system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a massive piece of mass at the center of galaxies?

In solar systems like our own, planets revolve around the sun. So, is there an object that galaxies gravitate towards and revolve around?
gpt
Yes, many galaxies have a supermassive black hole at their center, including ours (it's over two million times the massive the sun and about the radius of Neptune's orbit). However, it only makes up a small fraction of the mass of a galaxy, compared to a star which is by far the dominant source of mass in a solar system.