NGC 4889
What is NGC 4889?
Black holes & quasars· Distance 300 million ly. A giant black hole whose mass of about 21 billion Suns was measured from the motions of stars in 2011. It sits at the centre of the brightest galaxy in the Coma Cluster and is quiet today, swallowing little gas.
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Its place in the sky
A black hole, in the direction of Coma Berenices.
Mass, distance, nature
| Mass | ~21 billion Suns (from stellar motions) |
|---|---|
| Distance | ~300 million ly (Coma Cluster) |
| Event horizon | ~130 billion km, 14× Neptune's orbit |
| Apparent magnitude | 11.4 |
| How the mass is measured | modelling the speeds of stars in the galaxy’s centre |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Discovery and name
A giant elliptical in the Coma Cluster; its 21-billion-Sun black hole (2011) was then the record.
The wide error bars on NGC 4889's black hole
Close to a black hole, the motions of stars are governed more by the black hole's gravity than by the galaxy's as a whole. So measuring how fast stars move at each point near a galaxy's centre lets astronomers calculate the black hole's mass. But in a galaxy 300 million light-years away this region looks extremely small on the sky, barely large enough for big telescopes to split apart.
That is why the figure of 21 billion carries a large uncertainty: the study gave a range from 6 billion to 37 billion Suns. Because nobody knows exactly which way the stars' orbits lean, the result changes with the assumptions used. Even the lowest value, though, is more than a thousand times the mass of the black hole at the centre of our own galaxy.
The black hole in depth
NGC 4889 is the brightest giant elliptical galaxy in the Coma Cluster, about 300 million light-years away toward Coma Berenices. In 2011 a team used the Gemini and Keck telescopes in Hawaii to measure how fast the stars at its centre move, and calculated a central black hole of about 21 billion Suns. The same study found about 9.7 billion Suns for the black hole in another galaxy, NGC 3842.
At the time it was the heaviest black hole measured directly from the motions of stars. Its event horizon is about 130 billion km across, more than 14 times the width of Neptune's orbit. Scientists think it once swallowed gas eagerly and shone brightly as a quasar long ago. Today it has little gas left to swallow and is quiet.
The galaxy itself is about 11th magnitude, so on a clear spring night a 20-cm telescope shows it and its neighbour NGC 4874 as two smudges at the heart of the cluster. In the Sky view it appears in Coma Berenices, east of Denebola, the star at the Lion's tail, close to overhead on spring evenings. Together the two galaxies mark the centre of a cluster of more than a thousand galaxies.
Frequently asked
- What is the mass of NGC 4889?
- The mass of NGC 4889 is ~21 billion Suns (from stellar motions).
- How far is NGC 4889 from Earth?
- The distance of NGC 4889 is ~300 million ly (Coma Cluster).
- How bright is NGC 4889 (apparent magnitude)?
- The apparent magnitude of NGC 4889 is 11.4.
- Where in the sky is NGC 4889?
- NGC 4889 lies in the direction of Coma Berenices.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.