V404 Cygni is a microquasar and a binary system consisting of a black hole with a mass of about 12±3 solar masses and a late G or early K companion star of mass slightly smaller than the Sun in the constellation of Cygnus. The star and the black hole orbit each other every 6.47129 d at fairly close range. Due to their proximity the main sequence star would be distorted into egg shape by the black hole's gravity and lose mass to the black hole.The "V" in the name indicates that it is a variable star, which repeatedly gets brighter and fainter over time. It is also considered a nova, because at least three times in the 20th century it produced a bright outburst of energy. Finally, it is a soft X-ray transient because it periodically emits short bursts of X-rays.