For 10 points, give this term for star systems like the Andromeda and our Milky Way.
The "Antennae" are two of these objects that are colliding with each other. These systems have velocities measurable by Doppler shift that are proportional to their distance from Earth, according to Hubble's law. Sagittarius A* ["A-star"] is a supermassive (*) black hole at the center of the one of these systems nearest to Earth. These systems can be irregular, spiral, or elliptical. For 10 points, give this term for star systems like the Andromeda and our Milky Way.
The "Antennae" are two of these objects that are colliding with each other.
galaxy