When Star Clusters Collide: Hubble
August 16, 2012

Hubble Captures Potential Star Cluster Collision

Watch the Video: Simulation of Star Clusters Encounter

Lee Rannals for redOrbit.com - Your Universe Online

The Hubble Space Telescope has been keeping its eyes fixed on two clusters full of massive stars that may be in the early stages of merging.

The star clusters are about 170,000 light-years away in the Large Magellanic Cloud, which is a small satellite galaxy to our Milky Way.

What was thought to have been just one cluster in the star-forming region commonly referred to as the Tarantula Nebula is actually a composite of two clusters that differ in age by about a million years.

The 30 Doradus complex has been an active star-forming region for 25 million years. It is currently unknown how much longer this region can continue to create new stars.

Smaller systems that merge into larger ones help to explain the origin of some of the largest known star clusters.

Astronomers were looking at the area while searching for runaway stars, which are fast-moving stars that have been kicked out of their stellar nurseries.

"Stars are supposed to form in clusters, but there are many young stars outside 30 Doradus that could not have formed where they are; they may have been ejected at very high velocity from 30 Doradus itself," lead scientist Elena Sabbi of the Space Telescope Science Institute said.

She noticed something unusual during the team's search while looking at the distribution of the low-mass stars. The astronomers found that the cluster was not spherical, but had features similar to the shape of two merging galaxies.

Giant gas clouds, out of which star clusters form, can start to fragment into smaller pieces, and once those pieces precipitate stars, they begin to interact and merge to become a bigger system. The astronomers believe this model is what is happening in 30 Doradus.

The runaway stars were expelled from the core of 30 Doradus as the result of dynamical interactions. These interactions are common during a process called core collapse, which is when more-massive stars sink to the center of a cluster by dynamical interactions with lower-mass stars.

When massive stars have reached the core, they become unstable and eject each other from the cluster.

The big cluster R136 in the center of the 30 Doradus region is too young to have experienced a core collapse. However, astronomers believe that due to the large number of runaway stars, it seems as though a small cluster has merged into R136.

Astronomers will have to perform follow-up studies to look at the area in more detail and on a larger scale to see if any more clusters might be interacting with the ones observed.

The James Webb Space Telescope being developed by NASA will allow scientists to look deep into the regions of the Tarantula Nebula in visible-light photographs. This telescope will help better reveal the underlying population of stars in the nebula.

The 30 Doradus Nebula is interesting to astronomers because it is a good example of how star-forming regions in the young universe may have looked.

Results are published in Science.