M33 X-7

M33 X-7 is an eclipsing X-ray binary located in the Triangulum Galaxy (M33), approximately 2.64 million light-years from Earth. It contains a black hole and a massive, hot companion star. What makes M33 X-7 particularly significant is that it holds the record for the most massive stellar-mass black hole known in a binary system, estimated to be around 15.65 times the mass of the Sun.

The system is an eclipsing binary, meaning that from our perspective, the companion star periodically passes in front of (eclipses) the black hole, causing a dip in the observed X-ray emission. This eclipsing nature allows for precise measurements of the system's orbital parameters, including the masses of the components.

The companion star in M33 X-7 is an O-type supergiant, a massive and luminous star nearing the end of its life. Its strong stellar winds are thought to be feeding the black hole's accretion disk, resulting in the observed X-ray emission.

The study of M33 X-7 provides valuable insights into the formation and evolution of massive black holes in binary systems, and helps constrain models of stellar evolution and binary star interactions. The system's well-determined parameters make it a key object for understanding the upper mass limits of black holes formed from the collapse of massive stars.