An Old Star Cluster

An ancient globuleThis is NGC 6535, a globular cluster 22,000 light-years away in the constellation of Serpens (The Serpent). It’s about one light-year across.

Globular clusters are tightly bound groups of stars which orbit galaxies. The Latin word globulus, from which these clusters take their name, means a small sphere.  A large mass in the rich stellar centre of a globular cluster pulls the stars inward to form a ball of stars.

Globular clusters are generally very ancient objects that form around the same time as their host galaxy. Thus far, no new star formation has been observed within amy globular cluster. The lack of young stars explains the abundance of aging yellow stars in this image, most of them containing very few heavy elements.

Image Credit: NASA

A Stellar Nursery

LH_95These swirls of gas and dust and the stars clustered in and around them are know as LH 95. It a region of low-mass, infant stars and their much more massive stellar neighbors found in the Large Magellanic Cloud.

The largest stars in LH 95 (those with at least 3X the mass of the Sun) generate strong stellar winds and high levels of UV radiation that heat the surrounding interstellar gas. The result is a bluish nebula of glowing hydrogen expanding outward into the molecular cloud that originally collapsed to form these massive stars. However, some dense parts of this star-forming region remain intact despite the stellar winds. The appear as dark dusty filaments in the picture. These dust lanes absorb some of the blue light emitted by the stars behind them causing them appear redder. Other parts of the molecular cloud have contracted to form infant stars, the fainter of which have a high tendency to cluster.

Image Credit: NASA

A Massive Star Cluster

hs-1999-30-b-full_jpgThis star cluster lurks less than 100 light-years from the very center of our galaxy. With an equivalent mass greater than 10,000 stars like our Sun, the monster cluster is 10 times larger than a typical young star clusters found in the Milky Way. This cluster is destined to be ripped apart in just a few million years by gravitational tidal forces in the galaxy’s core, but during its brief lifespan, it will shine more brightly than almost every other star cluster in the galaxy.

Image Credit: NASA