Phoenix A
What is Phoenix A?
Black holes & quasars· Distance 5.7 billion ly. A black hole in the central galaxy of the Phoenix Cluster, about 5.7 billion light-years from Earth, toward the constellation Phoenix. An indirect calculation puts its mass near 100 billion Suns, making it one of the heaviest black-hole candidates known.
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Its place in the sky
A black hole, in the direction of Phoenix.
Mass, distance, nature
| Mass | ~100 billion Suns (indirect estimate) |
|---|---|
| Distance | ~5.7 billion ly (z = 0.6) |
| Host | central galaxy of the Phoenix Cluster |
| Star formation | ~740 solar masses per year |
| How the mass is measured | an indirect estimate from scaling relations with the host galaxy — not a direct measurement |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Discovery and name
Center of the Phoenix Cluster (2012); its black hole may reach 100 billion Suns, near the theoretical limit.
The Phoenix Cluster, found by its shadow
The Phoenix Cluster was found not by its light but by its shadow. Faint microwaves left over from the Big Bang, the cosmic background radiation, arrive from every direction. The hot gas inside a cluster scatters these microwaves, so at certain wavelengths the cluster's patch of sky looks slightly darker than its surroundings. This is called the Sunyaev–Zeldovich effect.
The South Pole Telescope swept across a large area of the southern sky looking for such shadows and found the Phoenix Cluster in 2010. Because the shadow hardly weakens with distance, the method is well suited to finding massive clusters far across the universe. X-ray and visible-light follow-up then showed that the cluster is one of the most massive known and that stars are forming unusually fast at its centre.
The black hole in depth
The Phoenix Cluster is a huge gathering of galaxies about 5.7 billion light-years away toward the constellation Phoenix. The space between its galaxies is filled with gas at tens of millions of degrees that shines in X-rays. Its central galaxy makes new stars at a rate of about 740 Suns a year, compared with roughly one Sun a year in the Milky Way.
In most clusters the giant central black hole pours out energy that keeps the gas hot, so the gas has trouble cooling into stars. In the Phoenix Cluster this brake is unusually weak, so many stars form. The mass of its central black hole, Phoenix A, was not measured from the motions of stars. It was calculated with a model based on how stars are packed in the central galaxy and on the behaviour of the cluster's gas, and the answer is about 100 billion Suns.
That calculation is very uncertain. If it is right, the event horizon would be about 600 billion km across, a distance light would take about 23 days to cross. The cluster is far too faint for amateur telescopes. In the Sky view it appears within Phoenix, a constellation that rises only low in the south on autumn evenings from places such as New York, never clears the horizon from London, and is best seen from the Southern Hemisphere.
Frequently asked
- What is the mass of Phoenix A?
- The mass of Phoenix A is ~100 billion Suns (indirect estimate).
- How far is Phoenix A from Earth?
- The distance of Phoenix A is ~5.7 billion ly (z = 0.6).
- Where in the sky is Phoenix A?
- Phoenix A lies in the direction of Phoenix.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.