A swarm of ancient stars
Studying these stellar swarms has revealed much about the history of our galaxy and how stars evolve.
December 9, 2010
We know of about 150 of the rich collections of old stars called globular clusters that orbit our galaxy, the Milky Way. This sharp new image of M107, captured by the Wide Field Imager on the 2.2-meter telescope at the European Southern Observatory’s (ESO) La Silla Observatory in Chile, displays the structure of one such globular cluster in exquisite detail. Studying these stellar swarms has revealed much about the history of our galaxy and how stars evolve.
The globular star cluster M107.
Photo by ESO/ESO Imaging Survey
The globular cluster M107 (NGC 6171) is a compact and ancient family of stars that lies about 21,000 light-years away. M107 is a bustling metropolis: Thousands of stars in globular clusters like this one are concentrated into a space that is only about 20 times across the distance between our Sun and its nearest stellar neighbor, Alpha Centauri. A significant number of these stars have already evolved into red giants, one of the last stages of a star's life, and have a yellowish color in this image.
Globular clusters are among the oldest objects in the universe. And since the stars within a globular cluster formed from the same cloud of interstellar matter at roughly the same time — typically more than 10 billion years ago — they are all low-mass stars, as lightweights burn their hydrogen fuel supply more slowly than stellar behemoths. Globular clusters formed during the earliest stages in the formation of their host galaxies, and therefore studying these objects can give significant insights into how galaxies and their component stars evolve.
M107 has undergone intensive observations, being one of the 160 stellar fields that was selected for the Pre-FLAMES Survey – a preliminary survey conducted between 1999 and 2002 using the 2.2-meter telescope at ESO to find suitable stars for follow-up observations with the Very Large Telescope’s (VLT) spectroscopic instrument FLAMES. Using FLAMES, it is possible to observe up to 130 targets at the same time, making it particularly well suited to the spectroscopic study of densely populated stellar fields, such as globular clusters.
M107 is not visible to the naked eye, but, with an apparent magnitude of about 8, it can easily be observed from a dark site with binoculars or a small telescope. The globular cluster is about 13 arcminutes across, which corresponds to about 80 light-years at its distance, and it is found in the constellation Ophiuchus, north of the pincers of Scorpius. Roughly half of the Milky Way's known globular clusters are actually found in the constellations Sagittarius, Scorpius, and Ophiuchus, in the general direction of the center of the Milky Way. This is because they are all in elongated orbits around the central region and are on average most likely to be seen in this direction.
M107 was discovered by Pierre Mechain April 1782, and it was added to the list of seven additional Messier Objects that were originally not included in the final version of Messier's catalog, which was published the previous year. On May 12, 1793, William Herschel, who was able to resolve this globular cluster into stars for the first time, independently rediscovered it. But it was not until 1947 that this globular cluster finally took its place in Messier's catalog as M107, making it the most recent star cluster to be added to this famous list.
This image is composed from exposures taken through the blue, green and near-infrared filters by the Wide Field Camera (WFI) on the MPG/ESO 2.2-meter telescope at the La Silla Observatory.