November 8 Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 November 8

This image from the NASA/ESA Hubble Space Telescope shows two of the galaxies in the galactic triplet Arp 248 — also known as Wild’s Triplet — which lies around 200 million light-years from Earth in the constellation Virgo. The two large spiral galaxies visible in this image — which flank a smaller, unrelated background spiral galaxy — seem to be connected by a luminous bridge. This elongated stream of stars and interstellar dust is known as a tidal tail, and it was formed by the mutual gravitational attraction of the two foreground galaxies. This observation comes from a project which delves into two rogues’ galleries of weird and wonderful galaxies: A Catalogue Of Southern Peculiar Galaxies And Associations, compiled by astronomers Halton Arp and Barry Madore, and the Atlas of Peculiar Galaxies, compiled by Halton Arp. Each collection contains a menagerie of spectacularly peculiar galaxies, including interacting galaxies such as Arp 248, as well as one- or three-armed spiral galaxies, galaxies with shell-like structures, and a variety of other space oddities. Hubble used its Advanced Camera for Surveys to scour this menagerie of eccentric galaxies in search of promising candidates for future observations with the NASA/ESA/CSA James Webb Space Telescope, the Atacama Large Millimeter/submillimeter Array, and Hubble itself. With such a wealth of astronomical objects to study in the night sky, projects such as this, which guide future observations, are a valuable investment of observing time. As well as the scientific merits of observing these weird and wonderful galaxies, they were also — very unusually — selected as Hubble targets because of their visual appeal to the general public! [Image description: Two spiral galaxies are viewed almost face-on; they are a mix of pale blue and yellow in colour, crossed by strands of dark red dust. They lie in the upper-left and lower-right corners. A long, faint streak of pale blue joins them, extending from an arm of one galaxy and crossing the field diagonally. A small spiral galaxy, orange in colour, is visible edge-on, left of the lower galaxy.]

Galaxies: Wild’s Triplet from Hubble

Image Credit: ESA/HubbleNASADark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURAJ. Dalcanton

Explanation: How many galaxies are interacting here? This grouping of galaxies is called the Wild Triplet, not only for the discoverer, but for the number of bright galaxies that appear. It had been assumed that all three galaxies, collectively cataloged as Arp 248, are interacting, but more recent investigations reveal that only the brightest two galaxies are sparring gravitationally: the big galaxies at the top and bottom. The spiral galaxy in the middle of the featured image by the Hubble Space Telescope is actually far in the distance, as is the galaxy just below it and all of the other numerous galaxies in the field. A striking result of these giants jousting is a tremendous bridge of stars, gas, and dust that stretches between them — a bridge almost 200,000 light-years long. Light we see today from Wild’s Triplet left about 200 million years ago, when dinosaurs roamed the Earth. In perhaps a billion years or so, the two interacting galaxies will merge to form a single large spiral galaxy.