Astronomers have announced the discovery of a remarkable star that orbits the supermassive black hole at the center of our galaxy in only 11.5 years – the shortest known orbit of any star near this black hole.
This Keck Observatory image shows the short-period star S0-102, the star S0-2 and the electromagnetic counterpart of the black hole, Sgr A* (L. Meyer et al)
“The star, known as S0-102, may help astronomers discover whether Albert Einstein was right in his fundamental prediction of how black holes warp space and time,” said co-author Andrea Ghez, a professor of physics and astronomy at the University of California Los Angeles (UCLA), who co-authored a paper in the journal Science (arXiv.org version).
Before this discovery, astronomers knew of only one star with a very short orbit near the black hole: S0-2, which Prof Ghez used to call her ‘favorite star’ and whose orbit is 16 years.
“I’m extremely pleased to find two stars that orbit our galaxy’s supermassive black hole in much less than a human lifetime,” said Prof Ghez, who studies 3,000 stars that orbit the black hole, and has been studying S0-2 since 1995. “Most of the stars have orbits of 60 years or longer.”
“It is the tango of S0-102 and S0-2 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.”
“Black holes, which form out of the collapse of matter, have such high density that nothing can escape their gravitational pull, not even light. They cannot be seen directly, but their influence on nearby stars is visible and provides a signature,” Prof Ghez explained.
Einstein’s theory of general relativity predicts that mass distorts space and time and therefore not only slows down the flow of time but also stretches or shrinks distances.
“Today, Einstein is in every iPhone, because the GPS system would not work without his theory,” said lead author Dr Leo Meyer of the University of California Los Angeles. “What we want to find out is, would your phone also work so close to a black hole? The newly discovered star puts us in a position to answer that question in the future.”
Over the past 17 years, the team has used the W.M. Keck Observatory to image the galactic center at the highest angular resolution possible.
“The Keck Observatory has been the leader in adaptive optics for more than a decade and has enabled us to achieve tremendous progress in correcting the distorting effects of the Earth’s atmosphere with high–angular resolution imaging,” Prof Ghez said. “It’s really exciting to have access to the world’s largest and best telescope. It is why I came to UCLA and why I stay at UCLA.”
“In the same way that planets orbit around the Sun, S0-102 and S0-2 are each in an elliptical orbit around the galaxy’s central black hole. The planetary motion in our Solar system was the ultimate test for Newton’s gravitational theory 300 years ago; the motion of S0-102 and S0-2,” she said, “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,” Prof Ghez said. “As the stars come to their closest approach, their motion will be affected by the curvature of spacetime, and the light traveling from the stars to us will be distorted.”
S0-2, which is 15 times brighter than S0-102, will go through its closest approach to the black hole in 2018.
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Bibliographic information: L. Meyer et al. 2012. The Shortest-Known–Period Star Orbiting Our Galaxy’s Supermassive Black Hole. Science, vol. 338, no. 6103, pp. 84-87; doi: 10.1126/science.1225506
