Stephan’s Quintet (MIRI Imaging)

With its powerful, mid-infrared vision, MIRI shows never-before-seen details of Stephan’s Quintet, a visual grouping of five galaxies. MIRI pierced through dust-enshrouded regions to reveal huge shock waves and tidal tails, gas and stars stripped from the outer regions of the galaxies by interactions. It also unveiled hidden areas of star formation. The new information from MIRI provides invaluable insights into how galactic interactions may have driven galaxy evolution in the early universe.

This image contains one more MIRI filter than was used in the NIRCam-MIRI composite picture. The image processing specialists at the Space Telescope Science Institute in Baltimore opted to use all three MIRI filters and the colours red, green and blue to most clearly differentiate the galaxy features from each other and the shock waves between the galaxies.

In this image, red denotes dusty, star-forming regions, as well as extremely distant, early galaxies and galaxies enshrouded in thick dust. Blue point sources show stars or star clusters without dust. Diffuse areas of blue indicate dust that has a significant amount of large hydrocarbon molecules. For small background galaxies scattered throughout the image, the green and yellow colours represent more distant, earlier galaxies that are rich in these hydrocarbons as well.

Stephan’s Quintet’s topmost galaxy – NGC 7319 – harbours a supermassive black hole 24 million times the mass of the Sun. It is actively accreting material and puts out light energy equivalent to 40 billion Suns. MIRI sees through the dust surrounding this black hole to unveil the strikingly bright active galactic nucleus.

As a bonus, the deep mid-infrared sensitivity of MIRI revealed a sea of previously unresolved background galaxies reminiscent of Hubble’s Deep Fields.

Together, the five galaxies of Stephan’s Quintet are also known as the Hickson Compact Group 92 (HCG 92). Although called a “quintet,” only four of the galaxies are truly close together and caught up in a cosmic dance. The fifth and leftmost galaxy, called NGC 7320, is well in the foreground compared with the other four. NGC 7320 resides 40 million light-years from Earth, while the other four galaxies (NGC 7317, NGC 7318A, NGC 7318B, and NGC 7319) are about 290 million light-years away. This is still fairly close in cosmic terms, compared with more distant galaxies billions of light-years away. Studying these relatively nearby galaxies helps scientists better understand structures seen in a much more distant universe.

This proximity provides astronomers a ringside seat for witnessing the merging of and interactions between galaxies that are so crucial to all of galaxy evolution. Rarely do scientists see in so much exquisite detail how interacting galaxies trigger star formation in each other, and how the gas in these galaxies is being disturbed. Stephan’s Quintet is a fantastic “laboratory” for studying these processes fundamental to all galaxies.

Tight groups like this may have been more common in the early universe when their superheated, infalling material may have fueled very energetic black holes called quasars. Even today, the topmost galaxy in the group – NGC 7319 – harbours an active galactic nucleus, a supermassive black hole that is actively pulling in material.

MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

For a full array of Webb’s first images and spectra, including downloadable files, please visit: https://esawebb.org/initiatives/webbs-first-images/