Full dark-matter jacket helped failed dwarf galaxy survive galactic collision

Researchers have said that like a bullet wrapped in a full metal jacket, a high-velocity hydrogen cloud hurtling toward the Milky Way appears to be encased in a shell of dark matter.

Astronomers believe that without this protective shell, the high-velocity cloud (HVC) known as the Smith Cloud would have disintegrated long ago when it first collided with the disk of our Galaxy.

If confirmed by further observations, a halo of dark matter could mean that the Smith Cloud is actually a failed dwarf galaxy, an object that has all the right stuff to form a true galaxy, just not enough to produce stars.

Matthew Nichols with the Sauverny Observatory in Switzerland and principal author said that the Smith Cloud is really one of a kind. It's fast, quite extensive, and close enough to study in detail.

He said that it's also a bit of a mystery; an object like this simply shouldn't survive a trip through the Milky Way, but all the evidence points to the fact that it did.

Jay Lockman, an astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, and one of the coauthors on the paper, said based on the currently predicted orbit, we show that a dark matter free cloud would be unlikely to survive this disk crossing, asserting that while a cloud with dark matter easily survives the passage and produces an object that looks like the Smith Cloud today.

The study has been published in the Monthly Notices of the Royal Astronomical Society.