Bright blue giant stars can travel as fast as 8% of the speed of light

Sina science and technology news on August 18, Beijing time news, according to foreign media reports, in the center of the Milky way, there are hundreds of stars closely revolving around a supermassive black hole. The orbits of most of these stars are large enough that their motion conforms to Newton’s gravitational theory and Kepler’s law of motion. However, the orbits of a few stars are too close to the black hole, which can only be accurately described by Einstein’s general relativity. The star with the smallest orbit is called S62, which can travel more than 8% of the speed of light when it reaches the nearest black hole. < / P > < p > the supermassive black hole in the center of the Milky way is called Sagittarius A *, with a mass equivalent to 4 million suns. This is inferred from the stars that revolve around it. Astronomers have been tracking the movements of these stars for decades. By calculating their orbits, we can calculate the mass of a * black hole in Sagittarius. In recent years, as our observations have become more accurate, we can not only measure the mass of black holes, but also test our previous understanding of black holes. The most studied star around the a * black hole in Sagittarius is S2. It’s a bright blue giant star that orbits the black hole every 16 years. In 2018, S2 reached its closest point to the black hole, giving us an opportunity to observe one of the effects of relativity, gravitational redshift. If you throw a ball high, its speed will gradually slow down as it rises; but if you send a beam of light into the air, the speed of light will not slow down, but the energy of the light beam will be reduced under the action of gravity. Therefore, when the light beam climbs out of the “gravity well”, there will be a red shift. Scientists have observed this phenomenon in the laboratory before, but S2 gives us an opportunity to observe the red shift phenomenon in reality. At the closest point to the black hole, S2’s light does redshift as expected. For many years, scientists have believed that S2 is the nearest star to the a * black hole in Sagittarius. But a team recently discovered S62. The star, about twice the mass of the sun, orbits the black hole every 10 years. Their calculations show that when it reaches the closest point to the black hole, its speed can reach 8% of the speed of light. At such a high speed, the time expansion effect can not be ignored. One hour on S62 is about 100 minutes on earth. The orbit of S62 does not follow Kepler’s law because it is too close to the black hole. Its orbit is not a simple ellipse, but like a hula hoop, each turn will produce a 10 ° precession. This kind of relativistic precession was first observed in the orbit of mercury, but the effect of mercury orbit is not significant. In the autumn of 2022, S62 will again be close to the a * black hole in Sagittarius. Compared with S2, this close contact should help astronomers verify the relativistic effect more accurately. (leaf)