April 8, 2013
NGC 2100, an open cluster in the LMC
Image Credit: ESO/David Roma
NGC 2100 is an open cluster of around 15 million years old, located some 163,000 light-years away within the Large Magellanic Cloud, a small satellite galaxy of the Milky Way, in the constellation of Dorado, the Swordfish. The cluster is surrounded by glowing gas from the nearby Tarantula Nebula (30 Doradus).
Star clusters are groups of stars that formed around the same time from a single cloud of gas and dust. The stars with the most mass tend to form in the center of the cluster, while those with less mass dominate the outer regions. This, along with the greater number of stars concentrated in the center, makes the middle of the cluster brighter than the outer regions.
NGC 2100 is an open cluster, which means its stars are relatively loosely bound by their mutual gravity. These clusters have a lifespan measured in tens or hundreds of millions of years. They then drift apart over time under the effect of gravitational perturbations from other objects and eventually disperse entirely with each individual star travelling on its own way through the cosmos.
Globular clusters, which look similar to the untrained eye, contain many more older stars and are much more tightly bound, and so have far longer lifespans: many globular clusters have been measured to be almost as old as the Universe itself. So while NGC 2100 might be older than its neighbors in the Large Magellanic Cloud, it is still a youngster by the standards of star clusters. Because it’s shape is approximately round, NGC 2100 is sometimes mistaken as a globular cluster.
However, the glowing gas of the Tarantula Nebula tries to steal the limelight in this image — the bright colors here are the nebula’s outskirts. The blue regions show the presence of ionized oxygen. The energy required to ionize the oxygen is supplied by the massive stars located deeper within the Tarantula Nebula, specifically within the super star cluster RMC 136.
The red glow at the base of the image displays the presence of less energetic excited hydrogen marking the edge of the influence of the monster stars within RMC 136 and where smaller, cooler and less energetic stars dominate. The stars that make up NGC 2100 are older and less energetic, and hence have little or no nebulosity associated with them.
The smaller star cluster, close to the right-hand edge of the picture and just below center, is the open cluster NGC 2092.
This image was created from exposures through several different color filters using the EMMI instrument on the New Technology Telescope at ESO’s La Silla Observatory in Chile. The stars are shown in their natural colors, while light from glowing ionized hydrogen (red) and oxygen (blue) is overlaid. The colors that appear in nebulae depend on the temperatures of the stars lighting them up.
Data for this image were selected from ESO’s data archives by Hidden Treasures entrant David Roma as part of the astrophotography competition held by ESO in 2010.