GRS 1915+105

It was discovered on August 15, 1992 by the WATCH all-sky monitor aboard Granat. "GRS" stands for "GRANAT source", "1915" is the right ascension (19 hours and 15 minutes) and "105" reflects the approximate declination (10 degrees and 56 arcminutes). The near-infrared counterpart was determined by spectroscopic observations.

The binary system lies 11,000 parsecs away in Aquila. The black hole in GRS 1915+105 is 10 to 18 solar masses. The black hole rotates at least 950 times per second, giving it a spin parameter >0.82 (1.0 is the theoretical maximum).

Galactic superluminal source

In 1994, GRS 1915+105 became the first known galactic source that ejects material with apparent superluminal motion velocities.

Observations with high resolution radio telescopes such as VLA, MERLIN, and VLBI show a bi-polar outflow of charged particles, which emit synchrotron radiation at radio frequencies. These studies have shown that the apparent superluminal motion is due to a relativistic effect known as relativistic aberration, where the intrinsic velocity of ejecta is actually about 90% the speed of light.