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Milky Weigh: scientists take weight of the galaxy

The Milky Way galaxy is lighter than previously thought, according to new research published by British-based scientists on Wednesday (July 30). 

LONDON: The Milky Way galaxy is lighter than previously thought, according to new research published by British-based scientists on Wednesday (July 30). The study led by the University of Edinburgh is the first time that scientists have been able to measure accurately the mass of the galaxy that contains our solar system, the researchers said.

The Milky Way was found to contain only half the mass of its neighbour Andromeda, which has a similar spiral structure to our own. "We always suspected that Andromeda is more massive than the Milky Way, but weighting both galaxies simultaneously proved to be extremely challenging," said Doctor Jorge Penarrubia, who led the study.

The research concluded that the extra mass of the Andromeda galaxy was down to dark matter, a little-understood invisible substance that accounts for most of the outer regions of galaxies. The scientists estimate that the Milky Way contains approximately half as much dark matter as its neighbouring galaxy, though the two are of similar dimensions.

The Milky Way and Andromeda are the two largest in a region of galaxies known to astronomers as the Local Group. Ninety per cent of the matter in both galaxies is invisible, and until now scientists have been unable to prove which is larger.

Previous research has only measured the mass of a galaxy's inner region, but the new study was able to calculate how much invisible matter is contained in outer regions.

Researchers say the findings will help them to understand how the outer regions of galaxies are structured. "Our study combined recent measurements of the relative motion between our galaxy and Andromeda with the largest catalogue of nearby galaxies ever compiled to make this possible," said Penarrubia.

The findings of the study are supported by research at the University of Cambridge, which used a different set of data to reach very similar results. The study was published in the Monthly Notices of the Royal Astronomical Society journal.

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