Astronomers have discovered bizarre “blue blobs” in space. These blobs are clusters of young, blue stars that are isolated from any parent galaxy, suggesting they formed from a galactic “belly flop.”
Five of these blue blobs, as they appear in telescope images, were found in the Virgo galaxy cluster, using observations from Hubble and the Very Large Array. They seem to be a new type of stellar system composed of only young, blue stars, spread out in an irregular pattern. That’s a fairly strange arrangement – how they became isolated from any older stars was a mystery. And isolated they were, since the closest possible parent galaxy was hundreds of lightyears away.
On closer inspection, the team found more oddities about the blue blobs. Spectroscopy revealed that there was very little atomic hydrogen gas in the systems, which is strange because that’s a key ingredient for forming stars.
"We observed that most of the systems lack atomic gas, but that doesn't mean there isn't molecular gas," said Michael Jones, lead author of the study. "In fact, there must be some molecular gas because they are still forming stars. The existence of mostly young stars and little gas signals that these systems must have lost their gas recently.”
These young stars were also found to be high in heavy metals, indicating the systems had started off inside much larger galaxies where there had already been a few generations of star birth and death. But their young age and their isolation from any possible parent galaxies indicated they lost that gas very quickly. As such, the astronomers hypothesize that this occurred through a process called ram pressure stripping.
"This is like if you belly flop into a swimming pool," said Jones. "When a galaxy belly flops into a cluster that is full of hot gas, then its gas gets forced out behind it. That's the mechanism that we think we're seeing here to create these objects.”
The team predicts that eventually, these blue stellar systems are likely to split off into smaller clusters of stars, before spreading out further into the Virgo cluster.
The research has been submitted for publication in the Astrophysical Journal.
Source: University of Arizona
