A new image produced by the James Webb Space Telescope reveals new details of Stephan's Quintet, the very first compact galaxy group ever discovered that was featured in the 1946 film "It's a Wonderful Life."
I'm quite sure most readers of the column are familiar with the holiday classic "It's a Wonderful Life." If you aren't, it is a story about a fellow named George Bailey (Jimmy Stewart) who wants to travel and do great things but ultimately ends up running a building-and-loan association in a small community, all while married and locked in a constant struggle with the greedy old banker of the town. And when it finally looks as though the banker is about to drive him to ruin, George decides to commit suicide, whereupon an angel, in the nick of time, intercedes and shows him, in whimsical fashion, what the town would have been like without him. The vision is so distressing that George begs the angel to return him to his hopeless situation, and now with boundless joy is saved, also in the nick of time, by the financial assistance of his friends.
American film critic, Roger Ebert wrote (opens in new tab) of "It's a Wonderful Life" in 1999: "The corniest scenes in the movie — those galaxies that wink while the heavens consult on George's fate — work because they are so disarmingly simple. A more sophisticated approach might have seemed labored."
Behold! Stephan's Quintet
Ebert's "corny scenes" appears within the first couple of minutes of the start of the movie, where movie viewers are informally introduced to a cluster of five galaxies, known to astronomers as Stephan's Quintet — the very first compact galaxy group ever discovered. The group, visible in the constellation Pegasus the Flying Horse, was discovered by the French astronomer Édouard Stephan in 1877 at Marseille Observatory and is the most studied of all the compact galaxy groups.
But to call it a galaxy "quintet" is a bit of a misnomer, for the largest and brightest of the five — catalogued NGC 7320 — is merely an innocent bystander. While the other four galaxies — NGC 7317, NGC 7318A, NGC 7318B, and NGC 7319 – are located at roughly 290 million light-years away and form a true galaxy group, NGC 7320 is much closer to us (relatively speaking) at "only" 39 million light years.
In contrast, those other four galaxies are so close together that they have begun to interact with each other. They are bound by gravity and will eventually merge into one large elliptical galaxy in several million years. In fact, two of these galaxies — NGC 7318A and NGC 7318B — have already started to consolidate. The subsequent collision has drawn out long, sweeping tails of gas, dust and stars from each galaxy, in turn triggering massive bursts of star formation.
Ever since 1929, when Edwin Hubble discovered that our universe is expanding, we have known that most other galaxies are moving away from us. Light from these galaxies is shifted to longer (and this means redder) wavelengths - in other words, it is 'redshifted.' The redshift of a distant galaxy is easily measured by comparing its spectrum with a reference laboratory spectrum. Atomic emission and absorption lines occur at well-known wavelengths. By measuring the location of these lines in astronomical spectra, astronomers can determine the redshift of the receding sources.
Initially, however, the difference in distance between the assemblage of four of the galaxies in the Quintet versus the much closer fifth galaxy produced a conundrum among cosmologists and astrophysicists. Those four galaxies that are clustered together show a large redshift, corresponding to a recessional speed of 4,000 miles (6,400 km) a second. But galaxy NGC 7320, showed a redshift indicating a much slower speed of just 491 miles (790 km) per second. This indicated that the four galaxies were about seven times farther out in space compared to the fifth.
Astronomers wondered how that could be.
Indeed, visually, images seemed to show that NGC 7320 was connected to the other four members by faint tidal streamers. In addition, the degree of photographic resolution by the best 20th century observatory photographs seemed to imply that the other four members are not as remote as their redshift values would indicate.
So, if all five galaxies were physically related, then using redshift to determine stellar distances — which indicated that one galaxy of the Quintet is much closer compared to its other four companions — might be flawed. American astronomer Halton Arp (1927-2013) was one of those who believed for a long time that this was indeed the case.
Hubble to the rescue!
The Hubble Space Telescope finally solved this issue in 2000. Its superior imaging compared to Earthbound telescopes was able to bring out individual stars in NGC 7320 while the images of the other four galaxies remained starless.
So, it all ended up being just a happy coincidence: NGC 7320 appears the same size as its four companions because although it is actually much smaller than the other four it is also much closer; it just happens to be aligned with the other four galaxies as seen from our earthly perspective.
And the steamers emanating from it and seemingly interacting with the other four is an optical illusion as well.
Together, the five galaxies of Stephan's Quintet are also known today as the Hickson Compact Group 92 (HCG 92). This, in spite of the fact that NGC 7320 has no physical connection to the other four.
If you want to try and see the Quintet for yourself, extend an imaginary line from the star Mu Pegasi through Eta Pegasi and continue approximately the same distance beyond, A word of caution: these galaxies are not really targets for the beginner, as they need at least a 10-inch (250 mm) telescope to be seen clearly.
Enter James Webb
Now, once again, the five galaxies that were given prominence in a popular movie three-quarters of a century ago, are being spotlighted again thanks to the newest outer space observatory: The James Webb Space Telescope. Stephan's Quintet was among the very first objects that the brand new 21-foot (6.5 meter) telescope was turned to when it entered service on July 12th.
This latest Stephan's Quintet image is an enormous mosaic of nearly one-thousand images. It's Webb's largest image to date and contains over 150 million pixels utilizing by Webb's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). NIRCam's high-resolution imaging capability allowed Webb to see individual stars and the bright core of the foreground galaxy on the left side of the image. The galaxy at the top of the image harbors a supermassive black hole — or an active galactic nucleus — about 24 million times the mass of the sun. The supermassive black hole pulls in materials and produces light energy equivalent to about 40 billion suns.
Stephan's Quintet is an amazing "laboratory" to study how galaxies merging and interacting affect galactic evolution. According to a NASA statement, "Rarely do scientists see in so much 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."
Something for you to ponder the next time you watch "It's a Wonderful Life."
Indeed, the James Webb Telescope reveals Stephan's Quintet in a truly new light.
It's a wonderful image!
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium (opens in new tab). He writes about astronomy for Natural History magazine (opens in new tab), the Farmers' Almanac (opens in new tab) and other publications. Follow us on Twitter @Spacedotcom (opens in new tab) and on Facebook (opens in new tab).