Mysterious ‘blue bubble’ reveals new type of star system

Mysterious ‘blue bubble’ reveals new type of star system

Astronomers at the University of Arizona (USA) have identified five examples of a new class of star systems. They’re not exactly galaxies, they just exist in isolation.

The team obtained observations from the Hubble Space Telescope, the Very Large Array Telescope (VLA) in New Mexico (USA), and the Very Large Telescope (VLT) in Chile. Another co-author of the study, Michele Bellazzini of the Italian National Institute for Astrophysics, led the analysis of the VLT data and published a companion paper focusing on the data.

unexpected combination

The astronomers found that most of the stars in each system were very blue and very young, and contained very few atoms of hydrogen gas. This is important because star formation begins with atomic hydrogen gas, which later evolves into a dense cloud of molecular hydrogen gas before becoming a star.

“We observed that most systems do not have atomic gas, but that doesn’t mean there is no molecular gas,” Jones said. “Indeed, there must be some molecular gas because they are still forming stars. The presence of mostly young stars and a small amount of gas suggests that these systems must have lost gas recently.”

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

“Stars born red are less massive and therefore live longer than blue stars, which burn faster and die earlier. So old red stars are usually the last ones alive,” Jones said. “They’re dead because they don’t have the gas left to form new stars. These blue stars are basically like oasis in the desert.”

training track

The fact that new star systems are rich in metals suggests how they might have formed.

“To astronomers, a metal is any element heavier than helium,” Jones said. “This tells us that these star systems formed from gas extracted from a large galaxy, because the way metals are built through repeated star formation processes that you only get in a large galaxy. “

There are two main methods of extracting gas from galaxies. The first is tidal forces, which occur when two large galaxies pass each other and gravitationally pull gas and stars out. The other is called resistance pressure.

“It’s like you’re tumbling in a swimming pool,” Jones said. “When a galaxy’s belly falls into a hot gas-filled star cluster, its gas is squeezed out from behind it. That’s the mechanism we think we’re seeing here for creating these objects.”

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