Astronomers have discovered a new class of stellar systems. Known as blue blobs, these collections are rich in blue stars and are the size of tiny dwarf galaxies – although, unlike those, they don’t appear to be very close to any big galaxy.
That’s not all – the galaxies tend to lack older stars which suggests that they are very young systems, but they also lack atomic gas. Given the young age of the stars and lack of atomic gas, it means that these blobs lost some of their gas very recently.
One explanation favored by the researchers is that they did a cosmic belly flop (technically known as ram pressure stripping). The findings can be read in a paper available on the ArXiv.
"This is like if you belly flop into a swimming pool," lead author Michael Jones, a postdoctoral fellow in the University of Arizona Steward Observatory said in a statement. "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 research suggests that these systems are moving very fast, consistent with the observations that they are isolated from larger galaxies, and they have lost most of their atomic gas while still holding onto their molecular gas. The findings were presented at the 240th meeting of the American Astronomical Society, which took place last week in California.
The team did not set out to find weird congregations of stars. Their project looked at gas clouds in the neighborhood of the Milky Way in the hope of finding new dwarf galaxies there, and was followed up by findings of stars associated with these gas clouds. While many of these clouds are probably still near our galaxy, the first group of stars spotted within one of these ended up being in the Virgo cluster. Definitely not next to the Milky Way.
"It's a lesson in the unexpected," Jones said. "When you're looking for things, you're not necessarily going to find the thing you're looking for, but you might find something else very interesting."
Ram pressure stripping is believed to be an important process in the evolution of galaxies, as it can impact galaxies entering into clusters following cluster collisions and other processes.
"We think that this belly flopping process changes a lot of spiral galaxies into elliptical galaxies on some level, so learning more about the general process teaches us more about galaxy formation."