Milky Way galaxy much lighter than thought

Our Milky Way weighs only a quarter to a third of the amount previously estimated, according to the latest assessment of dark matter mass of the galaxy.
It is thought the first galaxies were born as normal matter coalesced around globs of dark matter, the invisible stuff thought to make up about 80 per cent of the matter in the universe.
Alis Deason of the University of California, Santa Cruz and her colleagues compared two supercomputer simulations that mix different amounts of normal and dark matter to build the Milky Way.
One simulation created a mock Milky Way with a halo as massive as 800 billion suns. The other had a halo weighing 2 trillion suns, 'New Scientist' reported.

The team found that the smaller one was the better fit to actual observations.
"It is surprising how well it matches the most recent measurements of the properties of the halo of the galaxy," said Vasily Belokurov of the University of Cambridge, who was not involved in the work.

Galaxies grow by capturing and merging with smaller galaxies. If the Milky Way is as heavy as previously thought, it should be surrounded by thousands of satellites, but only 26 have been observed.
Most galaxies seem to have a ratio of stars to dark matter that falls within a set range, and a lighter halo means the Milky Way is breaking the rules.

"That may be pointing to the Milky Way not being the most typical galaxy for its size," said Deason.