European Southern Observatory | VLT | 2014 Sep 10
VLT observations of Messier 54 show the lithium problem also applies outside our galaxy This new image from the VLT Survey Telescope at ESO’s Paranal Observatory in northern Chile shows a vast collection of stars, the globular cluster Messier 54. This cluster looks very similar to many others but it has a secret. Messier 54 doesn’t belong to the Milky Way, but is part of a small satellite galaxy, the Sagittarius Dwarf Galaxy. This unusual parentage has now allowed astronomers to use the Very Large Telescope (VLT) to test whether there are also unexpectedly low levels of the element lithium in stars outside the Milky Way.
The Milky Way galaxy is orbited by more than 150 globular star clusters, which are balls of hundreds of thousands of old stars dating back to the formation of the galaxy. One of these, along with several others in the constellation of Sagittarius (The Archer), was found in the late eighteenth century by the French comet hunter Charles Messier and given the designation Messier 54.
For more than two hundred years after its discovery Messier 54 was thought to be similar to the other Milky Way globulars. But in 1994 it was discovered that it was actually associated with a separate galaxy — the Sagittarius Dwarf Galaxy. It was found to be at a distance of around 90 000 light-years — more than three times as far from Earth as the galactic centre.
Astronomers have now observed Messier 54 using the VLT as a test case to try to solve one of the mysteries of modern astronomy — the lithium problem. ...
The cosmological Lithium problem outside the Galaxy: the Sagittarius globular cluster M54 - A. Mucciarelli et al
- Monthly Notices of the RAS 444(2) 1812 (2014 Oct 21) DOI: 10.1093/mnras/stu1522
arXiv.org > astro-ph > arXiv:1407.7596 > 28 Jul 2014
See also: http://asterisk.apod.com/viewtopic.php?t=33835