Great Annihilator
1E1740.7-2942, or the Great Annihilator, is a Milky Way microquasar, located near the Galactic Center on the sky. It likely consists of a black hole and a companion star. It is one of the brightest X-ray sources in the region around the Galactic Center.
The object was first detected in soft X-rays by the Einstein Observatory and later detected in hard X-rays by the Soviet Granat space observatory. Followup observations by the SIGMA detector on board Granat showed that the object was a variable emitter of massive amounts of photon pairs at 511 keV, which usually indicates the annihilation of an electron-positron pair. This led to the nickname, "Great Annihilator." Early observations also showed a spectrum similar to that of the Cygnus X-l, a black hole with a stellar companion, which suggested that Great Annihilator was also a stellar mass black hole.
The object also has a radio source counterpart that emits jets approximately 1.5 pc long. These jets are probably synchrotron emission from positron-electron pairs streaming out at high velocities from the source of antimatter. Modeling of the observed precession of these jets gives an object distance of approximately 5 kpc. This means that while the object is likely located along our line of sight towards the center of the Milky Way, it may be closer to us than Sagittarius A*, the black hole at the center of our galaxy.
