Credit: ESA/Hubble & NASA
Shown here in a new image taken with the Advanced Camera for Surveys (ACS) on board the NASA/ESA Hubble Space Telescope, is the globular cluster NGC 1783. This is one of the biggest globular clusters in the Large Magellanic Cloud, a satellite galaxy of our own galaxy, the Milky Way, in the southern hemisphere constellation of Dorado.
First observed by John Herschel in 1835, NGC 1783 is nearly 160 000 light-years from Earth, and has a mass around 170 000 times that of the Sun.
Globular
clusters are dense collections of stars held together by their own
gravity, which orbit around galaxies like satellites. The image clearly
shows the symmetrical shape of NGC 1783 and the concentration of stars
towards the centre, both typical features of globular clusters.
By
measuring the colour and brightness of individual stars, astronomers
can deduce an overall age for a cluster and a picture of its star
formation history. NGC 1783 is thought to be under one and a half
billion years old — which is very young for globular clusters, which are
typically several billion years old. During that time, it is thought to
have undergone at least two periods of star formation, separated by 50 to 100 million years.
This
ebb and flow of star-forming activity is an indicator of how much gas
is available for star formation at any one time. When the most massive
stars created in the first burst of formation explode as supernovae they
blow away the gas needed to form further stars, but the gas reservoir
can later be replenished by less massive stars which last longer and
shed their gas less violently. After this gas flows to the dense central
regions of the star cluster, a second phase of star formation can take
place and once again the short-lived massive stars blow away any
leftover gas. This cycle can continue a few times, at which time the
remaining gas reservoir is thought to be too small to form any new
stars.
A version of this image was entered into the Hubble's Hidden Treasures image processing competition by contestant Judy Schmidt.
