The image above might remind us of abstract expressionism or an action painting by Jackson Pollock, but it is actually the latest observation of a group of galaxies known as Stephan’s Quintet. While the group visually consists of five galaxies, only four are actually close to each other, making it an incredible four-way merger. Astronomers have used the extremely rare group to better understand the complex dynamic of galactic collisions.
The new image was obtained by the Canada-France-Hawaii Telescope, located near the top of Mauna Kea, Hawaii. The international team used the telescope's capability of making deep visible observations to look for structures with low surface brightness (LSB) that might have been missed by previous observations. And the search paid off.
The astronomers observed several LSB features stretching across the galaxies. Some structures were completely or partly visible in previous observations of the group. Some were completely new. The latter category includes the discovery of a diffuse, reddish halo of stars around NGC 7317, an elliptical galaxy that's part of the Quintet.
The group has been used to understand star-formation episodes during mergers and the production of tails of gas and stars, as well as related phenomena like gas ramming and the formation of intergalactic systems. The reddish halo has implications for all of these. It suggests that the interaction has been going on for a long time, so the stellar population in these tidal structures has aged and become redder. These findings are reported in the Monthly Notices of the Royal Astronomical Society.
The brightest member of the group is NGC 7320, the unconnected galaxy, which is actually located 39 million light-years away, closer than the 340 to 210 million light-years for the rest of the galaxies. This galaxy is currently going through an intense star-formation phase.
The observations were done on a wide field of view and allowed for the analysis of other objects unrelated to the Quintet. The telescope captured diffuse filaments surrounding NGC 7331, another foreground spiral galaxy visible in the full image below. The researchers also noticed that the image is contaminated by infrared emissions from the galactic cirrus, cloud-like structures that are located around the disk of the Milky Way
Stephan’s Quintet was the first compact group ever discovered, observed for the first time in 1877 by French astronomer Édouard Stephan from whom it takes its name.