Study reveals importance of hydrogen atoms for star formation

"We cannot neglect atomic hydrogen even in galaxies that contain tens of billions of solar masses of molecular hydrogen," said astrophysicist Barbara Catinella.
By Brooks Hays   |   Oct. 10, 2017 at 3:14 PM
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Oct. 10 (UPI) -- Until recently, astronomers assumed hydrogen molecules fueled star formation in young galaxies. But new research suggests atomic hydrogen may be equally important to star formation.

In the local universe, most hydrogen found inside galaxies exists as individual atoms. Scientists assumed younger galaxies would host less atomic hydrogen and more molecular hydrogen. But cosmic surveys suggest even the earliest galaxies were rich in atomic hydrogen.

Now, new analysis by researchers at the University of Western Australia and the International Center for Radio Astronomy Research confirms even galaxies featuring intense rates of star formation host large amounts of atomic hydrogen.

Previous studies of "cosmic noon" galaxies have revealed massive reservoirs of molecular hydrogen. Cosmic noon describes the universe's apex of star formation during a period roughly seven billion years after the Big Bang.

Until now, most astronomers assumed there was little room left for atomic hydrogen in these star-filled galaxies. However, scientists had no way to confirm their suspicions. The most powerful telescopes still can't detect individual gas atoms at such great distances.

Astronomers can detect individual atoms at more intimate distances. During the most recent survey, scientists discovered galaxies three million years younger than the Milky Way with molecular gas reservoirs as large as those belonging to cosmic noon galaxies.

The newly surveyed galaxies are much closer, which allowed astronomers to locate individual hydrogen atoms using the world's largest radio telescopes, Puerto Rico's Arecibo Observatory and the European Southern Observatory's Atacama Large Millimeter/submillimeter Array in Chile.

"What we found is that despite hosting 10 billion solar masses of molecular gas these young galaxies turn out to be very, very rich in atomic hydrogen as well," Luca Cortese, an astrophysicist with ICRAR, said in a news release. "The balance between atomic and molecular hydrogen is pretty much the same as in the Milky Way. In other words, it's still dominated by atomic gas."

The findings -- detailed this week in the journal Astrophysical Letters -- suggest atomic hydrogen plays a significant role in star formation.

"It shows that we cannot neglect atomic hydrogen even in galaxies that contain tens of billions of solar masses of molecular hydrogen," said ICRAR astrophysicist Barbara Catinella.

Researchers hope newer, more powerful radio telescopes will shed further light on the roles atomic and molecular hydrogen play in start-forming regions.

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