NASA's Swift Satellite Discovers A New Black Hole In Our Galaxy

[Date Prev] [Date Next] [Thread Prev] [Thread Next] [Date Index] [Thread Index]

 



Oct. 5, 2012

J.D. Harrington 
Headquarters, Washington 
202-358-5241 
j.d.harrington@xxxxxxxx 

Rob Gutro 
Goddard Space Flight Center, Greenbelt, Md. 
301-286-4044 
robert.j.gutro@xxxxxxxx 

RELEASE: 12-353

NASA'S SWIFT SATELLITE DISCOVERS A NEW BLACK HOLE IN OUR GALAXY

WASHINGTON -- NASA's Swift satellite recently detected a rising tide 
of high-energy X-rays from a source toward the center of our Milky 
Way galaxy. The outburst, produced by a rare X-ray nova, announced 
the presence of a previously unknown stellar-mass black hole. 

"Bright X-ray novae are so rare that they're essentially 
once-a-mission events and this is the first one Swift has seen," said 
Neil Gehrels, the mission's principal investigator, at NASA's Goddard 
Space Flight Center in Greenbelt, Md. "This is really something we've 
been waiting for." 

An X-ray nova is a short-lived X-ray source that appears suddenly, 
reaches its emission peak in a few days and then fades out over a 
period of months. The outburst arises when a torrent of stored gas 
suddenly rushes toward one of the most compact objects known, either 
a neutron star or a black hole. 

The rapidly brightening source triggered Swift's Burst Alert Telescope 
twice on the morning of Sept. 16, and once again the next day. 

Named Swift J1745-26 after the coordinates of its sky position, the 
nova is located a few degrees from the center of our galaxy toward 
the constellation Sagittarius. While astronomers do not know its 
precise distance, they think the object resides about 20,000 to 
30,000 light-years away in the galaxy's inner region. 

Ground-based observatories detected infrared and radio emissions, but 
thick clouds of obscuring dust have prevented astronomers from 
catching Swift J1745-26 in visible light. 

The nova peaked in hard X-rays -- energies above 10,000 electron 
volts, or several thousand times that of visible light -- on Sept. 
18, when it reached an intensity equivalent to that of the famous 
Crab Nebula, a supernova remnant that serves as a calibration target 
for high-energy observatories and is considered one of the brightest 
sources beyond the solar system at these energies. 

Even as it dimmed at higher energies, the nova brightened in the 
lower-energy, or softer, emissions detected by Swift's X-ray 
Telescope, a behavior typical of X-ray novae. By Wednesday, Swift 
J1745-26 was 30 times brighter in soft X-rays than when it was 
discovered and it continued to brighten. 

"The pattern we're seeing is observed in X-ray novae where the central 
object is a black hole. Once the X-rays fade away, we hope to measure 
its mass and confirm its black hole status," said Boris Sbarufatti, 
an astrophysicist at Brera Observatory in Milan, Italy, who currently 
is working with other Swift team members at Penn State in University 
Park, Pa. 

The black hole must be a member of a low-mass X-ray binary (LMXB) 
system, which includes a normal, sun-like star. A stream of gas flows 
from the normal star and enters into a storage disk around the black 
hole. In most LMXBs, the gas in the disk spirals inward, heats up as 
it heads toward the black hole, and produces a steady stream of 
X-rays. 

But under certain conditions, stable flow within the disk depends on 
the rate of matter flowing into it from the companion star. At 
certain rates, the disk fails to maintain a steady internal flow and 
instead flips between two dramatically different conditions -- a 
cooler, less ionized state where gas simply collects in the outer 
portion of the disk like water behind a dam, and a hotter, more 
ionized state that sends a tidal wave of gas surging toward the 
center. 

"Each outburst clears out the inner disk, and with little or no matter 
falling toward the black hole, the system ceases to be a bright 
source of X-rays," said John Cannizzo, a Goddard astrophysicist. 
"Decades later, after enough gas has accumulated in the outer disk, 
it switches again to its hot state and sends a deluge of gas toward 
the black hole, resulting in a new X-ray outburst." 

This phenomenon, called the thermal-viscous limit cycle, helps 
astronomers explain transient outbursts across a wide range of 
systems, from protoplanetary disks around young stars, to dwarf novae 
-- where the central object is a white dwarf star -- and even bright 
emission from supermassive black holes in the hearts of distant 
galaxies. 

Swift, launched in November 2004, is managed by Goddard Space Flight 
Center. It is operated in collaboration with Penn State, the Los 
Alamos National Laboratory in New Mexico and Orbital Sciences Corp. 
in Dulles, Va., with international collaborators in the United 
Kingdom and Italy and including contributions from Germany and Japan. 


For images related to this discovery and more information about Swift, 
visit: 

http://go.nasa.gov/QLlkCH 

	
-end-



To subscribe to the list, send a message to: 
hqnews-subscribe@xxxxxxxxxxxxxxxxxxxxxx
To remove your address from the list, send a message to:
hqnews-unsubscribe@xxxxxxxxxxxxxxxxxxxxxx

[Index of Archives]     [JPL News]     [Cassini News From Saturn]     [NASA Marshall Space Flight Center News]     [NASA Science News]     [James Web Space Telescope News]     [JPL Home]     [NASA KSC]     [NTSB]     [Deep Creek Hot Springs]     [Yosemite Discussion]     [NSF]     [Telescopes]

  Powered by Linux