Astronomers are very confident that the
Milky Way galaxy has a supermassive black hole at its center, 26,000
light-years from the
Solar System, in a region called
Sagittarius A* because:
- The star S2 follows an elliptical orbit with a period of 15.2 years and a pericenter (closest distance) of 17 light-hours (7013180000000000000♠1.8×1013 m or 120 AU) from the center of the central object.
- From the motion of star S2, the object's mass can be estimated as 4.1 million M☉,[20][21] or about 7036820000000000000♠8.2×1036 kg.
- The radius of the central object must be less than 17 light-hours, because otherwise, S2 would collide with it. In fact, recent observations from the star S14 indicate that the radius is no more than 6.25 light-hours, about the diameter of Uranus' orbit. However, applying the formula for the Schwarzschild radius yields just about 41 light-seconds, making it consistent with the escape velocity being the speed of light.
- No known astronomical object other than a black hole can contain 4.1 million M☉ in this volume of space.
The
Max Planck Institute for Extraterrestrial Physics and
UCLA Galactic Center Group
[23] have provided the strongest evidence to date that Sagittarius A* is the site of a supermassive black hole,based on data from
ESO's
Very Large Telescope[24] and the
Keck telescope.
On 5 January 2015, NASA reported observing an
X-ray flare 400 times brighter than usual, a record-breaker, from
Sagittarius A*. The unusual event may have been caused by the breaking apart of an
asteroid falling into the black hole or by the entanglement of
magnetic field lines within gas flowing into Sagittarius A*, according to astronomers.
