Black hole
LMC X-3
A slowly spinning black hole paired with a B star in the LMC
A black hole in the north of the Large Magellanic Cloud fed by a B star overflowing its Roche lobe. Its disc is remarkably stable compared with its Milky Way counterparts; one of the first objects to have its black-hole spin measured (a* ≈ 0.25).
| Mass | 6.98 solar masses |
|---|---|
| Event horizon radius | 21 km: the size of a city |
| Time for light to circle the event horizon once | 4.3 × 10⁻⁴ seconds |
| Mass | 6,98 M☉ |
| Companion | B3 V, ~3,6 M☉ |
| Orbital period | 1.70 days |
| Distance | 48 kpc (LMC) |
| Discovery | 1971 (Uhuru) |
The event horizon is the boundary where the escape velocity equals the speed of light: nothing inside, not even light, can get out. Its radius grows in direct proportion to the mass (the Schwarzschild radius, for a non-rotating black hole).