You cannot PROVE that there are black holes in the cores of EVERY galaxy, but the ones that are close by, or show nuclear activity seem to also show signs that there are supermassive black holes living inside them. Since 1994 we have crossed an important threshold in black hole research. The Hubble Space Telescope has let astronomers peer closely at the cores of many galaxies and we see the unmistakable signs of massive black holes whipping the gas and stars into a frenzy. Supermassive black holes are no longer considered to be hypothetical, but are now part of the 'known' phenomena of astronomy. The debate over their existence has pretty much ended in the minds of most astronomers.
Thanks to the Hubble Space Telescope, the list gets longer every year. We do not expect that dwarf galaxies much smaller than the Milky Way will have black holes. It seems that the galaxy has to be large enough to have a rather well developed nuclear region with lots of stars crowded together in a small volume, for supermassive black holes to be a possibility.
Copyright 1997 Dr. Sten Odenwald
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