Stream of stars in Andromeda satellite galaxy shows cosmic collision

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The Andromeda Galaxy is surrounded by a swarm of small satellite galaxies. Researchers from the Niels Bohr Institute, among others, have detected a stream of stars in one of the Andromeda Galaxy’s outer satellite galaxies, a dwarf galaxy called Andromeda II. The movement of the stars tells us that what we are observing is the remnant of a merger between two dwarf galaxies. Mergers between galaxies of such low mass has not been observed before. The results are published in the scientific journal, Nature.The galaxies in the early universe started off small and the theory of the astronomers is that the baby galaxies gradually grew larger and more massive by constantly colliding with neighbouring galaxies to form new, larger galaxies. Large, massive galaxies constantly attract smaller galaxies due to gravity and they eventually merge together and grow even larger.But not all of the small galaxies are being ‘eaten’ by the large galaxies. Some of them remain in an orbit around the large galaxy. The largest galaxy in our cosmic neighborhood is the Andromeda Galaxy, which is about 2.3 million light years away. Like our own galaxy, the Milky Way, Andromeda is a large spiral galaxy.Swarm of small galaxiesAndromeda is surrounded by a swarm of small galaxies — astronomers have counted more than 20. They have names like Andromeda I, II, III, IV…etc. …


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