Telescopes Reveal a Frenzy of Gas in Stephan’s Quintet

Data from Webb Space Telescope and ALMA reveals more about a group of five galaxies.

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Stephan's Quintet as seen by Webb (background) and ALMA (foreground).
Stephan’s Quintet as seen by Webb (background) and ALMA (foreground).
Image: ALMA (ESO/NAOJ/NRAO)/JWST/ P. Appleton (Caltech), B.Saxton (NRAO/AUI/NSF)

Analysis of Stephan’s Quintet, a vivid set of galaxies in the distant universe, by two telescopes has revealed details of how the galaxies (and the hydrogen gas within them) interact.

One of the galaxies in the quintet is rapidly intruding on the others’ personal space, producing a shockwave in the region traveling at about 500 miles per second. A recent research team found clouds colliding, a system with a tail, and a possible dwarf galaxy being formed.

The galaxies were observed by two large observatories—one on land and one a million miles from Earth. In Chile, the Atacama Large Millimeter/submillimeter Array (ALMA) gazed at the radio emissions from the quintet. At L2, a point in space that allows objects to stay put with minimal fuel burn, the Webb Telescope looked at the quintet at infrared and near-infrared wavelengths.


Stephan’s Quintet is a group of five galaxies that appear very close together in the night sky. One of the galaxies is in the foreground from our view, and it does not interact with the other galaxies in the quintet. They’re about 270 million light-years from Earth and were included in Webb’s first image release on July 12.

Webb’s image of the quintet is remarkably detailed, comprising 150 million pixels’ worth of data about the distant group. The ALMA images focused on specific regions of the quintet that the research team deemed of particular scientific interest.


The results of the observations are a sweeping composite portrait, with more detailed images (insets in the image above) showing hotspots of activity within the galactic troupe. The astronomical team’s results were announced in a press conference at a meeting of the American Astronomical Society today.

“The shock wave in the intergalactic medium of Stephan’s Quintet has formed as much cold molecular gas as we have in our own Milky Way, and yet, it forms stars at a much slower rate than expected,” said Pierre Guillard, a researcher at the Institut d’Astrophysique de Paris and a co-author of the study, in a NRAO release. “Understanding why this material is sterile is a real challenge for theorists. Additional work is needed to understand the role of high levels of turbulence and efficient mixing between the cold and hot gas.”


“The mystery is partially solved,” said Philip Appleton, an astronomer at the California Institute of Technology and a co-author of the paper, durin the press conference. “The intergalactic medium of Stephan’s Quintet is not uniform, but is a complex mix of warm, cold, and ionized gas.”

Taken in tandem, the Webb and ALMA images showcase how hot and cold hydrogen gas in the galaxies interacts, creating new galactic-scale structures, like long tails on the galaxies’ edges. (Webb’s sight is very useful for studying hot hydrogen molecules, and ALMA is good at seeing very cold hydrogen.) The ALMA data also revealed kinematics of the system, showing how turbulent the cold gas was.


As new Webb images get released, we get to enjoy them more than once: at first view, and then again later, when scientists have had a chance to comb through the data for cosmic clues.

More: Webb Telescope Spots Ancient Galaxy Built Like the Milky Way