• Question: What is it that causes the galaxies to stay together? why don't they just float apart?

    Asked by cai192546 to Kimberley, Sara on 20 Jun 2011.
    • Photo: Sara Imari Walker

      Sara Imari Walker answered on 20 Jun 2011:

      Hi cai! Galaxies stay together for the same reason we are stuck to the ground here on Earth. Gravity!! Gravity is interesting because it is strongest on large scales, where there is a lot of mass! Galaxies are huge, full of billions stars. These stars are held together in the galaxy by their mutual gravitational attraction. There also happens to be a supermassive black hole (a strong source of gravity) at the center of each galaxy. They helps keep it all together. Pretty crazy – baseballs and galaxies obey the same physics!