Cram more than 100,000 stars into a cluster "only" 150 light-years wide and you get something like this - the globular cluster astronomers know as M-13. This image was assembled from Hubble data recorded during four separate observations from 1999 to 2006. It includes ultraviolet, visible and infrared portions of light spectrum.

M-13 is one of the brightest and best-known (to astronomers) globular clusters in the northern sky. If you're far enough from urban light pollution, it's even possible to spot this object with the naked eye, I'm told, only 25,000 light years away in the winter constellation Hercules. 

Folks at the Space Telescope Science Institute in Baltimore say the density of stars at the center of this cluster is about 100 times the density of stars in our sun's region of the Milky Way galaxy. Imagine the night sky on a planet circling one of those stars! The stars are so close together they sometimes smash into each other, creating new stars called "blue stragglers."

The red dots are older, giant stars. The bluish ones are young, hot stars.

Astronomers have counted almost 150 such clusters in a sort of halo that surrounds the Milky Way's spiral disk. They are believed to have formed before the spiral itself, and contain some of the oldest stars in the region.

Photo credits go to NASA, the European Space Agency and the Hubble Heritage Team at the space telescope institute.