(picture by: J. Bergeron, Sky & Telescope Magazine)
The Rossi X-ray Timing Explorer has detected 'Quasi Periodic Oscillations' and flickering of the x-ray light from some neutron stars and this is seen as an indicator of how the gas is falling onto the surface of these dense collapsed bodies. Similar X-ray flickering has been claimed for a black hole, Cygnus X-1 and it may have a similar origin. By studying the changes in the timing of the x-ray flickering, astronomers have claimed to have seen the so-called Lenz-Thirring Effect of 'frame dragging', but these results are still tentative and a bit controvercial by 1999-2000. A blurb from Astronomy Picture of the day says the following:
Gravity can do more than floor you. According to recent measurements of a star system thought to contain a black hole, it can spin you too. This effect, called frame-dragging, is most prominent near massive, fast spinning objects. Now, a team led by W. Cui (MIT) has used the orbiting Rossi X-ray Timing Explorer to search for it near a system thought to contain a black hole. Cui's team claim that matter in this system gets caught up and spun around the black hole at just the rate expected from frame-dragging. Such discoveries help scientists better understand gravity itself.
GRO J1655-40 and GRS 1915+105 are superluminal jet sources ("microquasars") with compact objects that are postulated to be black holes spinning near the extreme theoretical limit. Frame dragging, a prediction of General Relativity, should cause the accretion disk to precess---an observable effect in RXTE data, according to the predictions of Wei Cui and colleagues. For GRO J1655-40, with both the black hole spin and mass (about 7 solar masses) known, the theoretically expected precession frequency of the inner portion of the accretion disk was calculated due to frame dragging. The result is ~300 Hz, which is precisely the observed frequency at which X-ray brightness varies nearly periodically.
Copyright 1997 Dr. Sten Odenwald
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