An artist's impression of micro- quasar GRS 1915. Gas pulled from a companion star goes into a rapidly rotating disc around a black hole. A "wind" blowing off the disk interferes with a jet of gas and energy blowing away from the black hole.
Black hole caught in a tug of war
4 Apr 2009
New results from NASA's Chandra X-ray Observatory have made a major advance in explaining how a special class of black holes may shut off the high-speed energy streams they produce.
These results suggest that these black holes have an inbuilt mechanism for regulating the rate at which they grow.
Black holes come in many sizes. Supermassive ones, including those in quasars (galaxies with bright cores), weigh in at millions to billions of times the mass of the Sun. The much smaller stellar-mass black holes have measured masses in the range of about 7 to 25 times the Sun's mass.
Some stellar-mass black holes produce powerful streams or "jets" of particles and radiation, like those seen coming from quasars, and are called "micro-quasars".
The new study looks at a famous micro-quasar in our own Galaxy, and regions close to its event horizon, or point of no return. This system, GRS 1915+105 (GRS 1915 for short), contains a black hole about 14 times the mass of the Sun that is feeding off gas from a nearby companion star. As the material swirls toward the black hole, a build up known as an "accretion disc" forms.
The jet in this system shows remarkably unpredictable and complicated variability ranging from timescales of seconds to months, including 14 different patterns of variation. These variations are caused by a poorly understood connection between the accretion disc and the jet.
< The Chandra X-ray Observatory has studied the micro-quasar GRS 1915+105 eleven times since its launch in 1999.
Chandra has studied GRS 1915 eleven times since its launch in 1999. These observations reveal that the jet in GRS 1915 may be periodically choked off when a hot "wind", visible at X-ray wavelengths, is driven off the black hole's accretion disc.
The wind is believed to shut down the jet by depriving it of matter that would have otherwise fuelled it. Conversely, once the wind dies down, the jet can re-emerge.
"We think the jet and wind around this black hole are in a sort of tug of war," said Joseph Neilsen, Harvard graduate student and lead author of the paper appearing in the journal Nature. "Sometimes one is winning and then, for reasons we don't entirely understand, the other one gets the upper hand."
Although micro-quasars and bigger quasars differ in mass by factors of millions, they should show a similarity in behaviour when their very different physical scales are taken into account.
"If quasars and micro-quasars behave very differently, then we have a big problem to figure out why, because gravity treats them the same," said Neilsen.
Adapted from information issued by NASA / CXC / A. Hobart / Harvard / J. Neilsen.
LATEST HEADLINES & TOP STORIES:
> Black hole caught in a tug of war
> POSTCARD: Mars is the pits
> DOWN TO EARTH: Uluru (Ayers Rock) seen from space
> Hubble finds a hidden planet
> Galaxy survey shows where matter lurks
> DOWN TO EARTH: Great Britain and Ireland
> Meteorite impact helps trace asteroid origins
> Scientists find giant "twists" on the Sun
> DOWN TO EARTH: Africa's Atlas Mountains
> Does planet Earth have a twin?
> Scientists find clues to life in space
> DOWN TO EARTH: Lakes of Africa
> Spacewalks, space junk and dodgy plumbing
> Strange supernova queries theories
> Spokey Saturn
> A curious pair of galaxies
> Watch the space station on webcam!
> NASA's new rocket needs a super-chute
> DOWN TO EARTH: Volcanoes in Chile
> Pluto probe spots Neptune's major moon
> Saturn's ring-chomping moon
> MAIN NEWS PAGE…
Search SpaceInfo…
