The most massive black holes reside at the centres of galaxies. Of those where
there is enough data to estimate the mass, the most massive is almost certainly
in the giant elliptical galaxy M87, which belongs to the Virgo Cluster of
galaxies. Measurements made with the Hubble Space Telescope suggest a mass 3
billion times the
Sun for the supermassive black hole at the centre of M87.
Spectra taken with the Hubble Space Telescope show that the gas 60 light years
from the centre of M87 is rotating at 2 million kilometres (1.2 million miles)
per hour, and that its speed increases towards the centre. Only the gravity of
an immense mass would prevent gas spinning at this speed from flying apart.
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