How We Know Cygnus X1 is a Black Hole

This is another short bit from an upcoming drop!

• Observational Evidence for Black Holes: Cygnus X-1, a bright X-ray source, is considered the first astronomical object widely accepted as a black hole.
• Cygnus X-1 Characteristics: A binary system with an O9 supergiant star orbiting a black hole, located approximately 2220 parsecs away.
• System Properties: The system has a 5.6-day orbital period and a nearly circular orbit of 0.2 astronomical units.
• Black Hole Mass: The black hole in Cygnus X-1 has a mass between 14 and 21 solar masses, with the higher estimate being the current consensus.
• Accretion Disk Size: The accretion disk around the black hole is relatively small, with a diameter of approximately 15,000 km.
• Event Horizon Size: The event horizon of the black hole is smaller than 300 km, based on the rapid X-ray bursts observed.
• Black Hole Formation: The black hole likely formed from a massive star (greater than 40 solar masses) that either underwent a supernova or a direct collapse.
• Companion Star’s Characteristics: The companion star’s elevated helium content suggests it accumulated material from the black hole’s progenitor star.
• Significance of Cygnus X-1: Cygnus X-1 is a well-known example of a stellar-mass black hole, representing a relatively small population of known objects in this mass range.