In its first year, NASA's Fermi Gamma-ray Space Telescope discovered GeV (billions of electron volts) intensity variations revealing orbital motion in high-mass X-ray binaries (HMXBs). These are systems where a compact companion, such as a neutron star or a black hole, rapidly orbits a hot, young, massive star. The first examples include LSI +61 303, which sports a 26-day orbital period, and LS 5039 (3.9 days). This animation shows such a system. When the compact object lies far from its host star, TeV (trillions of electron volts) gamma-rays (white) are seen by ground-based gamma-ray observatories. But, as the object plunges closer to the star, the TeV emission is quenched and GeV emission turns on. Interactions by accelerated particles from the compact source with gas encircling the star — or in some systems, the star's light itself — is thought to be responsible for this change. ||

This animation was used to illustrate a gamma ray burst that NASA's SWIFT might see. || Gamma Ray Burst || GRBHD039100377_print.jpg (1024x576) [43.9 KB] || GRBHD0391_web.png (320x180) [267.8 KB] || GRBHD0391_thm.png (80x40) [15.0 KB] || 1280x720_16x9_60p (1280x720) [32.0 KB] || grb_hd_720p.m2v (1280x720) [20.5 MB] || grb_hd_720p.webmhd.webm (960x540) [2.0 MB] || a010245_grb_hd_720p.mp4 (640x360) [1.6 MB] || grb_hd_512x288.m1v (512x288) [2.9 MB] ||

Scientists using NASA's Swift satellite say they have found newborn black holes, just seconds old, in a confused state of existence, sloppily gorging on material falling into them while somehow propelling other material away at great speeds. These black holes are born in massive star explosions. An initial blast obliterates the star. Yet the chaotic black hole activity appears to re-energize the explosion again and again over the course of several minutes. This is a dramatically different view of star death, one that entails multiple explosive outbursts and not just a single bang, as previously thought.When a massive star runs out of fuel, it no longer has the energy to support its mass. The core collapses and forms a black hole. Shockwaves bounce out and obliterate the outer shells of the star. Previously scientists thought that a single explosion is followed by a graceful afterglow of the dying embers. Now, according to Swift observations, it appears that a newborn black hole in the core somehow re-energizes the explosion again and again, creating multiple bursts all within a few minutes. ||

Gamma-ray bursts that are longer than two seconds are caused by the detonation of a rapidly rotating massive star at the end of its life on the main sequence. Jets of particles and gamma radiation are emitted in opposite directions from the stellar core as the star collapses. In this model, a narrow beam of gamma rays is emitted, followed by a wider beam of gamma rays. The narrow beam for GRB 080319B was aimed almost precisely at the Earth, which made it the brightest gamma-ray burst observed to date by NASA's Swift satellite. ||

Animation of the Swift spacecraft. ||

In late June 2013, an exceptional binary system 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.The 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. To better understand J1023's spin and orbital evolution, the system was routinely monitored in radio. 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.What's happening, astronomers say, are the last sputtering throes of the pulsar spin-up process. Researchers regard the system as a unique laboratory for understanding how millisecond pulsars form and for studying details of how accretion takes place on neutron stars. 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. When gas from the disk 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. Some of the gas may be accelerated outward at nearly the speed of light, forming dual particle jets firing in opposite directions. Shock waves within and along the periphery of these jets are a likely source of the bright gamma-ray emission detected by Fermi. ||

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 ||

Swift searches for Gamma Ray Bursts and stellar explosions ||

On Thursday, Nov. 21, 2013, NASA held a media teleconference to discuss new findings related to a brilliant gamma-ray burst detected on April 27. Audio of the teleconference is available for download here.Related feature story: www.nasa.gov/content/goddard/nasa-sees-watershed-cosmic-blast-in-unique-detail/.Audio of Sylvia Zhu interview for a Science Podcast. Briefing Speakers Introduction: Paul Hertz, NASA Astrophysics Division Director, NASA Headquarters, Washington, D.C.Charles Dermer, astrophysicist, Naval Research Laboratory, Washington, D.C.Thomas Vestrand, astrophysicist, Los Alamos National Laboratory, Los Alamos, N.M.Chryssa Kouveliotou, astrophysicist, NASA’s Marshall Space Flight Center, Huntsville, Ala. Presenter 1: Charles Dermer ||

Most large galaxies contain a giant central black hole. In an active galaxy, matter falling toward the supermassive black hole powers high-energy emissions so intense that two classes of active galaxies, quasars and blazars, rank as the most luminous objects in the universe. Thick clouds of dust and gas near the central black hole screens out ultraviolet, optical and low-energy (or soft) X-ray light. Although there are many different types of active galaxy, astronomers explain the different observed properties based on how the galaxy angles into our line of sight. We view the brightest ones nearly face on, but as the angle increases, the surrounding ring of gas and dust absorbs increasing amounts of the black hole's emissions. ||