The two telescopes on Mauna Kea observe the center of the Milky Way. The laser beams are needed to eliminate the distortions from the atmosphere. © Ethan Tweedie
The black hole in the center of the Milky Way apparently has company: The star S0-102 orbits the four million solar mass monster once in 11.5 years. This is the shortest known orbital period, as the discoverers around the Californian astronomer Leo Meyer now report. So far, astronomers have known only one star, which takes less than 20 years to orbit. The research team hopes to be able to use the two suns to verify some of the predictions of general relativity. The other star, directly in the center of the galaxy, S0-2, has a orbital period of 16 years. "It's 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, " says team leader Andrea Ghez. ? These measurements can not be done with a single star.? The general relativity theory of Albert Einstein states that large masses distort space-time. This slows down the flow of time and distances can be increased or decreased.

"Today is Einstein in every iPhone ?, says lead author Leo Meyer. "The GPS would not work without the theory of relativity." All tests in the solar system have so far passed the theory of relativity. But near a black hole, gravity is much stronger than in our immediate neighborhood. The researchers now want to find out whether the theory of relativity is valid under these extreme conditions.

The two stars S0-102 and S0-2 do not have round but elliptical orbits. If they reach the point with the shortest distance to the black hole on their orbit, the relativistic effects should become measurable, according to the thesis of the researchers. The star S0-2, which was discovered in 1995 and is 15 times as bright as the S0-102 now found, will reach this point in 2018. "If we observe the two stars over an entire cycle, can we first study fundamental physics near a black hole, " says Ghez. The team uses the powerful Keck telescope in Hawaii. With the adaptive optics method, astronomers can hide disturbing distortions through the Earth's atmosphere.

The fact that the two stars in the closer vicinity of a black hole, so to speak, in the death zone, on stable orbits, is surprising at first glance. But perhaps the dark Star Destroyers are less dangerous than previously thought. This is also shown in a recently published study by researchers led by Jay Strader of Michigan State University. They discovered two black holes near the center of the globular cluster M22. So far, astronomers had assumed that in such star clusters only a single black hole can survive. Because the previous research results had suggested that in many globular star clusters, numerous black holes weighing a few solar masses were born. In the course of time, when they sink into the center of the heap due to their mass, they inevitably get in each other's way, it has been said so far. In the end, only one black hole could be left? all others would either be thrown into space or melt together. display

"We searched for a black hole in the middle of the pile, but instead found two at a distance from the center, " says co-author James Miller-Jones of Curtin University in Australia. That means that theory and simulations need to be refined.

Perhaps even more black holes are hidden in the star cluster. Since they are only visible when they are devouring matter, could be stuck to the 100 more copies in the globular cluster, which belongs to the Milky Way. If globular clusters contain such large amounts of black holes, collisions between them could occur much more frequently than previously thought. Astronomers suspect that these gigantic events release gravitational waves? but according to them, detectors on earth have so far searched in vain.

Leo Meyer (University of California, Los Angeles) et al .: Science, Vol. 338, p. 84 Jay Strader (Michigan State University) et al .: Nature, Vol. 490, p. 71, doi: 10.1038 / nature11490 © science.de - Ute Kehse

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