S62 (star)

S62 is a star in the cluster surrounding Sagittarius A* (Sgr A*), the supermassive black hole in the center of the Milky Way. S62 orbits Sgr A* faster than any other star known as of August 2019. With an orbital period of only 9.9 years, it beats the previous record holder, the star S55, which circles Sgr A* in 12.8 years.[1]

In addition, S62 has a very eccentric orbit which makes it pass very close to Sgr A*, only 16 astronomical units (2400 million km), less than the distance between Uranus and the Sun. The star therefore passes only about 215 times the Schwarzschild radius of Sgr A* (the Schwarzschild radius of Sgr A* is approximately 0.082 AU, or 12 million km). It is closer to Sgr A* than the previous record, around 45 AU (6.7 billion km, 550 Schwarzschild radii) held by the star S175, and much closer than the more well-studied S2 (118 AU, 18 billion km, 1,440 Schwarzschild radii).[1]

S62 passes so close to Sgr A* that its orbit has a very large precession: its orbit shifts by about 10 degrees with each revolution. At closest approach its velocity is about 0.10c (10% of the speed of light) relative to Sgr A*. S62's next approach to Sgr A* is towards the end of 2022.[1]

The discovery of S62 improved the bounds on the mass distribution in the center of the galactic center, showing that (4.15±0.6)×10⁶ M_☉ are concentrated within 16 AU of the center, fully compatible with Sgr A* being a supermassive black hole.[1]

References

1. Peissker, Florian; Eckart, Andreas; Parsa, Marzieh (January 2020). "S62 on a 9.9 year orbit around SgrA*". The Astrophysical Journal. 889 (1): 61. arXiv:2002.02341. doi:10.3847/1538-4357/ab5afd.