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MIT Scientists Find Evidence Of Long-Sought Space Warping

By K.C. Cole
Los Angeles Times

In a major confirmation of Einstein's theory of gravity, astrophysicists have seen evidence that space gets dragged around by spinning objects like the train of a wedding dress circling a twirling bride, astrophysicists announced Thursday at a meeting in Colorado. If correct, the findings pin down one of the final predictions of Einstein's theory - which forms the bedrock of physicists' understanding of all large scale events in the universe.

Other seemingly preposterous predictions of the theory that are now all but proven true include the existence of galaxy-size gravity lenses that bend starlight and black holes that suck in everything including light. Now, one of the last hold-outs - the idea that space itself gets swirled by spinning objects - appears to have been seen by researchers from the Massachusetts Institute of Technology and Rome 80 years after it was first proposed.

"It's taking what was science fiction and bringing it into everyday astronomy," said Michael Nowak, astrophysicist at the University of Colorado.

According to Einstein's theory of gravity, what people normally think of as empty space is actually a tightly woven fabric of space and time, interlocked like threads in a cloth. The space-time fabric gets warped by massive objects, just as a sheet would get warped into a deep well if an elephant were to sit on a bed. Anything that comes near the well naturally rolls in, and that "falling" is the force we perceive as gravity.

If the elephant twists around on the bed, his motion carries the sheet with him. And if Einstein's theory is correct, so should space-time be dragged around massive objects.

In the new work, the scientists report they were able to see evidence of this dragging by observing the behavior of cosmic behemoths like black holes and spinning stars.

Black holes - by definition - cannot be seen directly, as no light escapes their grasp. However, a visible companion orbiting near the black hole slowly gets sucked in by its immense gravity. The dust and gas get ripped off the star and swirl down into the hole, heating up to a billion degrees in the process and sending out an X-ray signal that can be decoded. Using the National Aeronautics and Space Administration's Rossi X-Ray Timing Explorer satellite scientists believe they saw convincing evidence for "frame dragging."

If the evidence for frame dragging bears out, it would give further strength to belief that Einstein's theory of gravity is right. "It's probably the biggest effect of Einstein's theories that hasn't been detected," said astrophysicist Lynn Cominsky of Sonoma State University, media spokeswoman for the meeting.

While Einstein's theory has passed all experimental tests "with flying colors," according to University of Illinois astrophysicist Frederick Lamb, "this is the first time we're entering the regime of very strong gravity."

The strongest gravitational fields encircle stars that have used up their nuclear fuel and collapse under their own weight. Some condense into neutron stars, so dense that a teaspoon would weigh millions of tons. Other, more massive stars, get squeezed to such extremes that they bend space-time into a black hole, from which nothing can escape.

The Rossi X-Ray satellite was launched by NASA in 1995 specifically to study such objects. Unlike the Hubble Space Telescope, the Rossi telescope does not take visible images. Instead, it detects energetic X-ray light coming from very close to the center of collapsed stars - within about 500 miles of the center.

Over the past year, researchers discovered that black holes and neutron stars sent out very regular X-ray signals, "like pure tones," Lamb said. The tones are probably caused by dense blobs of gas swirling around hundreds or thousands of times per second, like a lighthouse beacon. (By comparison, the Earth orbits the Sun only once a year).

Unexpectedly, these pure signals gave researchers a way to detect subtle wobbles that would indicate that space-time is being dragged. Just like a top wobbles as it gets dragged down by friction, so the orbiting blobs of gas would wobble as they drag space-time along with them.

Signals had been detected several years ago, but no one had looked for evidence of frame-dragging in them, partly because no one had thought it was possible to see them, said astrophysicist Luigi Stella of the Astronomical Observatory of Rome.

Stella and his colleagues calculated that if certain neutron stars were dragging space around them, their fluctuating X-ray signal should contain a second, slower, signal superimposed on the first. He saw such a motion in three of 15 stars he analyzed.

"The conclusion is that we are getting the first observational evidence of an effect that has been searched for for 80 years." he said.