S2 is a star orbiting the Sagittarius A* supermassive black hole with an orbital period of 16.0518 years. Sagittarius A* is an astronomical radio source, very dense and very bright, and it is the black hole at the center of the Milky Way. The radio source is located near the margin of two constellations, Sagittarius and Scorpius.
The significant of Sagittarius A* for scientists
Sagittarius A* is of great importance for astrophysicists. They rely on it to confirm, or infirm for that matter, Einstein’s theory of relativity in the most rigorous way possible. Since 1995, UCLA and the Max Planck Institute for Extraterrestrial Physics have designated each one a group to monitor S2 and the advances it makes while orbiting.
S2 is a Mercury-like star. It doesn’t keep the same trajectory while orbiting, it swings the path a little bit every time it retraces back the orbit. It is said that the perihelion is advancing. The perihelion is the closest point to the Sun it gets to during orbit. Mercury’s swing is more like a blues since its advancement is of only 43 seconds every century. This and the fact that, by 2008, S2 was observed performing only one complete orbit explain why it took 25 years for the two teams observing S2 have an answer.
The star orbiting the supermassive black hole proves Einstein’s General Relativity
The wait was worthwhile a quarter of a century. We know now that Einstein was right about Mercury, and that black holes do what he said they would do, and that Sagittarius A* is a massive black hole.
“Einstein’s General Relativity predicts that bound orbits of one object around another are not closed. One hundred years later we have the evidence that Sagittarius A* must be a supermassive black hole of 4 million times the mass of the Sun”, said Reinhard Genzel, Director at the Max Planck Institute for Extraterrestrial Physics.