An international group of astronomers discovered tidal fragments in the Galactic group NGC 7232. The gigantic structure consists of cold neutral atomic hydrogen (HI) and extends about 450 thousand light years. This is reported in an article published in the repository of preprints ARXIV.ORG.
In the course of observation of the NGC 7232 group, consisting of at least 19 galaxies and located at a distance of 78 million light years (in relative proximity from the Milky Way), scientists used Meerkat radio telescope in South Africa. It turned out that the galaxies in the group actively interact with each other, which is expressed in various structures, such as tidal tails, bridges and other formations of stars and interstellar substances. They arise when tidal forces deform each galaxy, as a result of which tails are discarded, where stars continue to form.
In particular, astronomers revealed extended debris from cold neutral atomic hydrogen, located around the core of a triplet galaxy, known as NGC 7232/3 (consists of three spiral galaxies: NGC 7232, NGC 7232B and NGC 7233). The streams of the substance extend on 20 angular minutes, which corresponds to 456 thousand light years, which is about three times the length of the region of neutral atomic hydrogen in the troika galaxies.
Tidal debris contain HI with a total mass of 4.5 billion solar masses. These are more than half of the total mass of hydrogen, located in NGC 7232/3. NGC 7232/3, NGC 7233 and NGC 7232 lost a significant amount of HI, while NGC 7232B seems to be characterized by an excess of gas. However, scientists noted that, in general, the NGC 7232/3 triplet does not suffer from the deficit of atomic hydrogen, participating in star formation, despite tidal effects.