Science

James Webb Space Telescope finds powerful shock wave and small dwarf galaxy in Stefan’s Quintet

The shock waves created by the collision between the Stefan Quintet galaxies and the intruder galaxy are causing strange processes in the intergalactic medium, rarefied clouds of hot hydrogen plasma that exist in the space between the galaxies.

New observations made with the James Webb Space Telescope (Webb or JWST) and the Atacama Large Millimeter/Submillimeter Array (ALMA) have given astronomers a good view of the intruder galaxy NGC 7318b, which is furiously blasting its way into this group of galaxies at relative speed. about 1.8 million miles per hour (about 800 kilometers per second). This is enough to get from the Earth to the Moon and back in just 15 minutes.

This violent intrusion into Stephen’s Quintet causes a shock wave several times the size of the Milky Way, which travels through interstellar plasma and sets off a “refinery” of warm and cold molecular hydrogen gas between five galaxies. In addition, astronomers have found that the giant gas cloud is breaking apart to form a less dense “fog” of warm gas; The JWST/ALMA observations also show a warm gas tail formed as a result of the collision of two clouds and even the formation of a new galaxy.

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The discovery of these phenomena could help scientists better understand how turbulence affects the intergalactic medium and how collisions affect the formation of stars and the evolution of galaxies in general.

“When this intruder crashes into the group, it collides with an old gas streamer, which was likely caused by a previous interaction between two other galaxies, and causes a giant shock wave to form,” said Philip Appleton, lead astronomer for the project. and a senior fellow at the California Institute of Technology’s (IPAC) Infrared Processing and Analysis Center, the statement said. (will open in a new tab)

“As the shock wave passes through this lumpy streamer, it creates a very turbulent or unstable cooling layer, and it is in the regions affected by this violent activity that we observe unexpected patterns and recirculation of gaseous molecular hydrogen,” Appleton. said. “This is important because molecular hydrogen forms the raw material from which stars can eventually form, so understanding its fate will tell us more about the evolution of the Stefan Quintet and galaxies in general.”

Located about 270 million light-years from Earth in the constellation Pegasus, Stephan’s Quintet consists of the galaxies NGC 7317, NGC 7318a, NGC 7318b, NGC 7319 and NGC 7320. The five galaxies have proven to be the perfect laboratory for studying galactic interactions. , including violent encounters and how these interactions affect the environment.

NASA’s James Webb Space Telescope reveals never-before-seen details of the Stephen’s Quintet group of galaxies. (Image credit: NASA, ESA, CSA and STScI)

But Stephan’s Quintet is different from other galactic collision sites because these mergers usually trigger bouts of intense star formation, which does not occur in these five galaxies. Instead, in Stefan’s quintet, the turbulence of these galactic collisions is felt in an intergalactic medium where there is not enough raw material to trigger star birth.

This means that the turbulence caused by the collision is not masked by star formation, which means that astronomers get an unobstructed view of NGC 7318b as it quickly bursts into Stefan’s Quintet.

Seizing this opportunity, Appleton and his team zoomed in on three key regions of Stephen’s Quintet using ALMA, an astronomical interferometer of 66 radio telescopes in the Atacama Desert region of northern Chile. The observations have allowed astronomers to build the first ever clear picture of how hydrogen gas is constantly moving and taking shape.

“The power of ALMA is evident in these observations, providing astronomers with new insights and a better understanding of these previously unknown processes,” Joe Pesce, ALMA program manager at the US National Science Foundation, said in the same statement.

Read more: 8 interesting facts about the ALMA telescope

Atacama Large Millimeter/Submillimeter Grating (ALMA)

(Image credit: ALMA (ESO/NAOJ/NRAO), V. Garnier (ALMA))

Study of three areas of turbulence

At the center of the main shock wave, in an area labeled Field 6, a giant cloud of cold molecules collapses and turns into a tail of warm molecular hydrogen. As the same processes continue, hydrogen repeatedly recycles through phases with the same temperature.

“What we’re seeing is the disintegration of a giant cloud of cold molecules in a super-hot gas, and interestingly, the gas doesn’t take a hit, it just goes through warm and cold phases,” Appleton said. “We don’t fully understand these cycles yet, but we do know that the gas is recycled because the tail is longer than the time it takes for the clouds it’s made of to break down.”

This hydrogen “refinery” isn’t the only strange thing these shockwaves are causing. In an area called Field 5, the team found two cold gas clouds connected by a stream of warm molecular hydrogen gas. One of the clouds is shaped like a bullet and pierces this thread, forming a ring-shaped structure.

“Molecular clouds penetrating intergalactic gas and leaving chaos in their wake may be rare and not yet fully understood,” said Bjorn Emonts, an astronomer at the National Radio Astronomy Observatory (NRAO) and co-investigator of the project. the same statement. “

But our data show that we have taken the next step in understanding the shocking behavior and exuberant life cycle of molecular gas clouds in the Stefan quintet.”

Of the areas explored by the team, Field 4 appears to be the most “normal” and serene, containing a less turbulent environment in which hydrogen gas collapses, causing the creation of a stellar disk. The team believes this marks the beginning of the formation of a small dwarf galaxy in Field 4.

“In Field 4, it is likely that pre-existing large clouds of dense gas became unstable due to the impact and collapsed to form new stars, as we would expect,” said Pierre Guillard, a researcher at the Institute of Astrophysics in Paris. in France and co-investigator of the project, the same statement said. “The shock wave in the intergalactic medium of Stephan’s Quintet has formed the same amount of cold molecular gas as in our own Milky Way, and yet it is forming stars much more slowly than expected.”

Gillard believes that these new observations are important for theoretical models of the effects of turbulence in the universe. However, he added that more work would be needed to understand the impact of high-level turbulence and how hot and cold gas mix.

While the JWST Stefan Quintet images combined with ALMA observations have provided a wealth of information about the relationship between cold, warm molecular and ionized hydrogen gas after the giant shockwave, the team will have to turn to spectroscopic data to get more details. a complete overview of the region.

“These new observations gave us some answers, but ultimately showed how much we still don’t know,” Appleton said. “While we now have a better understanding of gas structures and the role of turbulence in creating and maintaining them, future spectroscopic observations will allow us to follow the movement of gas through the Doppler effect, tell us how fast warm gas moves, allow us to measure the temperature of warm gas and see how the gas cools. or heated by shock waves. In fact, we have one side of the story. Now it’s time to get to know another.”

The group’s findings were presented at the 241st meeting of the American Astronomical Society on Monday (January 9).

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