GRS 1915+105
First galactic source with apparent superluminal jet motion.
GRS 1915+105, also designated V1487 Aquilae, is an X-ray binary star system located 11,000 parsecs away in the constellation Aquila. It contains a main sequence star and a black hole, with material transfer from the star to the black hole generating a relativistic jet, making it a microquasar system. The jet exhibits apparent superluminal motion, and in 1994 it became the first known galactic source to eject material with such apparent velocities.
- Discovery date
- August 15, 1992
- Discovery instrument
- WATCH all-sky monitor aboard Granat
- Distance
- 11,000 parsecs
- Black hole mass
- 10 to 18 solar masses
- Black hole rotation rate
- at least 950 times per second
- Spin parameter
- >0.82
- Intrinsic jet velocity
- about 90% the speed of light
Lore & Background
GRS 1915+105 was discovered on August 15, 1992 by the WATCH all-sky monitor aboard the Granat satellite. The designation 'GRS' stands for 'GRANAT source', '1915' indicates 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 black hole in the system has a mass of 10 to 18 solar masses and rotates at least 950 times per second, giving it a spin parameter greater than 0.82, where 1.0 is the theoretical maximum.
In 1994, GRS 1915+105 became the first known galactic source that ejects material with apparent superluminal motion velocities. High-resolution radio observations with telescopes such as VLA, MERLIN, and VLBI reveal a bi-polar outflow of charged particles emitting synchrotron radiation at radio frequencies. These studies show that the apparent superluminal motion is due to relativistic aberration, with the intrinsic velocity of the ejecta being about 90% the speed of light.
Repeat observations by the Chandra X-Ray Observatory over a decade have revealed a possible self-regulation mechanism for the growth rate of the black hole. The jet of ejected material is occasionally choked off by a hot wind blowing off the accretion disk, depriving the jet of needed material. When the wind dies down, the jet returns.
Reader's Guide
GRS 1915+105 holds a significant place in astrophysics as the first known galactic source to exhibit apparent superluminal motion in its jets, a phenomenon previously observed only in extragalactic sources. Its discovery in 1992 by the WATCH all-sky monitor aboard Granat opened a new window into the study of relativistic jets within the Milky Way. The system's microquasar nature, with a black hole of 10 to 18 solar masses rotating at extreme speeds (at least 950 times per second, spin parameter >0.82), provides a unique laboratory for testing theories of accretion and jet formation. High-resolution radio observations with VLA, MERLIN, and VLBI have confirmed that the apparent superluminal motion is a relativistic effect, with intrinsic jet velocities around 90% the speed of light. Additionally, decade-long Chandra X-ray Observatory observations have suggested a self-regulating growth mechanism, where a hot wind from the accretion disk periodically chokes off the jet, offering insights into how such systems evolve. This system remains a key object for understanding black hole accretion, jet physics, and the dynamics of binary systems.
Did You Know?
- It was the first known galactic source to eject material with apparent superluminal motion, observed in 1994.
- The black hole rotates at least 950 times per second, with a spin parameter greater than 0.82.
- The intrinsic velocity of the jet ejecta is about 90% the speed of light.
Frequently Asked Questions
What is GRS 1915+105?
It is an X-ray binary system in the constellation Aquila, also catalogued as V1487 Aquilae. The system pairs a normal main-sequence star with a black hole, and the steady flow of stellar material onto the black hole powers a relativistic jet, classifying it as a microquasar.
What makes GRS 1915+105 so unusual among variable stars?
Its jet was observed in 1994 moving at an apparent speed exceeding the speed of light, making it the first object within our own galaxy to display such superluminal motion. That finding confirmed the same jet physics seen in distant quasars operate on a far smaller scale inside the Milky Way.
How far away is GRS 1915+105 and how was it found?
The system sits roughly 11,000 parsecs from Earth, well beyond the solar neighborhood but still within the galactic disk. It was first detected on August 15, 1992, by the WATCH all-sky monitor aboard the Granat satellite.
What do we know about the black hole in GRS 1915+105?
Estimates place its mass between 10 and 18 solar masses, with a spin parameter greater than 0.82. The black hole rotates at a rate of at least 950 spins per second, making it one of the fastest-spinning stellar-mass black holes known.
Why do variable-star fans keep bringing up GRS 1915+105?
It was the first confirmed galactic source to eject matter at apparent superluminal velocities, bridging the gap between stellar-mass binaries and extragalactic quasars. Its 1992 discovery and the 1994 jet observation turned it into a landmark object in X-ray astronomy.
More in Variable Stars, Part 4 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced