ALMA Witnesses Galactic ‘Rope Play’ and the ‘Cry’ of a ‘Baby Star’


ALMA not only witnessed a galactic “string game” between merging galaxies, but also discovered the “scream” of the birth of a “baby star” in the Small Magellanic Cloud.

As they watched a newly sleeping galaxy using the SOUL (Atacama Large Millimeter/submillimeter Array) and the Hubble Space Telescope, scientists found that it had stopped forming stars, not because it had run out of gas, but because most of its fuel from star formation had been expelled from the system. merge with another galaxy.

The result is new to ALMA scientists. Plus, if found to be common, the findings could change the way scientists think about galaxy mergers and deaths.

As galaxies move through the Universe, they sometimes encounter other galaxies. When they interact, the gravity of each galaxy pulls on the other. the following “rope game” it flings gas and stars away from galaxies, leaving behind streams of matter known as tidal tails.

And that’s exactly what scientists think happened to SDSS J1448+1010, but with a twist in the story. The massive galaxy, which originated when the Universe was about half its current age, has nearly completed its merger with another galaxy.

During observations with Hubble and ALMA, scientists discovered tidal tails containing about half of all cold star-forming gas in the system. The discovery of the forcibly rejected material – equal to 10 billion times the mass of our Sun – indicated that fusion may be responsible for ‘stopping’ star formationwhat scientists did not expect.

“What initially made this massive galaxy interesting was that for some reason it suddenly stopped forming stars about 70 million years ago, immediately after a burst of star-forming activity. stars. Most galaxies are happy to keep forming stars,” said Justin Spilker, an astronomer at Texas A&M University and lead author of the paper.

“Our observations with ALMA and with Hubble have proven that the real reason the galaxy stopped forming stars is that the smelting process ejected about half of the combustible gas, available for star formation, for intergalactic space. Without fuel, the galaxy could not continue to form stars,” he added.

This discovery sheds light on the processes by which galaxies live or die and helps scientists better understand their evolution.

“When we look at the Universe, we see some galaxies actively forming new stars, like our own Milky Way, and some not. But those ‘dead’ galaxies have a lot of old stars, so they must have formed all those stars at some point and then stopped creating new ones,” said Wren Suess, a cosmology colleague at the University of California, Santa Cruz, and co. – author of the scientific article. .

“We still don’t understand all of the processes that prevent galaxies from forming stars, but this discovery shows how powerful these great galactic mergers are and how much they can affect how a galaxy grows and changes over time,” he added.

Since the new result comes from a single observation, it is currently unclear how typical this “string play” and the resulting quietness might be. However, the discovery challenges long-held theories about how stars form and galaxies die and has given scientists an exciting new challenge: to find more examples.

“While it is clear from this system that cold gas can actually end up far beyond a fusion system and ‘extinguish’ a galaxy, the sample size, a single galaxy, tells us very little about the frequency of this process”said David Setton, a student in the Department of Physics and Astronomy at the University of Pittsburgh and co-author of the paper.

“But there are many galaxies, like J1448+1010, that we can catch right in the middle of these crashes and study exactly what happens to them as they go through this phase. Cold gas ejection is an exciting new piece of the quiescence puzzle, and we are excited to try and find more examples”Underline.

Spilker added: “Astronomers thought the only way to stop galaxies from forming stars was through violent and rapid processes, like many supernovae exploding in the galaxy to blow out most of the gas and heat up the rest. Our observations show that it does not take a “seeing” process to cut off star formation. The much slower fusion process could also put a stop to star and galaxy formation.

“Crying” for the birth of a “baby star”

The heavy elements of interstellar matter have a significant impact on the mechanism of star formation. In the early Universe, the abundance of heavy elements was lower than in the current Universe, because there had not yet been enough time for nucleosynthesis to produce heavy elements in stars. How star formation in such an environment differs from actual star formation has not been well understood.

An international team led by Professor Toshikazu Onishi of Osaka Metropolitan University and Assistant Professor Kazuki Tokuda of Kyushi University/NAOJ used ALMA to to observe young, high-mass stellar objects in the Small Magellanic Cloud.

The Small Magellanic Cloud is characterized by a low abundance of elements heavier than helium, similar to galaxies of 10 billion years ago. The target provides a detailed observational view thanks to its relatively close distance to Earth. In this study, the researchers detected a flow of bipolar gas exiting the “star baby” Y246 and determined that the molecular flow has a speed greater than 54,000 km/h in both directions.

In the current Universe, growing “baby stars” are thought to have their spin suppressed by this molecular flow during gravitational contraction, accelerating the growth of the star. The discovery of the same phenomenon in the Small Magellanic Cloud suggests that this star formation process has been common for the past 10 billion years. The team also hopes that this discovery will bring new perspectives to the study of stars and planetary formation.

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