Star’s quick orbit offers glimpse into black hole

Scientists using the Keck Observatory atop Mauna Kea have found a second star in a remarkably fast orbit around the black hole at the center of the Milky Way galaxy.

The finding, published Thursday in the journal Science, may help astronomers discover whether Einstein was right in his fundamental prediction of how black holes warp space and time, said UCLA physicist Andrea Ghez, leader of the discovery team.

The star, known as S0-102, orbits the black hole in 11.5 years, a relative sprint that allows astronomers to study an entire orbit for perturbations that offer clues to the black hole’s structure.

Before this discovery, astronomers knew of only one star near the black hole with a very short orbit, S0-2, which completes a circuit in 16 years. Both are in the constellation Sagittarius.

"I’m extremely pleased to find two stars that orbit our galaxy’s supermassive black hole in much less than a human lifetime," Ghez said in a statement Thursday. "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."

She has been studying 3,000 stars that orbit the black hole, most of which have orbits of 60 years or longer.

S0-102 has the shortest known orbit.

"The pivotal research by Ghez’s UCLA group using the Keck Observatory has evolved from proving that a supermassive black hole exists in the center of our galaxy to testing the very fundamentals of physics," said Taft Armandroff, director of the Keck Observatory. "This is truly an exciting time in astronomy."

Black holes form out of the collapse of matter to such high density that not even light can escape their gravitational pull. They cannot be seen, but their influence on nearby stars is visible and provides a signature, said Ghez.

Leo Meyer, a researcher on Ghez’s team and lead author of the study, said, "Today, Einstein is in every iPhone, because the GPS system would not work without his theory. 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."