Conversation so far:
what celestial object lies at the center of the milky way galaxy
The Galactic Center is the rotational center of the Milky Way, a supermassive black hole which powers the compact radio source Sagittarius A-Star.
how much mass is contained in a supermassive black hole
A supermassive black hole contains a mass of the order of hundreds of thousands to billions of times the mass of the Sun.

Question: do all galaxies have one
Self-contained rewrite: do all galaxies have a supermassive black hole