• Question: hi my name is Nala and i want to know if you dont mind me asking but do you know how big the black hole is?

    Asked by boas534chon58 to stephaniebuttigieg, Ryan B, Eleonora S, conallkavanagh on 24 Mar 2026.
    • Photo: Conall Kavanagh

      Conall Kavanagh answered on 24 Mar 2026:

      This is a really good question and one to which there isnt exactly a straighforward answer. There have been lots of different attempts to try and ‘weigh’ black holes, including by studying what happens when they tear a star apart in a Tidal Disruption Event. We only know where black holes are by the way that material (gas and stars) near them behaves, and this is what we use to infer their mass. The supermassive black hole in the centre of our galaxy the Milky Way has been imaged with a disc of gas around it – we can study the light from this disc which gives us an estimate of the holes mass. Also stars have been imaged orbiting around the hole very rapidly and we can use their orbits again to put an estimate on the mass.

Comments

  • Photo: conallkavanagh

    conallkavanagh commented on :

    I should also add that we know that the mass of a galaxy and its central supermassive black hole are roughly related – heavier galaxies have heavier holes. Our supermassive black hole is called Sagitarius A* and weighs about 4 million times the mass of our sun (so about 8×10^36 kilograms). However, it is not uncommon to find ones which are heavier than a billion times the mass of our sun (so at least a thousand times heavier than ours)!