Researchers have discovered a star that whips around the giant black hole at the center of our galaxy in record time, completing an orbit every 11.5 years. The finding, appearing today in the journal Science, points ahead to groundbreaking experiments involving Einstein's general theory of relativity. Those tests will be fully enabled by the Thirty Meter Telescope (TMT), slated to begin observations next decade.
The record-setting star, called S0-102, was detected with the twin 10-meter telescopes at the W.M. Keck Observatory in Hawaii. For the past 17 years, the telescopes have imaged the galactic core, where a team of astronomers have hunted for stars with short orbital periods. These stars offer a never-before-possible test of how a supermassive black hole's gravity warps the fabric of space-time.
"The discovery of S0-102 is a crucial ingredient for our ultimate goal of revealing the fabric of space-time around a black hole for the first time," said Andrea Ghez, leader of the team and a professor of physics and astronomy at the University of California, Los Angeles and who is a member of the TMT project's Science Advisory Committee
Although Keck is among the most advanced astronomical instruments now in operation, it will require the future power of TMT and its adaptive optics system to put Einstein's theory through its paces.
"In order to test the heart of relativity, Einstein's equations, we have to wait for the next major technological breakthrough: TMT with its multi-conjugate adaptive optics system," said Leo Meyer, a member of Ghez' team and lead author of the new paper. Meyer, along with co-authors Sylvana Yelda and Tuan Do, is part of TMT's astrometry working group that studies the unique capabilities of TMT to observe the motion of the faintest objects in the universe.
"It is amazing to think about what TMT will be capable of," said Ghez.
TMT's adaptive optics system builds on those presently employed by premier observatories including Keck, Gemini, and the Very Large Telescope. Adaptive optics helps ground-based telescopes collect sharper images by compensating for the distorting effects of atmospheric turbulence. The systems rely on deformable mirrors and lasers that create "guide stars" in the sky to provide reference points for keeping observations in focus.
The adaptive optics designed for TMT, along with its huge primary mirror, will provide breakthroughs on many fronts, Ghez explained. On TMT, the angular resolution - the ability to see fine details - will be three times sharper than that of Keck. But the gain in astrometric, or tracking precision of individual stars in a crowded region like the center of our Galaxy will be at least a factor of 10. It is also conceivable that TMT will find stars that are even more tightly bound to the Milky Way's central black hole than S0-102.
Like Keck, TMT will track the motion of stars, such as S0-102, that have elliptical (oval-shaped) orbits. The orbits bring the stars periodically closer to the black hole. This proximity, coupled with TMT's precision, will allow for two key tests of relativity.
In the first, a star deep in the gravity well of a black hole should have its light be stretched out, or redshifted, to a certain degree, and have its orbit deviate from a perfect ellipse. A second aspect of the deviation should reveal that the stars' orbits experience precession, or a slight shifting, creating a flower-shaped pattern of orbits around the black hole over time. The deviations will speak to the validity of the actual equations underpinning general relativity.
Researchers know that at the heart of a black hole, Einstein's general theory of relativity should begin to break down. Should some of the results gleaned by TMT not match with the venerated theory, a new window would open into how gravity fundamentally works at all scales of the universe, from the grandest to the smallest.
"As strong a theory as general relativity is for large-scale phenomena, we do not know how to reconcile it with quantum mechanics, the theory that describes phenomena on atomic and subatomic scales," said Ghez. "One reason, therefore, that we want to build TMT is to delve into the most fundamental workings of our universe."
TMT is the next-generation astronomical observatory that is scheduled to begin scientific operations in 2021 on Mauna Kea, Hawaii. TMT is a collaboration of the California Institute of Technology, University of California, the Association of Canadian Universities for Research in Astronomy, the National Astronomical Observatory of Japan, a consortium of Chinese institutions led by the National Astronomical Observatories of the Chinese Academy of Sciences, and institutions in India supported by the Department of Science and Technology of India.