Milky Way Clouds: Mysterious, Fast-Moving Hydrogen Clouds Racing Through the Galaxy Discovered

12_5_Hubble Gas Cloud
The 25th anniversary of the Hubble Telescope was marked by this image featuring a giant hydrogen cloud in the Milky Way. NASA/ESA/Hubble Heritage Team (STScI/AURA)/A. Nota (ESA/STScI)/Westerlund 2 Science Team

Mysterious, rapid-moving clouds have been charted in never-before-seen detail on a map of the entire sky. These strange, high-velocity gas clouds are moving at odds with the usual rotation of the Milky Way.

Australian astronomer Tobias Westmeier, from the International Centre for Radio Astronomy Research, used a high-resolution image of the sky to produce the most sensitive map of high-velocity clouds ever—the "all-sky map."

Using the map, he was able to highlight the high-velocity clouds, which are moving at different speeds to the Milky Way. His results are published in Monthly Notices of the Royal Astronomical Society.

"These gas clouds are moving towards or away from us at speeds of up to a few hundred kilometers per second," he said in a press release. "They are clearly separate objects."

Vast, mysterious clouds

These strange clouds are enormous, covering up to 13 percent of the sky. Westmeier's map reveals the texture and shape of clouds in minute detail, exposing subtle filaments, branches and clumps which were previously invisible.

The map visualizes high-velocity hydrogen clouds using data from the HI4PI survey. ICRAR

"It's something that wasn't really visible in the past, and it could provide new clues about the origin of these clouds and the physical conditions within them," he said.

Further still, Westmeier used the map to discover the extragalactic source of some of the clouds. "We know for certain the origin of one of the long trails of gas, known as the Magellanic Stream, because it seems to be connected to the Large and Small Magellanic Clouds," he said. "But all the rest, the origin is unknown."

The Large and Small Magellanic Clouds are dwarf galaxies that orbit the Milky Way

The Milky Way pictured edge-on. Gaba p/WikiMedia Commons

The newly discovered clouds are very close—within about 30,000 light years—to the "disk" of the Milky Way. The disk is a way of visualizing objects like planets within the galaxy. As you can see in the image above, the disk is surrounded by a "galactic halo." Westmeier argues that the closeness of the clouds can help us decipher their origin.

"It's likely to either be gas that is falling into the Milky Way or outflows from the Milky Way itself," he said. "For example, if there is star formation or a supernova explosion it could push gas high above the disc."

Westmeier has made the map freely available online to support "the entire community" of astronomers. If you think you might be able to crack the mystery of these massive gas clouds, you can take a look here.