produced the Milky Way galaxy's equivalent of an FRB, which means magnetars in other galaxies likely produce at least some of these signals.
  • Doomed Neutron Stars Create Blast of Light and Gravitational Waves
    For the first time, NASA scientists have detected light tied to a gravitational-wave event, thanks to two merging neutron stars in the galaxy NGC 4993, located about 130 million light-years from Earth in the constellation Hydra. Shortly after 8:41 a.m. EDT on Aug. 17, NASA's Fermi Gamma-ray Space Telescope picked up a pulse of high-energy light from a powerful explosion, which was immediately reported to astronomers around the globe as a short gamma-ray burst. The scientists at the National Science Foundation’s Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves dubbed GW170817 from a pair of smashing stars tied to the gamma-ray burst, encouraging astronomers to look for the aftermath of the explosion. Shortly thereafter, the burst was detected as part of a follow-up analysis by ESA’s (European Space Agency’s) INTEGRAL satellite. NASA's Swift, Hubble, Chandra and Spitzer missions, along with dozens of ground-based observatories, including the NASA-funded Pan-STARRS survey, later captured the fading glow of the blast's expanding debris. Neutron stars are the crushed, leftover cores of massive stars that previously exploded as supernovas long ago. The merging stars likely had masses between 10 and 60 percent greater than that of our Sun, but they were no wider than Washington, D.C. The pair whirled around each other hundreds of times a second, producing gravitational waves at the same frequency. As they drew closer and orbited faster, the stars eventually broke apart and merged, producing both a gamma-ray burst and a rarely seen flare-up called a "kilonova." Neutron star mergers produce a wide variety of light because the objects form a maelstrom of hot debris when they collide. Merging black holes -- the types of events LIGO and its European counterpart, Virgo, have previously seen -- very likely consume any matter around them long before they crash, so we don't expect the same kind of light show. Within hours of the initial Fermi detection, LIGO and the Virgo detector at the European Gravitational Observatory near Pisa, Italy, greatly refined the event's position in the sky with additional analysis of gravitational wave data. Ground-based observatories then quickly located a new optical and infrared source -- the kilonova -- in NGC 4993. To Fermi, this appeared to be a typical short gamma-ray burst, but it occurred less than one-tenth as far away as any other short burst with a known distance, making it among the faintest known. Astronomers are still trying to figure out why this burst is so odd, and how this event relates to the more luminous gamma-ray bursts seen at much greater distances. NASA’s Swift, Hubble and Spitzer missions followed the evolution of the kilonova to better understand the composition of this slower-moving material, while Chandra searched for X-rays associated with the remains of the ultra-fast jet.
  • NASA's Swift Catches an Anti-glitch from a Neutron Star
    Using observations by NASA's Swift satellite, an international team of astronomers has identified an abrupt slowdown in the rotation of a neutron star. The discovery holds important clues for understanding some of the densest matter in the universe.

    While astronomers have witnessed hundreds of events, called glitches, associated with sudden increases in the spin of neutron stars, the sudden spin-down caught them off guard.

    A neutron star is the crushed core of a massive star that ran out of fuel, collapsed under its own weight, and exploded as a supernova. It's the closest thing to a black hole that astronomers can observe directly, compressing half a million times Earth's mass into a ball roughly the size of Manhattan Island. Matter within a neutron star is so dense that a teaspoonful would weigh about a billion tons on Earth.

    Neutron stars possess two other important traits. They spin rapidly, ranging from a few rpm to as many as 43,000, comparable to the blades of a kitchen blender, and they boast magnetic fields a trillion times stronger than Earth's.

    About two dozen neutron stars occasionally produce high-energy explosions that astronomers say require magnetic fields thousands of times stronger than expected. These exceptional objects, called magnetars, are routinely monitored by a McGill team led by Kaspi using Swift's X-Ray Telescope.

    Read the rest of the story here.

