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Young Stars in Dwarf Objects in a Hostile Galaxy Cluster Enviroment

Steward Postdoctoral Research Associate Michael Jones and Associate Professor David Sand have identified five instances of a new type of stellar system. You can see three images HERE and HERE and HERE. They are around a million times less massive than our galaxy, likely containing only 10,000 to 100,000 stars, which are arranged in a clumpy and irregular configuration. These systems, colloquially referred to as "blue blobs", are dominated by young, blue stars, yet are surprisingly isolated, typically over 300,000 lightyears from the nearest plausible parent galaxy. Furthermore, all five reside in the nearby Virgo galaxy cluster (approximately 50 million lightyears away). Galaxy clusters are filled with hot ionized gas at millions of degrees, making them an extremely hostile environment for the cold gas that is needed to form new stars. Even relatively large galaxies, similar in mass to our own Milky Way, rapidly lose their cold gas content after falling into a galaxy cluster. Yet these tiny "blue blobs" are floating alone, embedded in this hostile, hot medium, and are actively forming new stars. This raises the questions, where did they come from and how did they manage to become isolated while still so young.

To answer these questions Dr. Jones,  Prof. Sand and Professor Kristine Spekkens (RMC, Kingston, Ontario) obtained Hubble Space Telescope and Very Large Array imaging of these systems, as well as observations with the Very Large Telescope in Chile, in collaboration with Dr. Michele Bellazzini (INAF, Bologna, Italy). These observations indicated that the "blue blobs" are rich in heavy elements, which is strong evidence that they formed from gas stripped from a large galaxy that had accumulated these elements as it built up its stellar mass over a long history. Material can be stripped from galaxies in two main ways, tidal stripping and ram pressure stripping. Tidal stripping occurs when two galaxies pass close by each other (or even merge) and their gravity pulls apart their outskirts, resulting in long tails of stripped material. Ram pressure stripping occurs when a galaxy moves rapidly through a gas medium, which forces its own gas out behind it. In either scenario, stripped gas clouds can collapse and form new stellar systems, analogous to "blue blobs." However, ram pressure stripping when galaxies fall into a cluster can occur at very high velocity (higher than can be achieved with tidal stripping) and this offers an explanation for how such young objects can be so isolated; they are just moving at very high speeds, perhaps over 500 miles per second.

These results were presented on Wednesday June 15th at a AAS 240 press briefing, and an accompanying UA press release. Check these out for more details.

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