The Hubble Space Telescope received a very spectacular image of a group of colliding galaxies known under the designation Arp-Madore 2339-661. It may seem that only two galaxies are involved in it. However, a detailed analysis revealed a hidden participant in this cataclysm.
The Arp-Madore 2339-661 group is located at a distance of about 500 million light-years from Earth in the direction of the constellation Tucana. The Hubble image clearly shows two clearly defined galaxies: NGC 7733 (smaller, bottom right) and NGC 7734 (large, top left).
Both objects are classified as spiral galaxies with a bar. Each of them has a brightly glowing center, and their spiral arms are strewn with numerous young star clusters. This indicates that the compaction of gas clouds caused by the gravitational interaction has already started the processes of active star formation. In addition, both galaxies are connected by a bridge consisting of ejected stars, gas and dust.
But where is the third galaxy? It can be seen if you look closely at the upper spiral arm of NGC 7733, where there is a visually noticeable knotty structure that differs in color and is hidden by dark dust. It could easily be mistaken for part of NGC 7733, but velocity and direction analysis show that this node has a significant additional redshift. This means that it is most likely an independent entity, and not part of NGC 7733.
This case clearly demonstrates one of the problems that researchers often face: finding out whether we are really facing one astronomical object or several. As for the Arp-Madore 2339-661 group, its participants will continue their interaction and merge into a single object in the future.
According to https://esahubble.org
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