  • Fermi Finds Hints of Starquakes in Magnetar 'Storm'
    Astronomers analyzing data acquired by NASA's Fermi Gamma-ray Space Telescope during a rapid-fire "storm" of high-energy blasts in 2009 have discovered underlying signals related to seismic waves rippling throughout the host neutron star. The burst storm came from SGR J1550−5418, a neutron star with a super-strong magnetic field, also known as a magnetar. Located about 15,000 light-years away in the constellation Norma, the magnetar was quiet until October 2008, when it entered a period of eruptive activity that ended in April 2009. At times, the object produced hundreds of bursts in as little as 20 minutes, and the most intense explosions emitted more total energy than the sun does in 20 years. High-energy instruments on many spacecraft, including NASA's Swift and Rossi X-ray Timing Explorer, detected hundreds of gamma-ray and X-ray blasts. An examination of 263 individual bursts detected by Fermi's Gamma-ray Burst Monitor confirms vibrations in the frequency ranges previously only seen in rare giant flares from magnetars. Astronomers suspect these are twisting oscillations of the star where the crust and the core, bound by the magnetic field, vibrate together. In addition, a single burst showed an oscillation at a frequency never seen before and which scientists still do not understand. While there are many efforts to describe the interiors of neutron stars, scientists lack enough observational detail to choose between differing models. Neutron stars reach densities far beyond the reach of laboratories and their interiors may exceed the density of an atomic nucleus by as much as 10 times. Knowing more about how bursts shake up these stars will give theorists an important new window into understanding their internal structure. Magnetar Burst with Torsional WavesMagnetar Burst Unlabled still of Fermi here
  • Neutron Star Merge
    Binary systems containing neutron stars are born when the cores of two orbiting stars collapse in supernova explosions. Neutron stars pack the mass of our sun into the size of a city. They are so dense and packed so tightly that the boundaries atoms nuclei disappear. In such systems, Einstein's theory of general relativity predicts that neutron stars emit gravitational radiation, ripples of space-time. This causes the orbits to shrink and gradually brings the neutron stars closer together. Shown here is such a system after about 1 billion years, when two equal-mass neutron whirl around each other at 60,000 times a minute. The stars merge in a few milliseconds, sending out a burst of gravitational waves and a brief, intense gamma-ray burst.
  • When Neutron Stars Collide
    Armed with state-of-the-art supercomputer models, scientists have shown that colliding neutron stars can produce the energetic jet required for a gamma-ray burst. Earlier simulations demonstrated that mergers could make black holes. Others had shown that the high-speed particle jets needed to make a gamma-ray burst would continue if placed in the swirling wreckage of a recent merger.

    Now, the simulations reveal the middle step of the process—how the merging stars' magnetic field organizes itself into outwardly directed components capable of forming a jet. The Damiana supercomputer at Germany's Max Planck Institute for Gravitational Physics needed six weeks to reveal the details of a process that unfolds in just 35 thousandths of a second—less than the blink of an eye.

    For the researchers' website, with more video and stills of their simulations, go here.

