Mysterious 'Blue Blobs' Reveal a New Kind of Star System
hubie writes:
University of Arizona astronomers have identified five examples of a new class of stellar system. They're not quite galaxies and only exist in isolation.
The new stellar systems contain only young, blue stars, which are distributed in an irregular pattern and seem to exist in surprising isolation from any potential parent galaxy.
The stellar systems - which astronomers say appear through a telescope as "blue blobs" and are about the size of tiny dwarf galaxies - are located within the relatively nearby Virgo galaxy cluster. The five systems are separated from any potential parent galaxies by over 300,000 light years in some cases, making it challenging to identify their origins.
[...] "We observed that most of the systems lack atomic gas, but that doesn't mean there isn't molecular gas," Jones said. "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."
[...] The fact that the new stellar systems are abundant in metals hints at how they might have formed.
"To astronomers, metals are any element heavier than helium," Jones said. "This tells us that these stellar systems formed from gas that was stripped from a big galaxy, because how metals are built up is by many repeated episodes of star formation, and you only really get that in a big galaxy."
There are two main ways gas can be stripped from a galaxy. The first is tidal stripping, which occurs when two big galaxies pass by each other and gravitationally tear away gas and stars.
The other is what's known as ram pressure stripping.
"This is like if you belly flop into a swimming pool," Jones said. "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 prefers the ram pressure stripping explanation because in order for the blue blobs to have become as isolated as they are, they must have been moving very quickly, and the speed of tidal stripping is low compared to ram pressure stripping.
Journal Reference:
Michael G. Jones, David J. Sand, Michele Bellazzini et al., Young, blue, and isolated stellar systems in the Virgo Cluster. II. A new class of stellar system, arXiv:2205.01695 [astro-ph.GA]
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