Astronomers at the University of Arizona have identified five examples of a new class of star system. They are not exactly galaxies and only exist in isolation.
The new star systems contain only young, blue stars, which are distributed in an irregular pattern and appear to exist in surprising isolation from any potential parent galaxy.
The star systems – which astronomers say appear through a telescope as “blue blobs” and are the size of small dwarf galaxies – are located within the relatively nearby Virgo cluster of galaxies. The five systems are separated from any potential parent galaxies by more than 300,000 light-years in some cases, making their origins difficult to pinpoint.
Astronomers found the new systems after another research group, led by Elizabeth Adams of the Dutch Institute of Radio Astronomy, compiled a catalog of nearby gas clouds, providing a list of potential locations for new galaxies. After that catalog was published, several research groups, including one led by UArizona associate astronomy professor David Sand, began looking for stars that could be associated with these gas clouds.
The gas clouds were once thought to be associated with our own galaxy, and most of them probably are, but when the first collection of stars, called SECCO1, was discovered, astronomers realized it was not near the Milky Way, but rather in the Virgo cluster, which is much further away, but still very close in scale to the universe.
SECCO1 was one of the very unusual “blue bubbles,” said Michael Jones, a postdoctoral fellow at Arizona’s Steward Observatory and lead author of a study describing the new star systems. Jones presented the findings, which Sand co-authored, during the 240th meeting of the American Astronomical Society in Pasadena, California, on Wednesday.
“It’s a lesson in the unexpected,” Jones said. “When you’re looking for things, you won’t necessarily find what you’re looking for, but you might find something else very interesting.”
The team obtained its observations from the Hubble Space Telescope, the Very Large Array Telescope in New Mexico and the Very Large Telescope in Chile. Study co-author Michele Bellazzini of the Istituto Nazionale di Astrofisica in Italy led the analysis of the Very Large Telescope data and presented a companion paper focusing on this data.
Together, the team learned that most stars in each system are very blue and very young and that they contain very little atomic hydrogen gas. This is significant because star formation begins with atomic hydrogen gas, which eventually evolves into dense clouds of molecular hydrogen gas before turning into stars.
“We’ve observed that most systems don’t have atomic gas, but that doesn’t mean there’s no molecular gas,” Jones said. “Indeed, 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 combination of blue stars and lack of gas was unexpected, as was the lack of older stars in the systems. Most galaxies have older stars, which astronomers call “red and dead”.
“Stars that are born red are less massive and therefore live longer than blue stars, which burn fast and die young, so old red stars are usually the last ones left alive,” Jones said. “And they’re dead because they don’t have gas left to form new stars. These blue stars are like an oasis in the desert, basically.”
The fact that the new star systems are abundant in metals suggests how they might have formed.
“For astronomers, metals are any element heavier than helium,” Jones said. “This tells us that these star systems formed from gas that was taken from a large galaxy, because the way metals are built is by many repeated episodes of star formation, and you only get that in a large galaxy.” .
There are two main ways to extract gas from a galaxy. The first is tidal stripping, which occurs when two large galaxies pass each other and gravitationally strip away gas and stars.
The other is what is known as ram pressure stripping.
“It’s like you’re belly-flopping into a swimming pool,” Jones said. “When a galaxy’s belly falls into a cluster filled with hot gas, its gas is forced out from behind it. That’s the mechanism 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 become as isolated as they are, they must be moving very quickly, and the tidal stripping speed is low compared to the tidal pressure stripping. battering ram.
Astronomers hope that one day these systems will break up into individual star clusters and spread across the larger galaxy cluster.
What the researchers learned fuels the biggest “recycling history of gas and stars in the universe,” said Sand. “We think this belly-dropping process turns many spiral galaxies into elliptical galaxies at some level, so learning more about the general process teaches us more about galaxy formation.”
Hubble focuses on large lenticular galaxy 1023
Michael G. Jones et al, Young, blue, and isolated stellar systems in the Virgo Cluster. II. A new class of star system. arXiv:2205.01695v1 [astro-ph.GA]arxiv.org/abs/2205.01695
Provided by the University of Arizona
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