Max Planck Institute for Radio Astronomy | 2011 Aug 24
Observations from Radio to Gamma rays detail how a Black Hole devoured a Star
The source now known as Swift J1644+57 is the result of a truly extraordinary event -- the awakening of a distant galaxy's dormant black hole as it shredded and consumed an errant star. Two new studies, one of them highlighting X- and gamma-ray observations from NASA's Swift and other detectors, the other examining the unprecedented outburst through observations from numerous ground-based radio observatories describe the event throughout the electromagnetic spectrum. Andreas Brunthaler from Max-Planck-Institut für Radioastronomie in Bonn is co-author of the radio study which includes observations with the Expanded Very Large Array (EVLA). The results will be published in this week's issue of "Nature".
Most galaxies, including our own, possess a central supersized black hole weighing millions of times the sun's mass. The black hole in the galaxy hosting Swift J1644+57 may be twice the mass of the four-million-solar-mass black hole lurking at the center of our own Milky Way galaxy. As a star falls toward a black hole, it is ripped apart by intense tides. The gas is corralled into an accretion disk that swirls around the black hole and becomes rapidly heated to temperatures of millions of degrees.
The innermost gas in the disk spirals toward the black hole, where rapid orbital motion magnifies its magnetic field and creates dual, oppositely directed "funnels" through which some particles may escape. Particle jets driving matter at velocities greater than 90 percent the speed of light form along the black hole's spin axis. In the case of Swift J1644+57, one of these jets happened to point straight at Earth.
"The radio emission occurs when the outgoing jet slams into the interstellar environment", explains Ashley Zauderer, leading author of the radio study. "By contrast, the X-rays arise much closer to the black hole, likely near the base of the jet."
Theoretical studies of tidally disrupted stars suggested that they would appear as flares at optical and ultraviolet energies. Thanks to the rules of relativity, the brightness and energy of a black hole's jet is greatly enhanced when viewed head-on. The phenomenon, called relativistic beaming, explains why Swift J1644+57 was seen at X-ray energies and appeared so strikingly luminous.
When first detected with NASA's Swift satellite on March 28, the flares were initially assumed to signal a gamma-ray burst, one of the nearly daily short blasts of high-energy radiation often associated with the death of a massive star and the birth of a black hole in the distant universe. But as the emission continued to brighten and flare, astronomers realized that the most plausible explanation was the tidal disruption of a sun-like star seen as beamed emission.
Two days later, on March 30, EVLA observations by Zauderer's team showed a brightening radio source centered on a faint galaxy near Swift's position for the X-ray flares. These data provided the first conclusive evidence that the galaxy, the radio source and the Swift event were linked.
The observations show that the radio-emitting region is still expanding at more than half the speed of light. Tracking this expansion backward in time could confirm that the outflow formed at the same time as the Swift X-ray source."
According to relativity, looking "down the barrel" of a particle jet also distorts time, making the jet's evolution appear to unfold many times slower than it actually is. "We expect that within two years the jet should be about 12 light-years across", says Andreas Brunthaler from the Max-Planck-Institut für Radioastronomie in Bonn, co-author of the radio paper. "Despite the galaxy's enormous distance of 3.8 billion light-years, this is large enough that the jet will be resolvable using VLBI technique." Very Large Baseline Interferometry (VLBI) combines data from widely separated radio telescopes to emulate one nearly Earth's size. For the observations of Swift 1644+57 the VLBA network in the U.S. and the 100 m Effelsberg radio telescope in Germany are jointly used as a vrtual radio telescope across the Atlantic ocean.
"Incredibly, this source is still producing X-rays and may remain bright enough for Swift to observe into next year," said David Burrows, a professor of astronomy at Penn State University, lead scientist for the mission's X-Ray Telescope (XRT) instrument team. "It behaves unlike anything we've seen before."
Two studies appearing in the Aug. 25 issue of the journal Nature provide new insights into a cosmic accident that has been streaming X-rays toward Earth since late March. That's when NASA's Swift satellite first alerted astronomers to intense and unusual high-energy flares from a new source in the constellation Draco.
Birth of a relativistic outflow in the unusual γ-ray transient Swift J164449.3+573451 - B. A. Zauderer et al
- Nature 476 425 (25 Aug 2011) DOI: 10.1038/nature10366
arXiv.org > astro-ph > arXiv:1106.3568 > 17 Jun 2011
- Nature 476 421 (25 Aug 2011) DOI: 10.1038/nature10374
- arXiv.org > astro-ph > arXiv:1104.4787 > 25 Apr 2011 (v1), 27 Apr 2011 (v2)
Researchers Detail How A Distant Black Hole Devoured A Star
NASA GSFC | Swift | 2011 Aug 24
Two studies appearing in the Aug. 25 issue of the journal Nature provide new insights into a cosmic accident that has been streaming X-rays toward Earth since late March. NASA's Swift satellite first alerted astronomers to intense and unusual high-energy flares from the new source in the constellation Draco.Click to play embedded YouTube video.Video Credit: NASA/GSFC/CI Lab[hr][/hr]
"Incredibly, this source is still producing X-rays and may remain bright enough for Swift to observe into next year," said David Burrows, professor of astronomy at Penn State University and lead scientist for the mission's X-Ray Telescope instrument. "It behaves unlike anything we've seen before."
Astronomers soon realized the source, known as Swift J1644+57, was the result of a truly extraordinary event -- the awakening of a distant galaxy's dormant black hole as it shredded and consumed a star. The galaxy is so far away, it took the light from the event approximately 3.9 billion years to reach Earth.
