This photo illustration shows the orbits of the stars S0-2 (in yellow) and S0-102 (in red) around the supermassive black hole at the center of the Milky Way. By studying the paths of the stars and how they deviate from traditional elliptical orbits, scientists hope to prove that Einstein’s general theory of relativity holds up in close proximity to the enormously powerful gravitational forces generated by black holes. Below, the Keck I (right) and Keck II telescopes at the summit of Mauna Kea utilize Laser Guide Star technology to paint reference points in the night sky to aid in capturing data with less atmospheric interference. (Photo illustration provided by W.M. Keck Observatory/HTH)
If famed physicist Albert Einstein were still alive, he’d likely be thrilled to be atop Mauna Kea tonight.
That’s because University of California, Los Angeles astronomers utilizing telescopes at Hawaii Island’s W.M. Keck Observatory reported Thursday their discovery of a star that could hold the key to proving whether Einstein was right when he described how black holes warp space and time.
The star, known as S0-102, is remarkable in that it is caught in a relatively close orbit around a gigantic black hole at the center of the Milky Way galaxy, revolving around it every 11.5 years — the shortest orbital period of any star near the black hole.
It joins another star with a very short orbital period: S0-2, which revolves around the black hole once every 16 years. Most of the other 3,000 stars in orbit around the black hole take 60 years or longer to traverse the great distances around it, making them more difficult for scientists to observe through complete or multiple orbits, said Andrea Ghez, leader of the UCLA discovery team and professor of physics and astronomy. She is also a co-author of a research paper announcing the discovery of S0-102, which was published Friday in the journal Nature.
“I’m extremely pleased to find two stars that orbit our galaxy’s supermassive black hole in much less than a human lifetime,” said an emailed statement from Ghez, who has been studying S0-2 since 1995.
Black holes form as matter collapses in on itself, forming regions of such intensely high density that nothing can escape their gravitational pull, including light. Because of this ability to swallow light, black holes are difficult to observe, but their influence on nearby stars leaves telltale signals, Ghez explained.
“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 said. “This measurement cannot be done with one star alone.”
Leo Meyer, a researcher on Ghez’s team and lead author of the study, explained that Einstein’s theories make possible technologies such as the global positioning systems found in modern consumer electronics like the iPhone.
“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,” he said.
Ghez added that measurements taken as the two stars revolve around the black hole are expected to reveal a great deal of information, including how black holes grow over time, the role supermassive black holes play in the center of galaxies, and whether Einstein’s theory of general relativity is valid near a black hole, where it has yet to be tested.
“It’s exciting to now have a means to open up this window,” she said.
As the stars come to their closest approach to the black hole within their elliptical orbits, their motion will be affected by the curvature of space-time, as predicted by Einstein’s general theory of relativity, and the light traveling from the stars to observers on Earth will be distorted, Ghez said.
“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,” she said.
S0-2, which is 15 times brighter than S0-102, will go through its closest approach to the black hole in 2018.
It was Ghez and her team who initially proved in 1998, through their use of the Keck Observatory, that an enormous black hole with a mass 4 million times that of the sun resides at the center of our galaxy. Physicists had debated its existence for more than 25 years.
For the past 17 years, she and her colleagues have utilized the facility’s telescopes outfitted with a powerful technology they helped to pioneer, called adaptive optics, to produce images of the Milky Way’s center at the “highest angular resolution possible,” according to a press release issued by the observatory.
Peter Wizinowich, Keck’s principal investigator for adaptive optics, said Friday he was thrilled with the team’s discovery, and he relishes the opportunities he has at the observatory to work on a wide variety of research projects with a number of the world’s top scientists.
“To me personally, it’s just such a unique laboratory to be working in,” he said. “There’s been such a huge revolution (because of adaptive optics). It’s letting us be able to see much closer to the birth of the universe.”
Essentially, he explained, adaptive optics allow scientists to capture clearer images as they are taken through the Earth’s atmosphere. The system measures distortions in wavelengths of light as they pass through the atmosphere, and then adjusts the telescope mirrors to adapt to the distortions.
Over the 21 years Wizinowich has spent at Keck, he says he’s been a part of helping the system adapt and grow, continually improving the quality of data scientists have at their disposal. An important improvement necessary for Ghez’s research was the telescope’s Laser Guide Star system, which paints a point about 90 kilometers above the Earth, to provide a reference point to aid the telescope’s adaptive optics in clearing up distortions.
The Laser Guide Star system was necessary for Ghez’s research because the center of the Milky Way is relatively dark, with few bright stars to act as their own reference points for the adaptive optics.
“The kind of precision they’re interested in (for this research) is pretty tight,” he said.
Wizinowich added that he and his colleagues will have to continue to improve the quality of the data they are able to pull from the telescopes, and Ghez and her team will have to continually improve the way they combine and translate that data if they are to answer the fundamental questions at the center of the research project.
“We can maybe make the measurement, but the level of confidence in the measurement, we want to improve that,” he said. “We always want to be learning, and taking that knowledge and making an improved system.”