GRS 1915+105
What is GRS 1915+105?
Black holes & quasars· Distance 28,000 ly. A miniature quasar inside our galaxy. In 1994 its jets showed the first apparently faster-than-light motion ever seen within the Milky Way, and its X-ray flickering on timescales of seconds has made it a laboratory for black-hole disk physics.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where GRS 1915+105 is in your sky right now: https://nowsky.org/solar/sky?sel=grs 1915 — location and time set automatically, no login.
Its place in the sky
A black hole, in the direction of Aquila.
Mass, distance, nature
| Mass | ~12 Suns |
|---|---|
| Distance | ~28,000 ly |
| Companion | K-type giant, 33.5-day orbit |
| Jet speed | >90% of light speed, apparently superluminal |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Discovery and name
A microquasar found in 1992 — the first superluminal jet motion seen inside our galaxy.
Frequently asked
- What is the mass of GRS 1915+105?
- ~12 Suns.
- How far is GRS 1915+105 from Earth?
- ~28,000 ly.
- How fast is GRS 1915+105 travelling?
- >90% of light speed, apparently superluminal.
- Where in the sky is GRS 1915+105?
- In the direction of Aquila.
- Where is GRS 1915+105 in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
A few times a second — spin measured from X-ray flicker
The X-rays of GRS 1915+105 flicker regularly, tens to hundreds of times a second. These "quasi-periodic oscillations" are read as the orbital period of material at the innermost edge of the accretion disk, pressed against the black hole, and the shorter the period the closer in the disk reaches. How far in a disk can reach is set by the black hole's spin, so the flicker gave GRS 1915 a spin close to the theoretical maximum.
The same conclusion came from the shape of the iron line in the X-ray spectrum, making this the specimen of a black hole spinning near its limit. When the region near the event horizon turns at close to light speed, its rotational energy can power the jets, and GRS 1915's superluminal jets are cited as the evidence. Since 2018 the system has been shrouded in thick gas with its X-rays greatly weakened, and whether an active phase of nearly thirty years is ending is being watched.
The black hole in depth
GRS 1915+105 is a black-hole binary about 28,000 light-years away in Aquila, buried deep in the galactic disk. Discovered as an X-ray source by Russia's Granat satellite in 1992, it pairs a black hole of roughly 12 solar masses with a K-type giant in a 33.5-day orbit. Gas streaming off the giant feeds a huge accretion disk, and the system has stayed X-ray bright for more than three decades, a rare persistent source.
Radio observations in 1994 showed blobs in its jets appearing to cross the sky faster than light. The effect is a geometric illusion produced by material moving toward us at more than 90 percent of light speed, something previously seen only in distant quasars, hence the name microquasar. Its X-ray output flickers in a dozen distinct patterns on timescales of seconds to minutes, interpreted as the inner disk repeatedly emptying and refilling.
Interstellar dust hides even the companion star at visible wavelengths, so it is studied in infrared, radio and X-rays. Select GRS 1915+105 in the Sky view to see its position in southern Aquila in the heart of the Milky Way, and remember on a summer night that such an object lies hidden in that glow.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.