NGC 1277


The biggest black hole whose mass has so far been properly measured lies at the heart of a galaxy called NGC 1277, 250 million light years from Earth in the constellation of Perseus – and it’s a real whopper. While our own galaxy’s central black hole has an estimated mass of 4.1 million Suns, the black hole in NGC 1277 is around 17 billion solar masses.

Astronomers discover and assess black holes in distant galaxies by measuring the orbits of the stars that surround them. Many have now been found, with masses equivalent to millions or even billions of Suns, but they usually follow a fairly strict relationship that limits the black hole to around 0.1 per cent of the host galaxy’s mass – the more massive the galaxy, the bigger the black hole. In 2012, however, a team led by Remco van den Bosch of Germany’s Max Planck Institute for Astronomy announced their discovery of ‘supergiant’ black holes in relatively small galaxies. NGC 1277 is the most impressive of these: the galaxy itself contains a lot less material than our Milky Way, with an overall mass of 120 billion Suns, so its central black hole accounts for a staggering 14 per cent of all its mass. At this order of magnitude, it’s probably about four light days across – roughly 11 times the diameter of Neptune’s orbit around the Sun.

As yet, astronomers are still struggling to come up with a workable theory to explain these supergiant black holes. However, NGC 1277 may not hold its record as the biggest black hole of all for long. The much larger giant elliptical galaxy NGC 4889 contains a black hole with a mass of between 6 billion and 37 billion solar masses, and astronomers will probably find a way to lock down its mass with more accuracy soon.

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