About 300 million light-years away from us, in the rather inconspicuous constellation Coma Berenices, a long stream of stars stretches between members of the Coma galaxy group. It is about 1.7 million light-years long, about ten times the size of our galaxy. This makes it the longest stellar stream ever known. Much smaller stellar streams are known in the vicinity of the Milky Way system and around nearby galaxies, but such an extensive structure has never been detected before at such a great distance.
Star streams form when dwarf galaxies merge with larger island worlds. Tidal interactions between galaxies break up the smaller island world and arrange its stars into long streams. Over millions of years, members of these structures unite with and become part of the stars of the larger galaxy.
However, the now discovered stellar stream does not reveal any associated galaxies that could be responsible for its formation. It simply appears to float among the cluster’s galaxies. The group led by Javier Roman of the University of Groningen in the Netherlands named it the “Giant Coma Stream” and published it. In the specialized journal “Astronomy and Astrophysics”. Its existence is not easy to explain, because such a stream of stars is a fragile structure. It is exposed to the gravitational fields of various members of the Coma galaxy group and should dissipate relatively quickly through tidal interactions.
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