Astronomers have spotted an enormous black hole – the second most massive ever – but it resides in a tiny galaxy.
The galaxy NGC 1277, just a quarter the size of our own Milky Way, hosts a black hole 4,000 times larger than the one at the Milky Way‘s centre.
The surprise finding is hard to reconcile with existing models of black hole growth, which hold that they evolve in tandem with host galaxies.
Getting to grips with just how large black holes are is a tricky business – after all, since they swallow light in their vicinities, they cannot be seen.
In the Milky Way, it is possible to observe individual stars as they orbit Sagittarius A, our own local black hole, to guess its mass.
But for the 100 or so far more distant black holes whose masses have been estimated, astronomers have made average measurements of associated stars’ speeds – their “velocity dispersion”.
On a hunt for the Universe’s largest black holes, astronomers using the Hobby-Eberly Telescope in the US state of Texas undertook a survey that brought in a haul of nearly 900 host galaxies.
But Remco van den Bosch, then at the University of Texas at Austin, and his colleagues were surprised to find that some of the largest black holes were to be found in small galaxies.
Among them was NGC 1
“We make a model of the galaxy and compute all the possible stellar orbits,” Dr Van den Bosch, who is now at the Max Planck Institute for Astronomy in Germany, explained to BBC News.277, 220 million light years away in the constellation Perseus, which happens to appear also in a high-resolution Hubble Space Telescope image, helping the researchers to refine their computer models.
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