Sirius, Rigel, Pollux and Castor
A galaxy!
There are 400 billion stars in our galaxy - we can't name them all.
constellation
No galaxy by that name exists.
The smallest galaxy - a dwarf galaxy - will contain stars upwards of 30 billion stars. You are thinking of an open cluster, which as the name suggests, is a cluster of stars, not a galaxy. An open cluster is a group of up to a few thousand stars.
A galaxy contains stars, gas and dust. In a spiral galaxy like the Milky Way, the stars, gas, and dust are organized into a "bulge," a "disk" containing "spiral arms," and a "halo." Elliptical galaxies have a bulge-like central region and a halo, but do not have a disk.
galaxy
If they form a galaxy, it's called a galaxy of course.
If the group is large enough, "galaxy" or "dwarf galaxy."
Milky Way Galaxy
Our Galaxy (the milky way)
All galaxies contain hot blue stars...