LS 5039 system

A binary star system, the LS 5039 system comprises a compact object in an eccentric 3.9 day orbit around a massive blue giant star (spectral type O6.5V). The compact object is likely a black hole.

The two objects orbit each other at very short distance, varying between only 0.2 and 0.4 AUs, with one orbit completed every four standard days. As it dives towards the blue giant star, the compact companion is exposed to the strong stellar wind and the intense light radiated by the star, allowing on the one hand particles to be accelerated to high energies, but at the same time making it increasingly difficult for gamma rays produced by these particles to escape. The interplay of these two effects results in a strong regularly scheduled gamma ray signal, accurate as a clock.