Stellar feedback on the largest & smallest scales: From the first star-forming halos, to the first self-consistent multidimensional simulations of Lyman-α feedback

by Olof Petter Nils Axel Nebrin (Stockholm University)

Wednesday 3 Jun 2026, 14:00 → 15:00 Europe/Stockholm

Albano 3: 4205 - SU Conference Room (40 seats) (Albano Building 3)

Observations of the high-redshift Universe, and local faint and ancient fossils from that epoch, reveal that star formation at Cosmic Dawn could be both efficient and highly inefficient. Stellar feedback from massive stars is thought to shape the fate of star-forming clouds, launch galactic winds, and regulate star cluster formation. A key goal of simulations is to reproduce the observed diversity of objects and star formation efficiencies from first principles, which demands careful studies of the stellar feedback processes at play.

In this seminar, I will present the main results of my PhD project on star and galaxy formation at Cosmic Dawn. I will begin by giving a brief overview of my work on when and where the first stars and galaxies formed. I will show how large-scale reionization turned the Universe hostile to star formation in the smallest dark matter halos.

Next, I will focus on what happens on smaller scales when star formation commences. What feedback processes are at play? It has long been suspected that radiation pressure from scattering Lyman-α (Lyα) photons could exert a dominant force in dust-poor environments. Despite this, multidimensional, self-consistent Lyα radiation hydrodynamics simulations have been computationally infeasible. I will present the first such simulations, using a novel code called LYDION.

With LYDION, we simulate the feedback around massive stars in dust-poor clouds and find that Lyα radiation pressure dominates over all other feedback channels in these environments, launching significantly stronger outflows. As a result, most current galaxy and star formation simulations may be missing the strongest feedback process at play in young dust-poor star-forming regions at Cosmic Dawn, complicating comparisons against observations from JWST.