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.
Afterward, a slower-moving yet still high-velocity cloud
of dust, debris and molten material swept over North America, ``adding more insult,'' Schultz said.
Astronomers had assumed the body was a so-called high-velocity cloud, a type of fast-moving mass of atomic hydrogen commonly found far from the galaxy.
Complex H's radio emissions show that the object is much closer than high-velocity clouds and that its motion is tied to that of the Milky Way.
The halo clouds move in tandem with the rotating Galaxy, while the high-velocity clouds
scud along much faster.
Also known as Smith's Cloud, it's one of thousands of high-velocity clouds
of hydrogen gas flying around the outskirts of our Galaxy.
Judging from models of structure formation in which small objects in the cosmos coalesce to form larger ones, "there ought to be clouds of dark matter and gas falling into our galaxy, and that's what we believe these high-velocity clouds are," he says.
The distribution of the high-velocity clouds and their speeds can best be explained, says Blitz, if the clouds are orbiting the center of mass of the Local Group.
The Andromeda finding strengthens the case that the high-velocity clouds
surrounding the Milky Way include remnant gas from the galaxy's origin, says Thilker.
The Smith Cloud is unique among high-velocity clouds
because it is so clearly interacting with and merging with the Milky Way," said Felix J.