Question: I saw a program about space (mabye Panorama) that said the center of spiral galxies like the milky way are Super black holes. My questions are, is this true? Whats the diference between a black hole and a super black hole? and how are they formed?

Charlie Ryan answered on 20 Mar 2011:

hi frogdwarf! ok i don’t really know the answer to this question – sorry! I know that black holes are formed when very, very large stars run out of fuel, the nuclear fusion stops and the star collapses in a supernova explosion. The force of gravity pulls the mass into an infinitessally small point. I’ve also heard that there supermassive black holes in the centre of galaxies – they have been spotted by the way the surrounding stars orbit around them (you can’t see them too well directly!). (black holes do emit a tiny bit of radiation (called Hawking radiation) but this is very hard to spot).
I’ve had to look up supermassive black holes – i’m no strophysicist! There seems to be various ways that they form, with the most obvious being that they are bloated normal black holes, that have eaten a lot of matter. There are some other diferences between them and other black holes – they don’t seem very dense (weird – i don’t understand this!).
It seems that most galaxies do have supermassive black holes at their centre – but no one seems sure why! No one knows whether the super massive black hole was there first and seeded the formation of the galaxy, or the other way round.
Thanks for your question – you’ve managed to get me interested in this!