Cosmic Scale
Holmberg 15A*
Ultramassive black hole · 700 million light-years
How big is Holmberg 15A*?
Holmberg 15A* is about 0.03 light-years across.
See Holmberg 15A* in 3D, at true scale
Holmberg 15A is the brightest galaxy of its cluster, and its centre is strangely empty of stars — the signature of a huge black hole that scattered them away during past galaxy mergers. Its mass, measured directly in 2019, is around 40 billion Suns.
At a glance
| Diameter | 0.03 light-years |
|---|---|
| Mass | 7.96 × 10⁴⁰ kg |
| Diameter compared with Earth | 1.9 × 10⁷ × Earth |
| Distance | 700 million light-years |
| Black hole | About 40 billion Suns |
| Core | Depleted of stars |
| Measured | 2019 |
Good to know
- It is the most massive black hole measured directly from the motions of stars, rather than estimated indirectly.
- Its starved core spans thousands of light-years — bigger than the Large Magellanic Cloud.
- The galaxy is thought to have formed from the collision of two already-large ellipticals.