Newspaper article The Christian Science Monitor

Star Hurtling through Space near Humongous Black Hole Could Prove Einstein's Theory

Newspaper article The Christian Science Monitor

Star Hurtling through Space near Humongous Black Hole Could Prove Einstein's Theory

Article excerpt

Astronomers have found a star that breaks speed records as it orbits the Milky Way's central black hole, covering 3,100 miles (5,000 kilometers) per second as it whips around the black hole in less than a dozen years.

The discovery offers scientists a unique chance within the decade to test Einstein's theory of relativity in an extreme environment.

The star is named S0-102. It's one of a class of "S-stars" that surround the center of the sun's home galaxy in a kind of spherical shell. It has an orbital period of 11.5 years, give or take 3 1/2 months, making it the shortest-period star ever found in the region. The previous record was set by S0-2, which has a 16-year period.

The presence of two short-period stars means astronomers can look at the precession (change in orientation) of their orbits over time and use that information to learn how much space has been curved by the immense gravity of the galaxy's central black hole, which weighs in at 4 million times the sun's mass.

Such tests have been done before. The most famous study looked at the movement of the planet Mercury around the sun. Astronomers of the 19th century noticed Mercury's orbit was precessing more than could be accounted for by Newton's theory of gravity. At first they proposed the presence of another planet inside Mercury's orbit, but in the early 20th centuryEinstein was able to use his theory of relativity to predict exactly how much "extra" precession should happen as a result of space being curved by the sun's gravity, forcing the planet into a different path. [Photos: Black Holes of the Universe]

Other similar observations have been made of pairs of dense objects called neutron stars. However, because these stars can be only up to three times as massive as the sun, they don't curve space- time much more than the warping scientists see in the solar neighborhood.

Thus, studying the space-time around the Milky Way's gigantic black hole should offer an unprecedented test.

"This is the same idea in an unexplored parameter space," said Andrea Ghez, a professor of astronomy at the University of California, Los Angeles, and one of the leaders of the research team that found S0-102. "We know relativity breaks down on a small scale. We want to get as close to the event horizon as possible."

The event horizon around a black hole is the point of no return the closest anything can come without falling in.

The stars S0-102 and S0-2 appear to get fairly close. Their orbits are so near the central black hole that the effects of space- time curvature should be clearly visible. And the presence of these two short-period stars will allow observers to measure the local space-time curvature far more accurately than one star would.

The duo also helps astronomers take into account the fact that the gravitational mass of the central black hole isn't a perfect point; there are lots of other objects, such as remnants of dead stars, in the region that can cloud the observations. …

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