Scientists Nudge Closer to the Edge of a Black Hole
The observations include clocking the speed of a black hole's spin rate
and measuring the angle at which matter pours into the void, as well
as evidence for a wall of X-ray light pulled back and flattened by gravity.
"Across the board, we are finding the broad iron K line to be an
incredibly robust measure of black hole properties," said Andrew
Fabian of Cambridge University, England, who led one of the teams. "We
are entering the era of precision black hole measurements."
Suzaku contains a high-energy X-ray detector and an X-ray spectrograph.
Together, these instruments detect a broad range of X-ray energies, particularly
the higher X-ray energies. Supermassive black holes are a prime target.
These are objects in the center of most galaxies, containing the mass
of millions to billions of suns confined within a region about the size
of our solar system.
Scientists can discern whether a black hole is spinning or not by studying the matter and energy around the black hole. If the black hole is spinning, matter can orbit more tightly. This is called the "innermost stable circular orbit," the closest you can get to a black hole without falling in. The faster the black hole spins, the tighter the orbit. Because gravity is stronger closer to the black hole, light is stretched more. So a spinning black hole has a spectrum that's "broader" --- a reflection of iron gas that usually emits X-rays at 6.4 kiloelectron volts but instead is broadened or stretched to lower energies. How low and how broad is a reflection of how fast the black hole is spinning and how close matter gets to it.
In a galaxy called
MCG-6-30-15, Fabian's group confirmed that the central black hole
is spinning rapidly, taking space and time along for a ride
with it. The group found evidence that X-rays emitted close to the
black hole, trying to escape, are bent back into the disk of matter
inward, away from us. This is predicted by Einstein's general relativity,
hinted at in earlier observations, but seen in remarkable new detail
Launched in 2005, Suzaku is the fifth in a series of Japanese satellites devoted to studying celestial X-ray sources and is managed by the Japan Aerospace Exploration Agency (JAXA). This mission is a collaborative effort between Japanese universities and institutions and NASA Goddard, which provided the X-ray mirrors.