Galaxies and Cosmology Seminar
Feb
23
2026
Feb
23
2026
Description
Devesh Nandal, Harvard University
From Nitrogen Enhancement to Little Red Dots: Massive and supermassive stars at cosmic dawn
Stellar evolution is now a limiting uncertainty in several high-redshift inference problems, including early chemical enrichment, the origin of intermediate and massive black holes, and the interpretation of compact red sources in JWST surveys. I will present a unified modelling effort that targets these observables with next-generation stellar evolution calculations across the massive and supermassive regimes. I will first summarise a new grid of fast-rotating Population III massive stars (7–200 Msun) evolved to the end of core oxygen burning with an extended nuclear network, which yields robust abundance predictions beyond CNO and enables remnant-mass and black hole spin estimates.
I will then present rotating supermassive stars (10^3–10^4 Msun) with self-consistent angular momentum and chemical transport evolved through advanced burning to core silicon exhaustion, and show how these models predict black hole spins consistent with current intermediate mass black hole constraints, and explain the peculiar N/O ratios in high-z galaxies. I will close by turning the models into observables. By evolving post-accretion supermassive stars to the onset of general-relativistic instability and computing their SEDs with a new pipeline, I show that SMS atmospheres can reproduce the defining spectral traits of JWST little red dots, including their red continua and strong Balmer emission. This connects the interior physics of metal free and enriched SMSs to an empirical population at cosmic dawn and ties the same evolutionary channel to direct collapse black hole seeding, little red dots, and the nitrogen-enhanced abundance patterns emerging in high redshift galaxies.
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