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Einstein's General Relativity Theory Beginning to Fray at the Edges

 Einstein's General Relativity Theory is Still Stands for Now

A star known as S0-2 (the blue and green object in this artist's rendering) made its closest approach to the supermassive black hole at the center of the Milky Way in 2018.

More than 100 years after Albert Einstein published his iconic general theory of relativity, it is beginning to fray at the edges, said Andrea Ghez, UCLA professor of physics and astronomy. Now, in the most comprehensive test of general relativity near the monstrous black hole at the center of our galaxy, Ghez and her research team report July 25 in the journal Science that Einstein's theory holds up

" Einstein's right, at least for now, "said Ghez, co-lead author of the research. "We can absolutely rule out Newton's law of gravity. Our observations are consistent with Einstein's general theory of relativity. However, his theory is definitely showing vulnerability. It can not fully explain gravity inside a black hole, and at some point we will need to move beyond Einstein's theory to a more comprehensive theory of gravity that explains what a black hole is. "

 Einstein's General Relativity Theory is Questioned

Star orbiting supermassive black hole. Nicole Fuller / National Science Foundation

Einstein's 1915 general theory of relativity holds that what we perceive as the force of gravity arises from the curvature of space and time. The scientist proposed that objects such as 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 has made direct measurements of the phenomenon near a supermassive black hole-research Ghez describes as "extreme astrophysics."

Animation by Zina Deretsky / National Science Foundation [19659004] Ghez's research team was able to see the co-mingling of space and time near the supermassive black hole. "In Newton's version of gravity, space and time are separate, and do not co-mingle; under Einstein, they get completely co-mingled with a black hole, "she said.

" Making a measurement of such fundamental importance has required years of patient observation, enabled by state-of-the-art technology, "said Richard Green, director of the National Science Foundation's division of astronomical sciences. For more than two decades, the division has supported Ghez, along with several of the technical elements critical to the research team's discovery. "Through their rigorous efforts, Ghez and her collaborators have produced a high-level validation of Einstein's idea of ​​strong gravity."

Keck Observatory Director Hilton Lewis called Ghez "one of our most passionate and tenacious Keck users." groundbreaking research, "he said," is the culmination of unwavering commitment over the past two decades to unlock the mysteries of the supermassive black hole in the center of our Milky Way galaxy. "

The researchers studied photons – particles of light – as they traveled from S0-2 to Earth. S0-2 moves around the black hole at blistering speeds of more than 16 million miles per hour at its closest approach. Einstein had reported that in this region close to the black hole, photons have to do extra work. Their wavelength as they leave the star depends not only on how fast the star is moving, but also on how much energy the photons spend to escape the black hole's powerful gravitational field.

 Einstein's General Relativity Theory Still Stands


Ghez was given the opportunity to present partial data last summer, but chose not to so her team could thoroughly analyze the data first. "We're learning how gravity works. It's one of four fundamental forces and we've tested the least, "she said. "There are many regions where we just have not asked, how does gravity work here? It is easy to be overconfident and there are many ways to misinterpret the data, many ways that small errors can accumulate in significant errors, which is why we did not rush our analysis. "

Ghez, and 2008 recipient of the MacArthur" Genius "Fellowship, studies more than 3,000 stars that orbit the supermassive black hole. Hundreds of them are young, she said, in a region where astronomers did not expect them to see.

It takes 26,000 years for the photons from S0-2 to reach Earth. "We're so excited and have been preparing for years to make these measurements," said Ghez, who directs the UCLA Galactic Center Group. "For us, it's visceral, it's now – but it actually happened 26,000 years ago!"

This is the first of many tests of general relativity Ghez's research team will conduct on stars near the supermassive black hole. Among the stars that most interest is S0-102, which has the shortest orbit, taking 11 1/2 years to complete a full orbit around the black hole.

The Ghez team took measurements about every four nights during crucial periods in 2018 using the Keck Observatory – which sits atop Hawaii's dormant Mauna Kea volcano and houses one of the world's largest and premier optical and infrared telescopes. Measurements are also taken with an optical-infrared telescope at Gemini Observatory and Subaru Telescope, also in Hawaii. She and her team have used these telescopes both on site in Hawaii and remotely from an observation room at UCLA's Department of Physics and Astronomy.

Black holes have such high densities that nothing can escape their gravitational pull, not even light. (They can not be seen directly, but their influence on nearby stars is visible and provides a signature.) Once something crosses the "event horizon" of a black hole, it will not be able to escape. (19659004) Ghez's co-authors include Tuan Do, lead author of the Science paper, and UCLA research scientist and deputy director of the paper. UCLA Galactic Center Group; Aurelien Hees, and former UCLA postdoctoral scholar, now a researcher at the Paris Observatory; Mark Morris, UCLA professor of physics and astronomy; Eric Becklin, UCLA professor emeritus of physics and astronomy; Smadar Naoz, UCLA assistant professor of physics and astronomy; Jessica Lu, and a former UCLA graduate student who is now a UC Berkeley assistant professor of astronomy; UCLA graduate student Devin Chu; Greg Martinez, UCLA project scientist; Shoko Sakai, and UCLA research scientist; Shogo Nishiyama, associate professor of Japan's Miyagi University of Education; and Rainer Schoedel, a researcher with the Spanish Institute of Astrophysics of Andalucia.

The National Science Foundation has funded Ghez's research for the past 25 years. More recently, her research has also been supported by the 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 responded to one of the most important questions in astronomy, helping to show that a supermassive black hole resides in the center of our Milky Way galaxy.

A powerful technology that Ghez helped to pioneer, called adaptive optics, corrects the distorting effects of Earth's atmosphere in real-time. With adaptive optics at Keck Observatory, Ghez and her colleagues have revealed many surprises about the environments surrounding supermassive black holes. For example, they discovered young stars where no one was expected to be seen and a lack of old stars where many were anticipated. It is unclear whether S0-2 is young or just masquerading as a young star, Ghez said.

In 2000, she and colleagues reported that for the first time, astronomers had seen stars accelerate around the supermassive black hole. In 2003, Ghez reported that the case for the Milky Way's black hole had been significantly strengthened and that all of the proposed alternatives could be excluded.

In 2005, Ghez and her colleagues took the first clear picture of the center of the Milky Way, including the area around the black hole at Keck Observatory. And in 2017, Ghez's research team reported that S0-2 does not have a companion star, solving another mystery

Publication: Tuan Do, et al., "Relativistic redshift of the star S0-2 orbiting the Galactic Center supermassive black sticks, "Science 16 Aug 2019: eaav8137; DOI: 10.1126 / science.aav8137

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