Starlight could clear gas around bright early galaxies
Calculations suggest that ultraviolet light scattering through hydrogen could push diffuse gas away from young star clusters while leaving dense filaments feeding star formation relatively protected by gravity. This offers a possible explanation for the visibility of bright early galaxies. The peer-reviewed work applies radiation calculations to simulation snapshots, with dust abundance strongly affecting the outcome.
Science··Midday
Scattered ultraviolet light pushes gas
Peer-reviewed modelling published on 4 November explores how light-driven winds could make young galaxies more visible. The calculations concern dense star clusters in the early Universe. Lyman-alpha radiation is ultraviolet light that interacts strongly with hydrogen: repeated scattering lets photons transfer momentum to gas. The researchers calculated that pressure using snapshots from three-dimensional simulations of star formation, rather than measuring an outflow directly in an individual galaxy.[1], [2]
The question arose from images taken by the James Webb Space Telescope, which revealed more bright galaxies than expected in the first few hundred million years after the Big Bang. Shyam Menon at the Flatiron Institute, a computational research institute, and Aaron Smith at the University of Texas at Dallas investigated whether radiation around young stars could help clear obscuring material.[2]
Gravity dominates dense filaments
The modelled cloud contains dense filaments within more diffuse gas. Most stellar growth draws on those filaments, where gravity remained stronger than the calculated Lyman-alpha pressure. Lower-density regions were more susceptible to removal. That distinction could allow rapid star formation alongside routes through which young stars’ light escapes. Dust changes the balance by absorbing photons and reducing the repeated scattering that supplies the pressure.[1]
Hydrogen rapidly re-emits absorbed Lyman-alpha light at the same wavelength. Nearby atoms can then absorb it again, allowing momentum transfer to accumulate before the photon escapes. Following those interactions makes the radiation calculation demanding. The team therefore used existing star-formation snapshots to estimate the forces instead of evolving the entire radiation-recycling process alongside the gas at every step.[1], [2]
Radiation forces were added afterwards
The team compared different dust abundances and used simplified star formation models to estimate possible gas loss. Lyman-alpha forces were added after the original simulation, so the gas response to those forces was not fully fed back into the evolving system. Magnetic fields and some other stellar feedback processes were also absent. The proposed mechanism offers a route for investigating early galaxy brightness within more complete dynamical calculations.[1]
Menon identifies early dust properties as another open modelling problem. The researchers describe two-dimensional calculations coupling these effects as existing progress, while fuller three-dimensional calculations remain a goal requiring more effective methods and computational resources.[2]
