high-velocity clouds

high-velocity clouds

Small molecular and diffuse clouds, often far from the galactic plane, that have radial velocities differing significantly – sometimes up to 100 km s–1 – from those predicted by a simple Galactic rotation curve. Some may be associated with tidal effects, such as the Magellanic Stream (see Magellanic Cloud), while others are more likely due to galactic fountains.
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Instead, astronomers suspect that some of them were created by high-velocity clouds (HVC).
Most high-velocity clouds share a common origin with the Milky Way, either as the leftover building blocks of galaxy formation or as clumps of material launched by supernovas in the disk of the Galaxy.
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.
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.
The halo clouds move in tandem with the rotating Galaxy, while the high-velocity clouds scud along much faster.
Accurate distances are known for only a handful of high-velocity clouds.
Despite the Green Bank observations, mysteries remain about the origin of high-velocity clouds.
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.
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.
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 origin of these so-called high-velocity clouds had been uncertain since they were first detected by Dutch astronomer Jan Oort in 1961.

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