Cygnus X-1

Stellar-mass black hole

The first object widely accepted as a black hole, and the subject of a famous bet between Stephen Hawking and Kip Thorne. It pulls gas from a blue-supergiant companion.

Cygnus X-1, a stellar-mass black holeComputed render
Computed render: general-relativistic ray-trace; colours mapped to a visible range. Not a photograph.
21.2 ☉
mass (the Sun = 1)
63 km
event-horizon radius (computed)
7,200 ly
from Earth

Mass is a best estimate from the cited observations, which carry their own measurement uncertainty.

Its event horizon, the edge past which nothing returns, spans about 63 km in radius.

It lives in
Milky Way
Barred spiral galaxy.
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Black holes of similar mass
GW240530_012417Gravitational-wave source21.6 ☉GW190720_000836Gravitational-wave source20.8 ☉GW151226Gravitational-wave source20.7 ☉GW250119_190238Gravitational-wave source20.6 ☉GW240526_093944Gravitational-wave source22.1 ☉GW240825_055146Gravitational-wave source20.3 ☉
Worlds in the same direction on the sky→
Source: Curated from public catalogs via Wikidata (CC0). See data & analysis for full sourcing.
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