Find the nearest star to the central black hole in the galaxy

An international team of researchers, with Spanish contribution, has found the closest star to Sagittarius A *, the black hole four million times the mass of the Sun located in the center of the Milky Way. It is the star S0-102; it takes 11.5 years to complete one orbit around the black hole. The work will know how to operate the law of gravity in extreme environments, according to the journal Science.

"So far only knew a star orbiting Sagittarius A *: S0-2, it takes to complete one orbit cuyoestudio 16.2 years and allowed us to measure the mass of the black hole four million solar masses," says Schodel Rainer, co-author, who works at the Institute of Astrophysics of Andalusia, CSIC. Now, thanks to this new finding, not only know two stars with orbits near Sagittarius A *, but also get to test the theory of general relativity under conditions of extreme gravity, "he adds.

The detection of the star was made ​​possible file au n high resolution images obtained by the WM Keck Observatory on Mauna Kea (Hawaii) over the past 17 ​​years and a new image analysis method Schodel developed to detect stars which were too weak and went unnoticed. "With this new technique we could detect S0-102 in an image taken about ten years ago and follow it along its orbit," the CSIC researcher.

The General Relativity suggests that the geometry of space-time is not rigid, but the presence of matter produces a modification and, more specifically, the "curve" in the vicinity of the objects. This curvature is causing gravitational effects that govern the motion of bodies, both of the planets around the sun like galaxy clusters. Supermassive black holes are an ideal environment to verify this effect.

The star S0-2 and S0-102 draw elliptical orbits around Sagittarius A *, so that every so often they are exceptionally close to the black hole. It is believed that, under these circumstances, its movement is affected by the intense curvature of spacetime produced by Sagittarius A *, which causes, among other things, that its orbit does not end up closed, but open trace an ellipse.

"Measuring the effects of gravity on stellar orbits is very interesting because gravity is the least known of the four fundamental forces," said Schodel. The environment of Sagittarius A *, with thousands of stars and stellar remnants, it was difficult because the mass of those bodies, undetectable with current telescopes, also contributes to changes in the orbit. "In order to disentangle the different effects, the General Relativity and the mass around Sagittarius A *, it took at least two stars that can be measured with high accuracy," says CSIC researcher.