More than 100 years after Albert Einstein published his iconic Theory of General Relativity, it begins to break on the edges, said Andrea Ghez, Professor of Physics and Astronomy at UCLA. Now Ghez and her research team report in the most comprehensive general relativity test near the monstrous black hole (19459007) in the center of our galaxy on July 25 in the journal Science that Einstein's theory holds true.
At least for the moment, Einstein is right, "said Ghez, co-lead author of the study. "We can absolutely rule out Newton's law of gravity. Our observations are consistent with Einstein's general theory of relativity. His theory, however, definitely shows vulnerability. It can not fully explain gravity in a black hole, and eventually we need to go beyond Einstein's theory to a more comprehensive theory of gravity that explains what a black hole is.
Einstein's general theory of relativity in 1915 states that what we perceive as gravity arises from the curvature of space and time. The scientist suggested that objects like the sun and the earth change this geometry. Einstein's theory is the best description of how gravity works, said Ghez, whose UCLA-led team of astronomers directly measured the phenomenon near a supermassive black hole. The research that Ghez calls "extreme astrophysics."
Andrea Ghez: Feel the gravitational force of gravity. Video by Julie Winokur
The laws of physics, including gravity, should apply throughout the universe, Ghez said, adding that her research team is one of only two groups in the world to observe a star, the as known, S0-2 orbits the supermassive black hole in the middle of the Milky Way in three dimensions. The entire orbit takes 16 years, and the mass of the black hole is about 4 million times that of the sun.
The researchers say that their work is the most detailed study ever conducted on the supermassive black hole and Einstein's general theory of relativity.  The key data of the research were spectra that Ghez & # 39; team analyzed in April, May and September when their "favorite star" approached the huge black hole nearest. Spectra, which Ghez called the "rainbow of light" of stars, show the intensity of the light and provide important information about the star from which the light emanates. The spectra also show the composition of the star. These data have been combined with measurements Ghez and her team have performed over the past 24 years.
Spectra – collected at the W.M. The Keck Observatory in Hawaii uses a spectrograph built by a team led by colleague James Larkin at UCLA – showing the star's motion in unprecedented precision. (The other two dimensions are picked up by the researchers at the Keck Observatory.) Larkin's instrument picks up and distributes light from a star, much like raindrops scatter light from the sun to create a rainbow, Ghez says.
] "What is special about S0-2 is that we have a full orbit in three dimensions," said Ghez, who holds the Chair of Astrophysics for Lauren B. Leichtman and Arthur E. Levine. "That's what gives us the ticket to General Relativity testing, asking how gravity behaves near a supermassive black hole, and whether Einstein's theory tells us the full story." Traversing the entire orbit of stars offers the first way to test basic physics based on the motion of these stars. "
Animation by Zina Deretsky / National Science Foundation  Ghez's research team was able to blend space and time near the supermassive black hole In Newton's version of gravity, space and time are separate and do not mix, and under Einstein they completely mingle near a black hole. "
" Measurement of such fundamental importance requires years of patient observation, enabled by the state of the art, "said Richard Green, director of the astronomical department Sciences of the National Science Foundation. For more than two decades, the Ghez department has been supporting several technical elements critical to the discovery of the research team. "Through their rigorous efforts, Ghez and her associates have endorsed Einstein's belief in strong gravity of high importance."
Hilton Lewis, director of the Keck Observatory, named Ghez "one of our most passionate and toughest Keck users." Breakthrough research, "he said," is the culmination of the unwavering commitment of the last two decades to decipher the secrets of the supermassive black hole at the center of our Milky Way galaxy.
The researchers studied photons – light particles – as they traveled from S0-2 to Earth, S0-2 moving around the black hole at a speed of more than 25 million km / h on its next approach. Photons do extra work in this region near the black hole, and their wavelength as they leave the star depends not only on how fast the star moves, but also on how much energy the photons spend in the strong gravitational field Gravity is much stronger in the vicinity of a black hole than on Earth.
