Cygnus X-1

black hole feeding on a blue supergiant · 21 Suns

7,300 light-years from Earth

The first object widely accepted as a black hole (1971). Every 5.6 days it circles a blue supergiant 40 times the Sun's mass, stripping gas into a disk hot enough to shine in X-rays. Stephen Hawking famously bet it was not a black hole, and lost.

• the two orbit 0.2 AU apart, half of Mercury's distance from the Sun
• X-rays come from gas at millions of degrees just before it falls in

kind

black hole

size

125 km across (event horizon)