Wrinkles in spacetime may reveal black holes

By Sara Goudarzi

Staff Writer

updated 1:50 p.m. ET Feb. 22, 2007

Seeing objects that don’t reflect light is tricky business. And black holes are as elusive as a target can be. The gravitational whirlwind of these cosmic wells draws inward with so much force that even light can’t escape their grasps.

This poses a tricky problem for scientists, whose instruments typically rely on light — whether it is visible light, radio waves, X-rays or infrared — to observe objects in space.

Astronomers currently spot black holes by detecting the high-energy radiation emitted by swirling matter falling into them. Before matter passes a black hole’s point of no return, called the event horizon, any radiation it emits can still escape. In a decade, however, scientists hope to spot black holes by looking at the warps in spacetime created by their immense gravity.

Researchers have known about black holes ever since their existence was predicted by theories such as Einstein’s general relativity. Knowing they are invisible, however, scientists have devised clever ways to detect the presence of black holes indirectly.

Peering inside the invisible
One method has been to watch the demise of an object falling into these cosmic graves.

“If material actually falls into a black hole, it gets shredded apart and it heats up,” said Roeland van der Marel, a researcher with the Space Telescope Science Institute.  “As it heats up, it starts emitting radiation, and this radiation we can observe.  In particular, we can often see X-rays coming from black holes.”

These X-rays do not penetrate the Earth’s atmosphere and can be detected only with telescopes positioned in space. NASA’s Constellation-X Observatory — a combination of four X-ray telescopes working together to generate 100 times the power of any X-ray satellite mission — will be able to perform such sensitive observations.

“The superior sensitivity of Con-X will give us enough information to be able to ask a fundamental question: Are black holes really described by (Einstein's theory)?” said Chris Reynolds, a Constellation-X science team member and a researcher at the University of Maryland. 

Observing neighbors to identify black holes
“In essence, Einstein's theory makes specific predictions about the way the X-ray spectrum changes in time as gas orbits around the black hole,” Reynolds told SPACE.com. “With Con-X, we can look for those variations in the spectrum and see if they match Einstein's predictions.”

Another technique used for identifying black holes is looking at how neighboring objects behave.

“Because a black hole is quite massive, any material, for example stars, that move close to it, will feel a lot of gravity,” van der Marel said.  “As a result of this, these stars will move quite fast. So another method of actually detecting the presence of black holes is looking for objects near the black hole that you can actually see that move much faster than you would naively have expected on the basis of the assumption that there would not be a black hole.”

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