Astronomers identify intergalactic gas station on the outskirts of the Milky Way

Our Galaxy may have been consuming clouds of gas in a magnetic wrapper to keep making stars for the past eight billion years.

That’s the conclusion of astronomers at CSIRO, Australia's national science agency.

Dr Alex Hill, the lead author of a study of the Smith Hydrogen Gas
Cloud, a large gas cloud falling into the our Galaxy from intergalactic space, explained:

“Clouds like this may provide the fuel for our Galaxy to make stars, but they must be held together by something, or they’d disintegrate when they hit the warm outer part of the Galaxy — the halo. They wouldn’t reach the Galaxy’s disk, where the star-making is going on.”

The investigators found that the Smith Cloud has a magnetic field. It’s 50 000 times weaker than the Earth’s, “but it’s probably still strong enough to keep the cloud together”, Dr Hill said.

The findings were published recently in The Astrophysical Journal.

“This is one of the few such clouds large enough for us to be able measure its magnetic field,” added Dr Naomi McClure-Griffiths, a member of the research team.

“It seems the cloud is protected by a magnetic bubble, the same way the Earth’s magnetic field protects it from the solar wind.”

Named after its discoverer, Gail Bieger (née Smith), the Smith Cloud is at least two million times the mass of our Sun. If it were visible to the naked eye, it would look 20 times wider than the full Moon.

The Smith Cloud is one of thousands of “high velocity clouds” of hydrogen gas flying around the outskirts of the Milky Way. Astronomers believe their origins are mixed, some stemming from burst “bubbles” in the gas of our Galaxy, some being primordial gas, and some associated with small galaxies our Galaxy’s gravity is shredding from a distance.

The Smith Cloud is probably either semi-primordial gas condensing from the halo of the Milky Way or gas stripped from another galaxy.

Traveling at around 80 miles a second (130 kilometers a second), the Smith Cloud is only 8 000 light-years from our Galaxy’s disk and will drive into it in less than 30 million years.Its impact should produce galactic fireworks of some sort – possibly a burst of star formation or a supershell of neutral hydrogen.

Related links:

An all-sky map of high-velocity clouds

Astronomy Picture of the Day: High Velocity Clouds and the Milky Wa