Black holes that can regulate the rate at which they grow

March 26th, 2009 - 2:18 pm ICT by ANI  

Washington, March 26 (ANI): New results from NASA’s Chandra X-ray Observatory have suggested that a special class of black holes have a mechanism for regulating the rate at which they grow, and can shut off the high-speed jets they produce.

Some stellar-mass black holes launch powerful jets of particles and radiation, like seen in 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 material from a nearby companion star.

As the material swirls toward the black hole, an accretion disk forms.

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 disk and the radio jet seen in GRS 1915.

Chandra, with its spectrograph, has observed GRS 1915 eleven times since its launch in 1999.

These studies reveal that the jet in GRS 1915 may be periodically choked off when a hot wind, seen in X-rays, is driven off the accretion disk around the black hole.

The wind is believed to shut down the jet by depriving it of matter that would have otherwise fueled 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 research paper. “Sometimes one is winning and then, for reasons we don’t entirely understand, the other one gets the upper hand,” he added.

The latest Chandra results also show that the wind and the jet carry about the same amount of matter away from the black hole.

This is evidence that the black hole is somehow regulating its accretion rate, which may be related to the toggling between mass expulsion via either a jet or a wind from the accretion disk.

Self-regulation is a common topic when discussing supermassive black holes, but this is the first clear evidence for it in stellar-mass black holes.

According to Julia Lee, assistant professor in the Astronomy department at the Harvard-Smithsonian Center for Astrophysics, “It is exciting that we may be on the track of explaining two mysteries at the same time: how black hole jets can be shut down and also how black holes regulate their growth.” (ANI)

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