Lyman-alpha pressure clears gas from early galaxies

Researchers at the Simons Foundation's Flatiron Institute in New York and the University of Texas at Dallas report that Lyman-alpha ultraviolet radiation from clusters of young stars can expel gas and dust from early galaxies, according to EurekAlert. The study was published on November 4 in The Astrophysical Journal. eurekalert.org Images from the James Webb Space Telescope show more bright galaxies than expected in the few hundred million years after the Big Bang, and the authors propose this effect as part of the explanation. eurekalert.org

Lyman-alpha radiation and its pressure

Lyman-alpha radiation is produced when an electron collides with a hydrogen atom or when an electron joins a hydrogen ion. Gas or dust that absorbs it recoils and is pushed outward, leaving less material to form stars. eurekalert.org

The radiation behaves differently from most other light. Hydrogen atoms re-emit it almost immediately at the same wavelength, so neighboring atoms can absorb it repeatedly before it escapes. This makes radiation pressure strong, but each interaction has to be modeled, which makes direct simulation difficult. eurekalert.org

Simulation results: dense and sparse regions

Shyam Menon of the Flatiron Institute's Center for Computational Astrophysics, the lead author, and Aaron Smith of the University of Texas at Dallas did not simulate this recycling directly. They analyzed snapshots of an existing simulation of an early-universe star-forming region and calculated the force that Lyman-alpha pressure would exert on its gas and dust. eurekalert.org

In dense environments, the outward pressure was not strong enough to counteract gravity. The material recoiled but stayed bound to the stellar nursery, so the radiation likely did not strongly affect star formation there. eurekalert.org

In the lower-density spaces between stars, where gravity is weaker, the radiation prevailed. "When the density is low enough, the Lyman-alpha radiation can push the gas to really high speeds, launching explosive winds that can shoot material clear out of the galaxy," Menon said. Clearing loose gas and dust between stars opens the line of sight to them, which likely contributes to the brightness of early galaxies. eurekalert.org

Menon noted that more research is needed to understand dust in the early universe. A full picture requires simulations that self-consistently include Lyman-alpha radiation, gas flows and star formation. Olof Nebrin of Stockholm University and Smith have shown that these effects can be modeled in two dimensions. Menon hopes that improved computing power and more effective algorithms will make three-dimensional simulations possible. eurekalert.org

Flatiron Institute simulations: Lyman-alpha light blows gas out of early galaxies, making them brighter

Lyman-alpha radiation and its pressure

Simulation results: dense and sparse regions

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