In addition, the special theory of relativity, which explains why people traveling at different speeds see time and space differently, says that the speed of the star will cause the light to be bluer when moving toward us and redder when moving away. Nevertheless, the general theory of relativity says that the light it emits will lose energy and become redder by the time it reaches Earth, which is about 26,000 light years from the galactic center. The UC team followed the star SO-2, which is far enough from the event horizon to still be visible. (Video courtesy of Abhimat Gautam, Keck/UCLA Galactic Center Group) Taken by the Keck telescopes in Hawaii, these images pinpoint one star, SO-2, that in 2018 came close enough to the invisible black hole, called Sagittarius A* (Sgr A*), for astronomers to detect a gravitational redshift. Stars whip around the supermassive black hole in the center of our galaxy in this time-lapse video (looped 3 times) showing 24 years of images of the galactic center. The light falls back and orbits the black hole before eventually disappearing inside, so all we see is black. Redshift, blueshiftīlack holes are black because light emitted at the surface, or event horizon, cannot escape: It doesn’t have enough energy. Ghez, Lu, lead author Tuan Do of UCLA and their colleagues published their findings today in the journal Science. It cannot 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.” “However, his theory is definitely showing vulnerability. “We can absolutely rule out Newton’s law of gravity, (and) our observations are consistent with Einstein’s theory of general relativity,” said Ghez. The relativistic effects caused by the huge mass of the black hole allowed University of California astronomers to test Einstein’s special and general theories of relativity. At closest approach, the gravity is so great that light loses energy as it escapes. The speed-up as it approaches produces a blueshift in light from the star, while astronomers observe a redshift when it moves away. The 4 million-solar-mass black hole at the center of our galaxy warps spacetime, affecting the orbit of the star SO-2 when it gets near. “We know that, at some point, general relativity must break down, because it doesn’t mesh with quantum mechanics, so it is just a constant hunt for where that breaking point is,” Lu said. But tests around extremely massive objects - the black hole at the center of the galaxy is the mass of 4 million suns - could reveal where general relativity fails to explain the universe and modifications are necessary. General relativity, which treats gravity as a warping of space and time, has been validated within our solar system and in the interactions between pairs of dense, solar-mass neutron stars, or pulsars. It is almost impossible to do that in any other galaxy.” “Our galactic center is a special place, a unique place, because we can study in detail the physics and astrophysics of a supermassive black hole. “The measurement of gravitational redshift around a supermassive black hole is really the beginning of a new era of testing general relativity,” said Lu, who began working with Ghez as a graduate student in 2003. The effect, a gravitational redshift, matched exactly what Einstein’s theories of special and general relativity predict. The team, led by UCLA astronomer Andrea Ghez, and with key analyses by UC Berkeley’s Jessica Lu, an assistant professor of astronomy, followed a star orbiting so close to the black hole that the light it gives off is affected by the black hole’s intense gravity. University of California astronomers have tested Albert Einstein’s theories of relativity in the crucible of the monstrous black hole at the center of our Milky Way galaxy and found it rock solid. (National Science Foundation graphic by Nicolle R. As the star gets closer to the supermassive black hole, its light undergoes a gravitational redshift that is predicted by Einstein’s general theory of relativity. An artistic visualization of the star S0-2 as it passes by the supermassive black hole at the galactic center, which has warped the geometry of space and time.
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