Why do galaxies have black holes at the center?
Supermassive black holes at the centres of galaxies affect the evolution of the galaxy.
It is now thought that most large galaxies have a supermassive black hole at their centres. Our Milky Way galaxy has a black hole with a masses of some 4 million times that of the Sun at its centre at Sagittarius A*.
It has been observed that there is a relationship between the mass of the central supermassive black hole and the mass of the central bulge of the galaxy. Typically the mass of the central galactic bulge is some 700 times the mass of the supermassive black hole.
It has also been observer that there is a relationship between the orbit speed of outer stars of a galaxy and the mass of the supermassive black hole.
Some theories suggest that the supermassive black holes served as seeds around which galaxies formed.
Other observations suggest that emissions from the black hole affects the rate of star formation in the galaxy.
There is therefore growing evidence that supermassive black holes influence the evolution of galaxies. Galaxies without a supermassive black hole probably had one but lost it during a collision with another galaxy or black hole.