Hubble Sees a Vast "City" of Stars
In these pictures, a "city" of a million stars glitters like a New York City skyline. The images capture the globular cluster 47 Tucanae, located 15,000 light-years from Earth in the southern constellation Tucana.
Using NASA's Hubble Space Telescope, astronomers went hunting in this large city for planetary companions: bloated gaseous planets that snuggle close to their parent stars, completing an orbit in a quick three to five days. To their surprise, they found none. This finding suggests that the cluster's environment is too hostile for breeding planets or that it lacks the necessary elements for making them.
The picture at left, taken by a terrestrial telescope, shows most of the cluster, a tightly packed group of middle-aged stars held together by mutual gravitational attraction. The box near the center represents the Hubble telescope's view.
The image at right shows the Hubble telescope's close-up look at a swarm of 35,000 stars near the cluster's central region. The stars are tightly packed together: They're much closer together than our Sun and its closest stars. The picture, taken by the Wide Field and Planetary Camera 2, depicts the stars' natural colors and tells scientists about their composition and age. For example, the red stars denote bright red giants nearing the end of their lives; the more common yellow stars are similar to our middle-aged Sun. Most of the stars in the cluster are believed to have formed about 10 billion years ago. The bright, blue stars - thought to be remnants of stellar collisions and mergers - provide a few rejuvenated, energetic stars in an otherwise old system. The Hubble picture was taken in July 1999.
Hubble image: NASA and Ron Gilliland (Space Telescope Science Institute);
Ground-based image: David Malin, © Anglo-Australian Observatory