Hubble Observes Mysterious Blue Star Clusters

Located at about 12 million light years away in the so-called Arp's Loop, the strange stellar structures are wondering alone through intergalactic space, while most stellar clusters are usually included into galaxies or orbit in their vicinity. It seems that these particular clusters have originated from a galactic collision between three known galaxies, more than 200 million years ago, and have masses equivalent to at least a thousands times that of the Sun.

Previously, astronomers believed that such collisions are not powerful enough to ejects sufficient matter, and later the cloud of gas would be dense enough to create a small star cluster, but the remnants of the triple collision between the galaxies M81, M82 and NGC 3077 located in the Ursa Major constellation proved them wrong, as the mass of the star clusters is approximated to be at least five times greater than the Orion Nebula in our galaxy.

They do not appear to belong to any particular galaxy and the stars in their constitution shine a brilliant blue light, suggesting that they are no more than 10 million years old, while our Sun has been burning hydrogen for the last 4.6 billion years. Duilia de Mello from NASA's Goddard Space Flight Center argues that the mass accumulation is most likely the outcome of a collision between the galaxies surrounding the brilliant star clusters, which ejected massive quantities of gas during the gravitational interactions that took place between them.

Interactions between galaxies are quite common in the universe, but could have been much more frequent during the early stages of the universe's life. Collisions would increase the gas cloud density between galaxies and trigger a star formation process, similar to that observed in Arp's Loop. As stars in the star clusters burn out their hydrogen fuel and explode into supernovae, they would spread the fused heavier elements into intergalactic space, process which is further simplified in the case of such lone clusters wondering through intergalactic space.