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It sounds impossible to discover a dwarf galaxy at a distance of 10 billion light years, given that such galaxies are difficult to detect even when in orbit around the Milky Way, but this is just what is being claimed by Simona Vegetti and colleagues at the Massachusetts Institute of Technology.
The team was working with the Keck II telescope in Hawaii observing a gigantic elliptical galaxy (called JVAS B1938+666 and located at a distance of 9.8 billion light years) that acts as a gravitational lens for an even more distant galaxy.
The Einstein ring around this galaxy (photo) is formed by the bending of light rays by the gravitational field of the massive elliptical galaxy. In this case the ring is especially bright in one region.
By using complex mathematical models to determine the mass distribution of the lens, Vegetti and colleagues noted that this bright region within the Einstein ring was best explained by the presence of a dwarf satellite galaxy around the massive elliptical, JVAS B1938+666.
The presence of a dwarf satellite galaxy has therefore been inferred at a distance where its direct detection would be completely impossible. The shape of the rings and arcs around gravitational lenses can therefore be used to infer the presence of satellite galaxies.
In principle then, it is possible to detect very distant dwarf galaxies even if they are made up almost exclusively of dark matter, which, according to some researchers, could be the most common type of galaxy in the Universe, so much so that our own Galaxy may be surrounded by 10,000 such objects, yet to be discovered!
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by Michele Ferrara & Marcel
Clemens |
credit: D. Lagattuta / W. M. Keck Observatory |
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