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Colossal hydrogen bridge between galaxies could be fuel line for new stars

Researchers studying a filament of hydrogen between the Andromeda and Triangulum galaxies found rotating clumps of gas the size of dwarf galaxies. But questions remain.

Image

This combined graphic shows new, high-resolution GBT imaging of recently discovered hydrogen clouds between M31 (upper r.) and M33.

Bill Saxton, NRAO/AUI/NSF

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Newly published radiotelescope observations of this segment of what researchers have dubbed the “cosmic web” reveal that about half of the neutral hydrogen gas in the bridge is contained in rotating clumps the size of dwarf galaxies. Neutral hydrogen – atoms with one proton and one electron – represents the raw material for new stars.

“If this gas is being accreted by the galaxies, then we need to understand how they're doing that. That information could, in principle, help us understand how galaxies like Andromeda, like our own Milky Way, can acquire gas to form new stars,” says Spencer Wolfe, a PhD candidate in astronomy at West Virginia University and the lead scientist on the project.

Over the past decade, astronomers have come to appreciate the potential of gas between galaxies to provide fresh fuel for making stars in spiral galaxies.

Star formation in the universe appears to have peaked some 10 billion to 11 billion years ago. Stellar birthrates these days are less than 10 percent of what they were then, notes Robert Braun, an astronomer at the Australia Telescope National Facility in Epping, New South Wales.

Left to their own devices, galaxies have on average about 1 billion to 2 billion years worth of gas in the cosmic tank, a condition that has existed throughout most of the universe's history, Dr. Braun writes in an e-mail. Many of them, therefore, should have stopped forming stars billions of years ago. Moreover, the total mass of stars in the universe today is about five times higher than the amount of neutral hydrogen available 12 billion years ago, suggesting that the universe's larger inventory of ionized hydrogen kept star formation going in some way.

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