'Billiards table' of star collision revealed

Scientists have imaged a cluster of stars, heavily obscured by material in our galaxy, where stars are so densely packed that it is likely a rare environment where stars can collide.

It's a bit like a stellar billiards table; where the probability of collisions depends on the size of the table and on the number of billiard balls on it, said Francesco R. Ferraro of the University of Bologna (Italy), one of the team members who used the Gemini Observatory to make the observations.

The cluster of stars, known as Liller 1, is a difficult target to study due to its distance and also because it is located close to the center of the Milky Way (about 3,200 light-years away from it), where the obscuration by dust is very high.

The unprecedented ultra-sharp view of the cluster reveals a vast city of stars estimated by the team to contain a total mass of at least 1.5 million suns, very similar to the most massive globular clusters in our galaxy: Omega Centauri and Terzan 5.

Although our galaxy has upwards of 200 billion stars, there is so much vacancy between stars that there are very few places where suns actually collide, said principal investigator Douglas Geisler, adding that the congested overcrowded central regions of globular clusters are one of these places. Our observations confirmed that, among globular clusters, Liller 1 is one of the best environments in our galaxy for stellar collisions.

Liller 1 is a tight sphere of stars known as a globular cluster. Globular clusters orbit in a large halo around the center, or nucleus, of our galaxy and many of the closer globular clusters are spectacular showpieces, even in small telescopes or binoculars.

This isn't one of these showpieces; it is so obscured by material in the central bulge of our galaxy that is almost completely invisible in visual light, observed lead author Sara Saracino.

The observations of the tightly packed cluster used Gemini Observatory's powerful adaptive optics system at the Gemini South telescope in Chile.