  • Neutron Stars Rip Each Other Apart to Form Black Hole
    This supercomputer simulation shows one of the most violent events in the universe: a pair of neutron stars colliding, merging and forming a black hole. A neutron star is the compressed core left behind when a star born with between eight and 30 times the sun's mass explodes as a supernova. Neutron stars pack about 1.5 times the mass of the sun — equivalent to about half a million Earths — into a ball just 12 miles (20 km) across. As the simulation begins, we view an unequally matched pair of neutron stars weighing 1.4 and 1.7 solar masses. They are separated by only about 11 miles, slightly less distance than their own diameters. Redder colors show regions of progressively lower density. As the stars spiral toward each other, intense tides begin to deform them, possibly cracking their crusts. Neutron stars possess incredible density, but their surfaces are comparatively thin, with densities about a million times greater than gold. Their interiors crush matter to a much greater degree densities rise by 100 million times in their centers. To begin to imagine such mind-boggling densities, consider that a cubic centimeter of neutron star matter outweighs Mount Everest. By 7 milliseconds, tidal forces overwhelm and shatter the lesser star. Its superdense contents erupt into the system and curl a spiral arm of incredibly hot material. At 13 milliseconds, the more massive star has accumulated too much mass to support it against gravity and collapses, and a new black hole is born. The black hole's event horizon — its point of no return — is shown by the gray sphere. While most of the matter from both neutron stars will fall into the black hole, some of the less dense, faster moving matter manages to orbit around it, quickly forming a large and rapidly rotating torus. This torus extends for about 124 miles (200 km) and contains the equivalent of 1/5th the mass of our sun. The entire simulation covers only 20 milliseconds. Scientists think neutron star mergers like this produce short gamma-ray bursts (GRBs). Short GRBs last less than two seconds yet unleash as much energy as all the stars in our galaxy produce over one year. The rapidly fading afterglow of these explosions presents a challenge to astronomers. A key element in understanding GRBs is getting instruments on large ground-based telescopes to capture afterglows as soon as possible after the burst. The rapid notification and accurate positions provided by NASA's Swift mission creates a vibrant synergy with ground-based observatories that has led to dramatically improved understanding of GRBs, especially for short bursts.
  • A Flickering X-ray Candle
    The Crab Nebula, created by a supernova seen nearly a thousand years ago, is one of the sky's most famous "star wrecks." For decades, most astronomers have regarded it as the steadiest beacon at X-ray energies, but data from orbiting observatories show unexpected variations, showing astronomers their hard X-ray "standard candle" isn't as steady as they once thought. From 1999 to 2008, the Crab brightened and faded by as much as 3.5 percent a year, and since 2008, it has faded by 7 percent. The Gamma-ray Burst Monitor on NASA's Fermi satellite first detected the decline, and Fermi's Large Area Telescope also spotted two gamma-ray flares at even higher energies. Scientists think the X-rays reveal processes deep within the nebula, in a region powered by a rapidly spinning neutron star — the core of the star that blew up. But figuring out exactly where the Crab's X-rays are changing over the long term will require a new generation of X-ray telescopes.
  • Cosmic Explosion Second Only to the Sun in Brightness
    The gamma ray flare produced by neutron star SGR 1806-20, traveled 50,000 light years before impacting Earth. The burst was so powerful, that it disrupted Earth's ionosphere. Scientists know of only two other giant flares in the past 35 years, and this December 27, 2005 event was one hundred times more powerful than either of those
  • Soft Gamma-Ray Repeater Light Echoes Captured by Swift Satellite
    The X-Ray Telescope (XRT) aboard NASA's Swift satellite captured light echoes from a soft-gamma-ray repeater. These stellar remnants, which are thought to be highly magnetized neutron stars called magnetars, occasionally belt out a series of X- and gamma-ray flares. On Jan. 22, 2009, an object known as SGR J1550-5418 began its second and most intense round of outbursts since October 2008. In the following days, Swift's XRT captured what appears to be an expanding halo as X-rays from the brightest bursts scatter off of intervening dust. Multiple rings form as the X-rays interact with different dust clouds. Closer clouds produce larger rings. Both the rings and their apparent expansion are an effect of light's finite speed and the longer path the scattered light must travel. They will be studied to make a more reliable measurement of the distance to the source and to the dust clouds.
  • Vela Pulsar in Gamma Rays
    This movie shows pulsed gamma rays from the Vela pulsar as constructed from photons detected by Fermi's Large Area Telescope. The Vela pulsar, which spins 11 times a second, is the brightest persistent source of gamma rays in the sky. The movie includes data from August 4 to Sept. 15, 2008. The bluer color in the latter part of the pulse indicates the presence of gamma rays with energies exceeding a billion electron volts (1 GeV). For comparison, visible light has energies between two and three electron volts. Red indicates gamma rays with energies less than 300 million electron volts (MeV); green, gamma rays between 300 MeV and 1 GeV; and blue shows gamma rays greater than 1 GeV. The movie frame is 30 degrees across. The background, which shows diffuse gamma-ray emission from the Milky Way, is about 15 times brighter here than it actually is.