Image: Frame-dragging
Einstein's general theory of relativity implies that massive, spinning objects like neutron stars and black holes distort space and time in their surroundings. This illustration shows how a black hole twists an imaginary grid of space and time.
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Massive objects like black holes and neutron stars appear to warp space and time in their surroundings, astronomers say in two new studies. The discovery gives a boost to Einstein’s general theory of relativity as well as to unorthodox “Star Trek” speculation.

The phenomenon observed by American and Italian astronomers is known as frame-dragging or Lense-Thirring precession.

As a consequence of Albert Einstein’s theories, physicists predicted in 1918 that the gravity of any spinning body should distort space and time in its surroundings, much like a twister picks up objects in their path. But the effect is so slight that it had never been detected in the more than seven decades since the prediction was first made.

Now American and Italian researchers say they have picked up evidence of the effect around black holes and fast-rotating neutron stars. Research papers on the subject were presented Nov. 6 at the American Astronomical Society’s High Energy Astrophysics Department meeting in Estes Park, Colo. Both studies cited observations made by NASA’s Rossi X-Ray Timing Explorer satellite.

“Although theorists predicted the frame-dragging effect, they didn’t have any observational evidence to prove it before the Rossi X-Ray Timing Explorer,” said Wei Cui of the Center for Space Research at the Massachusetts Institute of Technology, who led the American research team.

Black holes
The American researchers focused on black holes — huge stars that collapse into an object so massive and dense that nothing, not even light, can escape their gravitational pull. Such objects are detected only by their effect on nearby orbiting stars.

Spinning black holes may pull in gaseous matter from their sister stars as a rapidly rotating “accretion disk,” analogous to water circling down a bathtub drain.

The American scientists built on their previous research into the mass and spin of black holes to look for signs of space-time distortion, or frame-dragging.

In Einsteinian physics, the space-time continuum is often compared to a sheet of rubber. Mass creates a gravitational “dimple” in that space-time sheet. But a rotating object — like a spinning black hole — adds an extra twist to the dimple. Matter caught in that twist would appear to wobble in orbit around the object, like a toy top wobbling on its axis.

Cui explained that travelers passing close to a black hole would feel as if “nothing happened.” But a distant observer would see the travelers being dragged around the black hole.

Cui’s team looked at five black holes with spinning accretion disks. The scientists calculated how much the disks should wobble, based on the spin and mass of each black hole. And they found that in each case, the amount of observed wobble matched that predicted by Einstein’s gravitational theory. No other explanation could be applied to all five cases.

Cui’s collaborators in the study are Shuang Zhang of NASA’s Marshall Space Flight Center and Wan Chen of NASA’s Goddard Space Flight Center.

Neutron stars
Further confirmation came from the Italian study, which focused on X-ray observations of spinning neutron stars. Such stars are more massive than the sun, with a diameter of only about six miles. The gravitational attraction is so strong that disks of matter orbit the stars at about a third the speed of light, or 60,000 miles per second — and in the process those disks emit intense X-rays.

Luigi Stella of the Astronomical Observatory of Rome and Mario Vietri of the Third University of Rome found that powerful X-ray emissions from several spinning neutron stars appeared to fit the wobbling pattern predicted by the frame-dragging theory. Like Cui’s team, the Italians determined that other explanations for the wobble did not fit the data.

“We cannot be certain yet that the modulation we observe is due to the Lense-Thirring effect,” Vietri said in a news release. “More detailed observations and models are clearly required.”

Satellites such as NASA’s Gravity Probe B and the European-American LAGEOS III, both under development, are due to put delicate instruments into Earth orbit in hopes of detecting the frame-dragging effect closer to home.

The jump to hyperspace
On one hand, the new evidence represents merely one more step toward proving a long-accepted theory about the way the universe works. But on the other hand, space-time warps lead many people to think more seriously about warp drives, wormholes and other “Star Trek” devices for breaking the cosmic speed limit of 186,000 miles per second, the speed of light.

According to “Star Trek” lore, warp drives can propel a starship at faster-than-light speeds by moving a wrinkle of space-time containing the ship. Wormholes are supposedly tunnels in space-time that allow travelers to take an inter-dimensional express route between two distant locations.

Frederick Lamb, a physics and astronomy professor at the University of Illinois at Urbana-Champaign, says the latest findings could serve as an inspiration to future physicists and engineers — even if wormholes are little more than a scientific fantasy at this point in space-time.

Marc Millis of NASA’s Lewis Research Center is already involved in such ultralong-range issues as head of the space agency’s Breakthrough Propulsion Physics Program. The modestly funded program looks at exotic theories for propelling spacecraft without fuel, attaining speeds sufficient for interstellar travel and using unorthodox energy sources.

For Millis, the new findings about frame-dragging illustrate that “space-time itself is this beastie that’s more complex” than most people think.

Eventually, he said, spacecraft designers may be able to design a propulsion system that takes advantage of new cosmological principles.

“You need something to push against, and one thing to push against is space-time itself,” Millis said. “So the more you know about space-time and how it interacts with matter, the more clues you have to go in that direction.”

But Millis agreed with most cosmologists that “the wormholes and the warp drives are taking a huge leap of speculation of how much you can move it and what you can do with it. ... The causality violations end up being a whole separate question.”

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