Hubble Space Telescope’s 32nd Anniversary Photo Features Dramatic Galaxy Cluster

The five galaxies, dubbed the Hickson Compact Group 40, will merge in roughly a billion years

A space image of five galaxies clustered together
The Hickson Compact Group 40 features five galaxies caught in a gravitational dance. NASA, ESA, STScI, Alyssa Pagan

Since its launch in 1990, the Hubble Space Telescope has captured the most stunning photographs across the galaxy. It has snapped portraits of giant planets like Jupiter and Saturn, imaged dream-like nebulas, and more—providing astronomers with the information needed to make amazing discoveries about the universe.

In honor of the telescope's 35th anniversary on April 24, NASA released a snapshot of five galaxies called The Hickson Compact Group 40 (HCG). The group is tightly nestled into a region of space that is less than twice the diameter of the Milky Way's stellar disk. Experts suspect the quintet is in the process of merging into a single giant elliptical galaxy, reports Space.com's Elizabeth Howell. The merge is expected to take a billion years, and the image gives researchers a chance to study galactic evolution.

The cluster features three spiral-shaped galaxies surrounded by orange dust clouds, a lens-like galaxy on the lower right, and an elliptical galaxy towards the top, all caught in a compact gravitational dance, Science Alert's David Nield reports. While tight groups of galaxies are not rare, they are mostly found at the heart of larger galaxy clusters. However, HCG is near the constellation Hydra and sits unusually isolated from anything else, making it an exciting target of study, a statement explains.

Over 100 compact galaxy groups have been spotted during sky surveys going back several decades, but the quintet is the most densely packed. Astronomers suspect that tightly packed groups were more common in the early universe and provided fuel for powering black holes, per a statement.

Scientists suspect that HCG may have formed this way because of the galaxies' dark matter, or the substances which interact mainly via gravity with visible matter. Once the starry regions come closer together, the dark matter can develop into a cloud covering the group that slows the galaxies down, per Science Alert. When the galaxies lose energy, they will fall together. Studying densely packed galaxies could help astronomers understand where, when and how galaxies form.

"I remember seeing this on a sky survey and saying, 'wow look at that!'" says astronomer Paul Hickson, from the University of British Columbia in Canada, in a statement. "All that I was using at the time was a big plastic ruler and a magnifying glass while looking over sky survey prints." Hickson rediscovered the galactic group in 1982 after sifting through the Atlas of Peculiar Galaxies produced by Halton Arp in 1966.  

The Hubble Space Telescope has photographed 50,000 celestial objects and captured 1.5 million snapshots. The images are stored publicly and can be viewed in the Mikulski Archive for Space Telescopes at the Space Telescope Institute in Baltimore, Maryland, or on NASA's Hubble Site.