Burrows' study included NASA scientists. It highlights the X- and gamma-ray observations from Swift and other detectors, including the Japan-led Monitor of All-sky X-ray Image (MAXI) instrument aboard the International Space Station.
The second study was led by Ashley Zauderer, a post-doctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. It examines the unprecedented outburst through observations from numerous ground-based radio observatories, including the National Radio Astronomy Observatory's Expanded Very Large Array (EVLA) near Socorro, N.M.
Most galaxies, including our own, possess a central supersized black hole weighing millions of times the sun's mass. According to the new studies, the black hole in the galaxy hosting Swift J1644+57 may be twice the mass of the four-million-solar-mass black hole in the center of the Milky Way galaxy. As a star falls toward a black hole, it is ripped apart by intense tides. The gas is corralled into a disk that swirls around the black hole and becomes rapidly heated to temperatures of millions of degrees.
The innermost gas in the disk spirals toward the black hole, where rapid motion and magnetism create dual, oppositely directed "funnels" through which some particles may escape. Jets driving matter at velocities greater than 90 percent the speed of light form along the black hole's spin axis. In the case of Swift J1644+57, one of these jets happened to point straight at Earth.
"The radio emission occurs when the outgoing jet slams into the interstellar environment," Zauderer explained. "By contrast, the X-rays arise much closer to the black hole, likely near the base of the jet."
Theoretical studies of tidally disrupted stars suggested they would appear as flares at optical and ultraviolet energies. The brightness and energy of a black hole's jet is greatly enhanced when viewed head-on. The phenomenon, called relativistic beaming, explains why Swift J1644+57 was seen at X-ray energies and appeared so strikingly luminous.
When first detected March 28, the flares were initially assumed to signal a gamma-ray burst, one of the nearly daily short blasts of high-energy radiation often associated with the death of a massive star and the birth of a black hole in the distant universe. But as the emission continued to brighten and flare, astronomers realized that the most plausible explanation was the tidal disruption of a sun-like star seen as beamed emission.
By March 30, EVLA observations by Zauderer's team showed a brightening radio source centered on a faint galaxy near Swift's position for the X-ray flares. These data provided the first conclusive evidence that the galaxy, the radio source and the Swift event were linked.
"Our observations show that the radio-emitting region is still expanding at more than half the speed of light," said Edo Berger, an associate professor of astrophysics at Harvard and a coauthor of the radio paper. "By tracking this expansion backward in time, we can confirm that the outflow formed at the same time as the Swift X-ray source."
First observation of a massive black hole swallowing a star
Japan Aerospace Exploration Agency | 2011 Aug 25
The Monitor of All-sky X-ray Image (MAXI) on Kibo, in coordination with the gamma-ray burst satellite Swift (USA), observed the instant that a massive black hole swallowed a star for the first time in the world, located in the center of a galaxy 3.9 billion light years away. This result was published in Nature online, issued on August 25 Japan time. The title of the paper is "Relativistic Jet Activity from the Tidal Disruption of a Star by a Massive Black Hole".
The Swift team, led by Prof. David Burrows of Penn State University, who is also the main author of this paper, detected a strong gamma ray coming from the object located in Draco constellation with a BAT instrument at 21:57 on March 28, 2011 (JST). This object, named Swift J1644+57, continued strong X-ray emissions, so we understood it as different from a gamma-ray burst, as is often observed when a massive star dies and a black hole is born.
Alerted by information from the Swift team, the MAXI team, including JAXA, Riken, and Profs. Nobuyuki Kawai in Tokyo Tech and Hitoshi Negoro in Nihon University, both of whom co-authored the Nature paper, reviewed the MAXI data of this object and found that MAXI had detected X-rays from Swift J1644+57 several hours before the Swift discovery. They also found that there had been no previous X-ray emission before the activity this time.
Detailed analysis of MAXI and Swift observations revealed that the X-ray came from a black hole located in the center of a galaxy sucking down a star. This was the first time that a nucleus with no X-ray emission had ever suddenly started such activity. The strong X-ray and rapid variation indicated that the X-ray came from a jet. Although there have been some other observations to date, namely considered to be tidal disruption and a black hole swallowing a star, they were not as violent as seen this time, and the beginning had not previously been observed.
MAXI was mounted on the Japanese experimental module Kibo on the ISS in July 2009 and has been monitoring the whole sky since August 2009. Moreover, MAXI can not only detect transient objects, but is also capable of investigating the state of objects prior to the phenomenon, which led to the current discovery. The X-ray camera with MAXI can detect low-energy X-rays, enabling wide-ranging coverage when combined with Swift BAT. Continual monitoring of MAXI will lead to further new discoveries in future.
Swift satellite alerts astronomers to cosmic accident in constellation Draco
Smithsonian Science | 2011 Aug 24
Black hole caught grabbing a starry treat
New Scientist | Maggie McKee | 2011 Aug 24
Black Hole Caught in Act of Swallowing Star
Space.com | Charles Q Choi | 2011 Aug 25
More Details on the Black Hole that Swallowed a Screaming Star
Universe Today | Nancy Atkinson | 2011 Aug 25
Star eaten by a black hole: still blasting away
Discover Blogs | Bad Astronomy | 2011 Aug 26
Black Hole Behemoth Found Guilty of Star's Murder
Discovery News | Ian O'Niell | 2011 Aug 26