Ghez received the opportunity to submit subdivisions last summer However, against this, her team could do this by analyzing the data thoroughly. "We learn how gravity works. It's one of four fundamental forces and the ones we've least tested, "she said. "There are many regions where we did not ask how gravity works here, it's easy to be cocky, and there are many ways to misinterpret the data, many ways in which small mistakes can lead to significant mistakes That's why we did not accelerate our analysis. "[Ghezrecipientofthe2008MacArthur"Genius"Fellowship"examinesmorethan3000starsorbitingthesupermassiveblackholehundredsofthemareyoungshesaidRegionwhereastronomerswouldnothaveexpectedit
It takes 26,000 years for the photons from S0-2 to reach Earth. "We are so excited and have spent years preparing to take these measurements," Ghez said. Head of the UCLA Galactic Center Group. "It's visceral to us, it's now – but it actually happened 26,000 years ago!"
This is the first of many general tests The theory of relativity that Ghez & # 39; s research team performs on stars near the supermassive black hole. Among the stars that most interest them is S0-102 with the shortest orbit that takes 11 1/2 years to complete a full orbit around the black hole. Most stars that Ghez explores have orbits that are much longer than a human lifetime.
Ghez & # 39; s team measured the Keck Observatory roughly every four nights in critical periods on Hawaii's dormant Mauna Kea volcano in 2018, and one of the two houses the world's largest and leading optical and infrared telescopes. The measurements are also carried out with an optical infrared telescope at the Gemini Observatory and Subaru Telescope, also in Hawaii. She and her team used these telescopes both on-site in Hawaii and remotely from an observation room in the Department of Physics and Astronomy at UCLA.
Black holes are so dense that nothing can escape their attraction, not even light. (They can not be seen directly, but their influence on nearby stars is visible and provides a signature.) Once something goes beyond the "event horizon" of a black hole, it can not escape, but the star S0-2 is still there Event horizon, even if it comes closest to it, its photons are not drawn in.)
Ghez's co-authors include Tuan Do, lead author of the Science Paper, a UCLA researcher and deputy director of the UCLA Galactic Center Group; Aurelien Hees, former UCLA postdoctoral researcher, now researcher at the Paris Observatory; Mark Morris, UCLA Professor of Physics and Astronomy; Eric Becklin, Emeritus Professor of Physics and Astronomy at UCLA; Smadar Naoz, UCLA Assistant Professor of Physics and Astronomy; Jessica Lu, a former graduate of UCLA who now works as assistant professor of astronomy at UC Berkeley; Devin Chu, graduate student of UCLA; Greg Martinez, UCLA Project Scientist; Shoko Sakai, a UCLA scientist; Shogo Nishiyama, associate professor at the Japanese Miyagi University of Education; and Rainer Schoedel, a researcher from the Spanish Instituto de Astrofısica de Andalucıa.
The National Science Foundation has funded Ghez's research over the last 25 years. More recently, her research has also been researched by W.M. Keck Foundation, the Gordon and Betty Moore Foundation, and the Heising-Simons Foundation; as well as Lauren Leichtman and Arthur Levine and Howard and Astrid Preston.
In 1998, Ghez answered one of the most important questions in astronomy and helped to show that a supermassive black hole is at the center of our galaxy galaxy. The question had been the subject of intense debate among astronomers for more than a quarter of a century.
A powerful technology, which Ghez calls adaptive optics, corrects the distorting effects of Earth's atmosphere in real time. With the adaptive optics at the Keck Observatory, Ghez and her colleagues have revealed many surprises regarding the environment of supermassive black holes. For example, they discovered young stars that were not expected, and a lack of old stars, many of which were expected. It's unclear whether S0-2 is young or disguised as a young star, Ghez said.
In 2000, she and colleagues reported that for the first time astronomers had seen stars accelerating around the supermassive black hole. In 2003 Ghez reported that the case for the Black Hole in the Milky Way had been significantly strengthened and all proposed alternatives could be excluded.
In 2005, Ghez and her colleagues made the first clear picture of the center of the Milky Way, including the Black Hole area, at the Keck Observatory. In 2017, the Ghez research team reported that S0-2 has no companion star, which solves another puzzle.
Publication: Tuan Do et al., Relative Redshift of the Star S0-2 Orbiting the Galactic Center in Supermassive Black Hole, Science Aug. 16, 2019: eaav8137; DOI: 10.1126 / science.aav8137