Extremely long star stream in Berenice's hair
A star stream ten times the length of our galaxy was discovered in the constellation "Hair of Berenice". It stretches between the world islands of the Coma galaxy cluster.
Around 300 million light years away from us, in the rather inconspicuous constellation "Hair of Berenice" (Latin: Coma Berenices), a long stream of stars stretches between the members of the Coma galaxy cluster. It is around 1.7 million light years long, which is about ten times the size of our galaxy. This makes it the longest known stellar stream of all. Significantly smaller stellar streams are known in the vicinity of our Milky Way system and around nearby galaxies, but never before has such an extensive structure been detected at such a great distance.
Star streams are formed when dwarf galaxies merge with much larger islands. Tidal interactions between the galaxies cause the smaller world island to be pulled apart and its stars to arrange themselves in elongated streams. Over many millions of years, the members of these formations merge with the stars of the large galaxy and become part of it.
However, no associated galaxies can be recognised in the star stream that has now been discovered, which could have been responsible for its formation. It simply appears to be drifting between the galaxies of the cluster. The group led by Javier Román from the Dutch University of Groningen christened it the "Giant Coma Stream" and published it in the journal "Astronomy & Astrophysics". Its existence is not so easy to explain, because such a stellar stream is a fragile structure. It is exposed to the gravitational fields of the various members of the Coma galaxy cluster and should be dissolved relatively quickly by their tidal interactions.
The team hopes to discover more such stellar streams in the data from the recently commissioned space telescope Euclid in order to learn more about their distribution and possible formation pathways.
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Cover image: © William Herschel Telescope/Román, J. et al: A giant thin stellar stream in the Coma Galaxy Cluster. A&A 679, 2023, fig. 1 / CC BY 4.0 (detail) Ten times longer than the width of our Milky Way system, a stellar stream extends in the constellation «Hair of Berenice».
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