Question: Hi Anna so if there is a black hole on the centre of each galaxy and well I heard that it sort of sucks things inside how are galaxies existing ??

Anna Scaife answered on 15 Nov 2014:

Hey Khrystillianna – there is a super-massive black hole at the centre of nearly every galaxy, including our own! When we say that black holes suck things in, we’re really talking about the gravitational pull that they exert on other objects. Black holes have lots of mass (in a very small volume) so they can exert large gravitational pulls, but just because objects feel a gravitational force towards a black hole doesn’t mean that they’ll get sucked in. If they’re moving fast enough they’ll just change direction a bit and swing past the black hole. Other objects might just fall into stable orbits and circle the black hole like the Earth circles the Sun, or the Moon circles the Earth.

However… if things get too close to a black hole then they will definitely get sucked in. There’s a certain distance from a black hole that we call an “event horizon” – if anything gets closer than that point then it’s a goner. Fortunately the event horizon is pretty close to a black hole, so most of the matter in our galaxy and other galaxies is outside the event horizon and just ends up orbiting the black hole rather than getting sucked in 🙂