The Violent Variations of Black Holes
Written by Nancy Atkinson
What is the environment around a black hole really like? Astronomers are getting a better idea by observing the light coming from the accretion disk surrounding black holes. The light is not constant — it flares, sputters and sparkles – and this flickering provides new and surprising insights into the colossal amount of energy emanating from around black holes. 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.
"The rapid flickering of light from a black hole is most commonly observed at X-ray wavelengths," says 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."
The observations tracked the flickering 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," says 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.
Watch a movie of the fluctuations.
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 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," says team member Andy Fabian.
The visible-light emission from the neighborhoods of black holes was widely thought to be a secondary effect, with a primary X-ray outburst illuminating the surrounding gas that subsequently shone in the visible range. But if this were so, any visible-light variations would lag behind the X-ray variability, and would be much slower to peak and fade away. "The rapid visible-light flickering now discovered immediately rules out this scenario for both systems studied," asserts Gandhi. "Instead the variations in the X-ray and visible light output must have some common origin, and one very close to the black hole itself."
Strong magnetic fields represent the best candidate for the dominant physical process. Acting as a reservoir, they can soak up the energy released close to the black hole, storing it until it can be discharged either as hot (multi-million degree) X-ray emitting plasma, or as streams of charged particles travelling at close to the speed of light. The division of energy into these two components can result in the characteristic pattern of X-ray and visible-light variability.
Papers on this research: Here and Here
Source: ESO
Filed under: Black Holes
Related stories on Universe Today
Comment policy: Be nice and brief. Don't advertise your stuff, or promote your personal theories. We'll delete any comments that break these policies. Click here for more details.
October 15th, 2008 at 1:48 pm
In short…you wouldn't want live anywhere near one of these things.
October 15th, 2008 at 6:53 pm
Tell folks there's a Starbucks nearby and they'll flock to it anyway.
October 16th, 2008 at 1:13 am
Hey — maybe use a mini black hole for cockroach eradication! Nothing much else seems to work on the critters . . .
October 16th, 2008 at 8:18 am
Any chance this a young magnetar just settling in for a phase when rapidly varying Xray & visible light are to be expected as in the case of newly discovered SWIFT J1955 524106 and recently reported in Universe Today? The researchers noted "Strong magnetic fields represent the best candidate for the dominant physical process. Acting as a reservoir, they can soak up the energy released close to the black hole, storing it until it can be discharged either as hot (multi-million degree) X-ray emitting plasma, or as streams of charged particles travelling at close to the speed of light. The division of energy into these two components can result in the characteristic pattern of X-ray and visible-light variability". Again, might this be a nascent magnetar drawing material from its companion and strongly increasing the strength of its magnetic field, thus producing variability in its visible and Xray luminosity?
October 16th, 2008 at 8:37 am
Most articles about "visiting" a black hole focus on the event horizon and the inabiltiy to return, or the effects of gravity stretching one out like spagetti. But the X-Ray flux may well be lethal long before any human reaches those points. Given the measured X-Ray fluxes of these black holes, how close could one get before being "cooked"? I realize there's lots of variables in that question and that radiation absorption has to integrated with time. But assuming an unprotected human could get there, how close to a black hole would you have to be to receive 100 rems each second?
October 20th, 2008 at 9:02 pm
those black holes are so awsome!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1
November 16th, 2008 at 10:22 am
"Black hole sun won't you come, and wash away the rain? Black hole sun won't you come? Won't you come!" — Soundgarden