NASA'S Swift Satellite Spots Black Hole Devouring A Star

[NASA News <hqnews@xxxxxxxxxxxxxxxxxxxxxx>]

Aug. 24, 2011

Trent J. Perrotto 
Headquarters, Washington 
202-358-0321 
trent.j.perrotto@xxxxxxxx 

Lynn Chandler 
Goddard Space Flight Center, Greenbelt, Md. 
301-286-2806 
lynn.chandler-1@xxxxxxxx        


RELEASE: 11-271

NASA'S SWIFT SATELLITE SPOTS BLACK HOLE DEVOURING A STAR

WASHINGTON -- 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. 

"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." 

Swift, launched in November 2004, is managed by NASA's Goddard Space 
Flight Center in Greenbelt, Md. It is operated in collaboration with 
Penn State, the Los Alamos National Laboratory in N.M. and Orbital 
Sciences Corp., in Dulles, Va., with international collaborators in 
the U.K., Italy, Germany and Japan. MAXI is operated by the Japan 
Aerospace Exploration Agency as an external experiment attached to 
the Kibo module of the space station. For images and animations 
related to the studies, visit: 






http://www.nasa.gov/swift   

	
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