There is an article in Discover magazine, June 1990, page 68 about this object. Also called 1E1740.7-2942 or the 'microquasar', it is an unresolved 'point source' that emits a variable flux of 511 keV X-ray radiation which is the signature of the annihilation of electrons and their anti-matter partners. However, this radiation comes out at an energy of 170 keV due to a proposed 'Compton backscattering' process in the object. This radiation was detected twice by balloon-borne instruments in 1978 and 1993 from a region within 15 degrees of the Galactic center, but the Compton Gamma Ray Observatory has not been able to confirm the existence of this source in a study by D. Smith, M. Leventhal and their colleagues, published in the Astrophysical Journal.
Previously, it was proposed that this is a small black hole, and the radiation occurs on the inner edge of an accreting disk of gas. The 'backscatter' feature is seen from the far-side of the disk and represents the annihilation of some 10^44 electrons per second. I think the jury is still out on exactly what this object is.
Here is another short comment about it from Physics Today:
THE GREAT ANNIHILATOR MAY BE A MICROQUASAR . The object 1E1740.7-2942 near the center of the Milky Way is an x-ray emitter and also the brightest source of positrons in the sky; the positrons reveal themselves through their collisions with electrons, resulting in the characteristic gamma radiation at 511 keV and hence the name Great Annihilator. A team of French astronomers, using the Very Large Array in New Mexico, has now studied the object at radio wavelengths and found that it exhibits radio-emitting jets whose behavior is synchronous with the variable gamma source. All of this suggests to the French astronomers that the core of 1E1740.7-2942 resembles a sort of mini-quasar. (Nature, 16 July 1992.)
Copyright 1997 Dr. Sten Odenwald
Return to Ask the Astronomer.