Indian origin astronomer probes violently variable black holes

Munich, Oct 16 : An astronomer of Indian origin and his team have used the VLT (Very Large Telescope) and Rossi XTE satellite to probe violently variable black holes, providing insights into the colossal energy that flows at their hearts.

By mapping out how well the variations in visible light match those in X-rays on very short timescales, astronomers have shown that magnetic fields must play a crucial role in the way black holes swallow matter.

Like the flame from a candle, light coming from the surroundings of a black hole is not constant - it flares, sputters and sparkles.

"The rapid flickering of light from a black hole is most commonly observed at X-ray wavelengths," said Poshak Gandhi, who led the international team that reports these results.

"This new study is one of only a handful to date that also explore the fast variations in visible light, and, most importantly how these fluctuations relate to those in X-rays," he added.

The observations tracked the shimmering of the black holes simultaneously using two different instruments, one on the ground and one in space.

The X-ray data were taken using NASA's Rossi X-ray Timing Explorer satellite. The visible light was collected with the high speed camera ULTRACAM, a visiting instrument at ESO's Very Large Telescope (VLT), recording up to 20 images a second.

ULTRACAM was developed by team members Vik Dhillon and Tom Marsh.

"These are among the fastest observations of a black hole ever obtained with a large optical telescope," said Dhillon.

To their surprise, astronomers discovered that the brightness fluctuations in the visible light were even more rapid than those seen in X-rays.

In addition, the visible-light and X-ray variations were found not to be simultaneous, but to follow a repeated and remarkable pattern: just before an X-ray flare the visible light dims, and then surges to a bright flash for a tiny fraction of a second before rapidly decreasing again.

None of this radiation emerges directly from the black hole, but from the intense energy flows of electrically charged matter in its vicinity.

The environment of a black hole is constantly being reshaped by a riotous melee of strong and competing forces such as gravity, magnetism and explosive pressure. As a result, light emitted by the hot flows of matter varies in brightness in a muddled and haphazard way.

"But the pattern found in this new study possesses a stable structure that stands out amidst an otherwise chaotic variability, and so, it can yield vital clues about the dominant underlying physical processes in action," said team member Andy Fabian.

ANI