Orbit Stars and Black Holes

Rosettenbahn around the black hole

The star S2 orbits the supermassive black hole in the center of the Milky Way exactly as predicted by general relativity. This is the conclusion of an international team of researchers after evaluating years of observations with the Very Large Telescope in Chile. The curvature of space-time caused by the strong gravity of the black hole twist the elliptical orbit into a rosette, the scientists report in the journal "Astronomy & Astrophysics".

For years, astronomers have followed the orbits of a good dozen stars in the vicinity of the central black hole in the galactic center. One of them - called S2 - is of particular interest to the researchers because it approaches the black hole closer to its orbit than any other. Reinhard Genzel from the Max Planck Institute for Extraterrestrial Physics in Garching and his colleagues have been targeting this star since 2016 with GRAVITY, among others. This instrument connects the four main telescopes of the Very Large Telescope and thus increases the spatial resolution many times over. In addition, the instrument is equipped with adaptive optics to compensate for disturbances in the earth's atmosphere - and it works in the near infrared range, which is particularly suitable for observing stars in the galactic center.

With GRAVITY, the astronomers working with Genzel succeeded in measuring the orbit of S2 with an accuracy of thirty micro-arcseconds - this corresponds to a distance of six centimeters on the surface of the moon. According to the high-precision measurements, the star's orbital ellipse rotates between 0.196 and 0.272 degrees per orbit. The general theory of relativity predicts a value of 0.202 degrees and thus agrees very well with the experimental value. So far, this effect - called Schwarzschild precession - could only be detected in our solar system and in some binary stars.