Supermassive black h oles outside the Milky Way It is now widely accepted that the center of nearly every galaxy contains a supermassive black hole.   The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M-sigma relation ,  strongly suggests a connection between the formation of the black hole and the galaxy itself.  . The explanation for this correlation remains an unsolved problem in astrophysics. It is believed that black holes and their host galaxies coevolved between 300-800 million years after the Big Bang , passing through a quasar phase and developing correlated characteristics, but models differ on the causality of whether black holes triggered galaxy formation or vice versa, and sequential formation cannot be excluded. The unknown nature of dark matter is a crucial variable in these models. 
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