Did massive stars blow away cosmic fog?

U. MICHIGAN (US) — High-energy light from massive stars may have cleared the dense fog that existed between galaxies in the early universe, new research suggests.

Astronomers believed that early star-forming galaxies could have provided enough of the right kind of radiation to evaporate the fog, or turn the neutral hydrogen intergalactic medium into the charged hydrogen plasma that remains today. But they couldn’t figure out how that radiation could escape a galaxy.

Researchers at the University of Michigan observed and imaged the relatively nearby NGC 5253, a dwarf starburst galaxy in the southern constellation Centaurus. Starburst galaxies, as their name implies, are undergoing a burst of intense star formation. While rare today, scientists believe they were very common in the early universe.

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Using special filters to see where and how the galaxy’s extreme ultraviolet radiation, or UV light, was interacting with nearby gas, the scientists found that the UV light is, indeed, evaporating gas in the interstellar medium. And it is doing so along a narrow cone emanating from the galaxy.

“We are not directly seeing the ultraviolet light. We are seeing its signature in the gas around the galaxy,” says Jordan Zastrow, a doctoral student, working with Sally Oey, professor of astronomy.

In starburst galaxies, a superwind from these massive stars can clear a passageway through the gas in the galaxy, allowing the radiation to escape. The shape of the cone they observed could help explain why similar processes in other galaxies have been difficult to detect.

“This feature is relatively narrow. The opening that is letting the UV light out is small, which makes this light challenging to detect. We can think of it as a lighthouse. If the lamp is pointed toward you, you can see the light. If it’s pointed away from you, you can’t see it,” Zastrow says”We believe the orientation of the galaxy is important as to whether we can detect escaping UV radiation.”

The findings, published in Astrophysical Journal Letters, could help astronomers understand how the earliest galaxies affected the universe around them.

Also contributing were researchers from the University of Maryland, the University of California, Berkeley, and Massachusetts Institute of Technology. The research is funded by the National Science Foundation. Observations were conducted with the Magellan Telescope at Las Campanas Observatory in Chile.

More news from University of Michigan: www.ns.umich.edu/