Fastest known star

The search reveals the astonishing speed with which a star orbiting the supermassive black hole at the center of our galaxy, called Sagittarius A* (its name includes an asterisk), is moving just a short distance away.

Near Sagittarius A* is a very compact group of stars. This cluster, called the S cluster, hosts more than a hundred stars that vary in brightness and mass. S stars move very fast.

Through continuous improvement of analysis methods, along with observations spanning nearly twenty years, the international team of Florian Peissker of the University of Cologne in Germany has unambiguously identified a star in that constellation that orbits completely around Sagittarius A* in just four years.

A total of five telescopes observed the star, and four of these five were combined to form a large virtual telescope with which to make more precise and detailed observations.

The star S4716 orbits around Sagittarius A* at a speed of about 8000 kilometers per second. S4716 is within 100 AU of a black hole. This is just over three times the distance between Neptune and the Sun, or 100 times the distance between the Earth and the Sun.

2020 spotted S4716 and a few other stars in the S star cluster. (Photo: Universität zu Köln)

S4716’s orbit around Sagittarius A* is great for more than one reason. Stars cannot easily form near a black hole like this one. By force, S4716 had to form far away and then get closer to the black hole. The latter may have been caused by perturbations caused in its orbit by stars and other objects in the S group.

Bisker and colleagues present technical details of their discovery in The Astrophysical Journal, titled “Observing S4716 – a star with a 4-year orbit around Sgr A*.” (Line: NCYT by Amazings)