[LINK] "Two Stars Do a Short-Orbit Tango Around the Milky Way’s Black Hole"

[rfmcdonald]

I'd heard of the star S2 or SO-2, orbiting the black hole at the centre of the Milky Way Galaxy from less than a light-day's distance and travelling at 2% of the speed of light in its orbit, before. Universe Today's Nancy Atkinson shares the news that astronomers have found a star in an even closer orbit. The implications for what is effectively our galaxy's biggest open-air physics laboratory is noteworthy.

Astronomers have known for some time there was one star orbiting fairly close to the black hole at the center of our galaxy. But now another star has been found dipping close and orbiting even faster around the Milky Way’s central black hole. Astronomer Andrea Ghez from UCLA says the ability to watch these two stars in a short-period ‘tango’ around the black hole will help scientist measure the effects of space-time curvature, and they should be able to determine whether Albert Einstein was right in his prediction of how black holes could warp space and time.

“I’m extremely pleased to find two stars that orbit our galaxy’s supermassive black hole in much less than a human lifetime,” said Ghez. “It is the tango of [these stars] that will reveal the true geometry of space and time near a black hole for the first time. This measurement cannot be done with one star alone.”

The previously known close-in star, S0-2, orbits the black hole every 15.5 years. And now, the newly found star, called S0-102, orbits the black hole in a blazing 11.5 years, the shortest known orbit of any star near this black hole.

In the same way that planets orbit around the sun, S0-102 and S0-2 are each in an elliptical orbit around the central black hole. Ghez said that the planetary motion in our solar system was the ultimate test for Newton’s gravitational theory 300 years ago, and now the motion of S0-102 and S0-2 will be the ultimate test for Einstein’s theory of general relativity, which describes gravity as a consequence of the curvature of space and time.

“The exciting thing about seeing stars go through their complete orbit is not only that you can prove that a black hole exists but you have the first opportunity to test fundamental physics using the motions of these stars,” Ghez said. “Showing that it goes around in an ellipse provides the mass of the supermassive black hole, but if we can improve the precision of the measurements, we can see deviations from a perfect ellipse — which is the signature of general relativity.”