Dear all, i'm very new to cosmology/astronomy branches of physics. i've one simple question. it's known that the universe is expanding and i suppose the measurement was made by hubble for which he won the nobel prize. but also, i recently learnt that there're blackholes at the centre of galaxies like milky way. if that's true, the blackholes shud be 'sucking' in the other celestial bodies, wont they? in this case, considering there are many blackholes spread across the universe, isnt it cotradictory to the fact of 'expanding universe' ? could someone explain? thanks.