GALACTIC BLACK HOLES

Most of the galaxies are thought to have a black hole at its center-collapsed stars with such a strong gravitational field that even light cannot escape from them, which is why they cannot be seen directly.Galaxies have large black holes that pull in a constant stream of dust and star fragments.There is probably a relatively small black hole just 100000 times the mass of the sun - at the center of our galaxy.Scientists are able to detect black holes because their colossal gravity draws in surrounding matter which, as it descends into black hole becomes very hot and begins to glow , thereby revealing  the black holes' position.