New class of star system resulting from galactic "blinking"


Astronomers have identified five examples of a new class of star system, made up of young blue stars in an irregular pattern. and that they seem to exist isolated from any galaxy.

The mechanism by which they are born is similar to dropping the womb into a swimming pool, in this case a galaxy. falling on a mass of hot gas.

Star systems, the size of small dwarf galaxies, are located in the galaxy cluster relatively close to Virgo. The five systems are separated from any possible parent galaxy by more than 300,000 light years in some cases, which makes it difficult to identify its origins.

Astronomers at the University of Arizona discovered the new systems after another research group, led by Elizabeth Adams of the Netherlands Institute for Radio Astronomy, compiled a catalog of nearby gas clouds. , providing a list of potential sites for new galaxies. Once this catalog was published, several research groups, including one led by University of Arizona Associate Professor of Astronomy David Sand, they started looking for stars that might be associated with these gas clouds.

The gas clouds were thought to be associated with our own galaxy, and most likely are, but when the first collection of stars, called SECCO1, was discovered, astronomers realized it wasn’t. not near the Milky Way, but rather in the Virgo cluster, which is much further away but still very close on the scale of the universe.

SECCO1 was one of the very unusual “blue dots”, he said. it’s a statement Michael Jones, postdoctoral fellow at the UArizona Steward Observatory and lead author of a study describing new star systems. Jones presented the results, co-authored by Sand, at the 240th meeting of the American Astronomical Society.

The team got their 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 the data.

Together, the team learned that most stars in each system are very blue and very young, and contain very little atomic hydrogen gas. This is important because star formation begins with atomic hydrogen gas, which eventually it becomes dense clouds of molecular hydrogen gas before becoming stars.

“We see that most systems lack atomic gas, but that doesn’t mean there isn’t molecular gas,” says Jones. “In fact, there must be molecular gas because the stars are still forming. The existence of mostly young stars and little gas indicates that these systems must have recently lost their gas.”

The combination of blue stars and a lack of gas was unexpected, as was the absence of older stars in the systems. Most galaxies have older stars, which astronomers call “red and dead.”

“Stars that are born red have lower mass and therefore live longer than blue stars, which burn up quickly and die young, so old red stars are often the last to remain alive,” Jones said. “And they’re dead because they’ve run out of gas to form new stars. These blue stars are basically like an oasis in the desert.”

The fact that the new star systems were 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 sucked out of a large galaxy, because the way the metals accumulate is due to many repeated episodes of star formation, and that ‘we only really enter one large galaxy.

There are two main ways to extract gas from a galaxy. The first is tidal detachment, which occurs when two large galaxies intersect and gravitationally pull gas and stars apart.


The other is what is called dynamic pressure extraction. “It’s like falling into a pool on your stomach,” Jones said. “When the belly of a galaxy falls into a cluster filled with hot gas, its gas is ejected behind it. This is the mechanism we think we see here for creating these objects.”

The team prefers the dynamic pressure extraction explanation because for the blue dots to become as isolated as they are, they had to move very quickly, and the rate of tidal extraction is low compared to ram pressure extraction.

Astronomers hope that one day these systems will eventually split into individual star clusters and spread out into the larger cluster of galaxies.

What the researchers learned fuels the “biggest story of gas and star recycling in the universe,” Sand said. “We believe that this belly-falling process transforms many spiral galaxies into elliptical galaxies at some level, so knowing more about the global process tells us more about galaxy formation.”

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