Outside the Milky Way: Globular cluster Messier 54

This new image from the ESO VLT Survey Telescope in northern Chile shows a vast collection of stars, the globular cluster Messier 54. 

This cluster looks similar to many others but it has a secret.

Messier 54 doesn't belong to the Milky Way, but is part of a satellite galaxy, the Sagittarius Dwarf Galaxy.

This parentage allowed astronomers to test whether there are also 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.

Most of the light chemical element lithium now present in the Universe was produced during the Big Bang, along with hydrogen and helium, but in much smaller quantities.

Astronomers can calculate quite accurately how much lithium they expect to find in the early Universe, and from this work out how much they should see in old stars, but the numbers don't match, there is about three times less lithium in stars than expected.

This mystery remains, despite several decades of work.

Up to now it has only been possible to measure lithium in stars in the Milky Way, but now a team of astronomers led by Alessio Mucciarelli (University of Bologna, Italy) has used the VLT to measure how much lithium there is in a selection of stars in Messier 54.

They find that the levels are close to those in the Milky Way. So, whatever it is that got rid of the lithium seems not to be specific to the Milky Way.

This new image of the cluster was created from data taken with the ESO VLT Survey Telescope (VST) at the Paranal Observatory.

As well as showing the cluster itself it reveals the extraordinarily dense forest of much closer Milky Way stars that lie in the foreground.

More information: This research was presented in a paper, "The cosmological Lithium problem outside the Galaxy: the Sagittarius globular cluster M54", by A. Mucciarelli et al., to appear in Monthly Notices of the Royal Astronomical Society (Oxford University Press). (PDF)

ESO VLT Survey Telescope (VST): Preview of treasure trove

The VLT Survey Telescope (VST) at ESO's Paranal Observatory in Chile has captured this richly detailed new image of the Lagoon Nebula. 

This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. 

This image is a tiny part of just one of eleven public surveys of the sky now in progress using ESO telescopes. 

Together these are providing a vast legacy of publicly available data for the global astronomical community. 

Credit: ESO/VPHAS+ team

The VLT Survey Telescope (VST) at ESO's Paranal Observatory in Chile has captured this richly detailed new image of the Lagoon Nebula.

This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters.

This image is a tiny part of just one of eleven public surveys of the sky now in progress using ESO telescopes.

Together these are providing a vast legacy of publicly available data for the global astronomical community.

The Lagoon Nebula is an intriguing object located around 5000 light-years from us in the constellation of Sagittarius (The Archer).

Also known as Messier 8, it is a giant cloud 100 light-years across, where new stars are forming within its plumes of gas and dust.


This new 17,000-pixel-wide image is from the VLT Survey Telescope (VST), one of two dedicated survey telescopes at ESO's Paranal Observatory in northern Chile.

A zoomable version of the image allows the viewers to explore the many nooks and crannies of this fascinating object.

The VST was not pointed at the Lagoon deliberately, it simply was included as part of a huge imaging survey called VPHAS+ that covered a much larger region of the Milky Way.

VPHAS+ is just one of three imaging surveys using visible light with the VST. These are complemented by six infrared surveys with the VISTA survey telescope.

The surveys are addressing many important questions in modern astronomy.

These include the nature of dark energy, searching for brilliant quasars in the early Universe, probing the structure of the Milky Way and looking for unusual and hidden objects, studying the neighbouring Magellanic Clouds in great detail, and many other topics.

History shows that surveys often find things that are unexpected and these surprises are crucial for the progress of astronomical research.

As well as the nine imaging surveys with VISTA and the VST there are also two additional surveys that are in progress using other ESO telescopes.

One, the Gaia-ESO Survey, is using the Very Large Telescope at Paranal to map the properties of more than 100 000 stars in the Milky Way, and another (PESSTO) is following up on transient objects such as supernovae using the New Technology Telescope at La Silla.

Some of these surveys began back in 2010, and some much more recently, but data from all of them are now being made public and are accessible to astronomers around the world through ESO's archive.

Although they are still in progress, the surveys are already allowing astronomers to make many discoveries.

Just a few of these new results include new star clusters found in the VVV survey, the best map yet of the central parts of our Milky Way, a very deep view of the infrared sky and, very recently, some of the most distant quasars discovered so far (from the VISTA VIKING - survey).

The ESO Public Surveys will continue for many years, and their astronomical legacy value will stretch many decades into the future.