Globular Clusters are areas of space containing a large number of stars.

This stellar swarm is M80, one of the densest of the 147 known globular star clusters in the Milky Way galaxy. Located about 28,000 light years from Earth, M80 contains hundreds of thousands of stars, all held together by their mutual gravitational attraction. Globualr clusters are particularly useful for studying stellar evolution, since all of the stars in the cluster have the same age (about 15 billion years), but cover a range of stellar masses. Every star visible in this image is either more highly evolved than, or in a few rare cases more massive than, our own sun. Especially obvious are the bright red giants, which are stars similar to the Sun in mass that are nearing the ends of their lives.

M80 is also unusual because it was the site of a nova explosion in the year 1860. Nova outbursts occur when a close companion star transfers fresh hydrogen fuel to a burned-out white dwarf. Eventually the hydrogen ignites a thermonuclear explosion on the surface of the white dwarf, giving rise to the nova outburst. The ultraviolet Hubble observations have revealed the hot, faint remnant of this exploding star, which was named T Scorpii in the 19th century.

Astronomers using the recently installed infrared camera on NASA's Hubble Space Telescope have identified one of the most massive stars known, emitting as much as 10 million times the power of the Sun and with a radius larger than the distance between our Sun and the Earth. The star appears to be expelling its outer layers in violent eruptions, producing a brilliant nebula which now surrounds it.

The Pistol Star may have started with as much as 200 solar masses of material, but it is currently shedding much of its mass in violent eruptions. In the most recent eruptions, it might have expelled 10 solar masses of material.

Burning at such a rate, the star is destined to a short life and an abrupt end. It is currently one to three million years old and could die in a spectacular supernova at any time in the next three million years.