spacetoday.net: Hubble sees faintest stars in cluster

Posted: Fri, Aug 18, 2006, 8:13 AM ET (1213 GMT)
NGC 6397 (STScI)

Astronomers using the Hubble Space Telescope have detected the faintest stars ever found in a globular cluster, a discovery that helps refine the age of the cluster as well as the minimum mass needed for a star to exist. Hubble observations of NGC 6397, a globular cluster 8,500 light-years from the Earth, turned up white dwarfs so faint their light was equivalent to a birthday candle on the Moon as seen from the Earth. The discovery of those stars allowed astronomers to calculate the age of the cluster at approximately 12 billion years. The observations also appeared to confirm models of stellar formation that set a minimum mass on stars of about 80 Jupiter masses: even the dimmest stars seen in the Hubble images have masses greater than this limit.