Full List Of Publications

Building the seed models I: Seed formation dense and metal-poor gas

In this paper, we present the first set of black hole seed models built using zoom-in cosmological simulations. These simulations explore seed formation within dense, metal-poor gas and demonstrate that the characteristics of these seeding environments can be inferred from gravitational wave event rates detectable by LISA.

Building the seed models II: Seed formation in under low gas spins and high UV radiation

In this paper, we introduce a new set of seed models for representing Direct Collapse Black Holes (DCBHs). In addition to requiring dense and metal-poor gas, these models place seeds exclusively in regions exposed to sufficiently high ultraviolet (UV) radiation and characterized by low gas angular momentum. We find that these criteria are highly restrictive, indicating that the canonical conditions for DCBH formation are exceedingly rare in cosmological environments.

Build the seed models III: Representing low mass seeds in large cosmological simulations— A new stochastic seed model

In this paper, we develop a novel stochastic seed model capable of representing black hole seeds with masses 10–100 times below the resolution limit of large-volume uniform cosmological simulations.

Simulations of low mass black hole seeds in large cosmological volumes

In this paper, we introduced the first set of uniform-volume simulations from the BRAHMA suite. A unique feature of these simulations is their multi-scale design, comprising several simulation boxes with successively increasing volumes and correspondingly decreasing resolutions. Only the smallest, highest-resolution box is capable of resolving our target seed black hole mass of ∼1000 solar masses, which forms in dense, metal-poor gas regions. In the larger, lower-resolution boxes—where such conditions cannot be directly resolved—seed black holes are stochastically placed using a prescription that is calibrated against the high-resolution results, thereby allowing consistent seeding across all volumes. The simulations predict strict upper limits for black hole merger rates that range from ~200-2000 mergers per year depending on the seed model.

Assembly of high-z JWST black hole populations and implications on heavy seed formation

This project explores how the population of black holes detected by JWST can inform our understanding of heavy black hole seed formation in the early Universe. Using a new set of cosmological simulations from the BRAHMA suite, we model the birth of heavy seeds based on key physical conditions—including gas density, metallicity, angular momentum, Lyman-Werner radiation, and the halo environment. Each simulation explores different assumptions about how efficiently these seeds form. Our results show that to explain the most massive black holes observed at high redshift, we need a much higher abundance of heavy seeds than predicted by standard direct-collapse models. Moreover, these seeds must merge rapidly—within about 750 million years—to reach the extreme black hole masses seen at cosmic dawn.

Probing the assembly of z > 6 luminous quasars using constrained simulations

Using high-resolution simulations of a rare, compact halo in the early Universe, we explored how supermassive black holes powering quasars at z>6 might grow under different black hole seeding models. We find that in the earliest epochs (z>9), black hole growth is driven primarily by mergers, with gas accretion playing a minor role. By z∼6, however, gas accretion becomes the dominant contributor to black hole mass growth. Our results suggest two possible pathways to forming these early quasars: one in which abundant heavy seeds undergo frequent mergers at early times to boost growth before accretion takes over, and another in which more efficient gas accretion—through reduced feedback or super-Eddington rates—can drive rapid black hole growth with fewer initial seeds.

Local signatures of black hole seeding

We explore how different black hole seeding models leave behind signatures in today’s Universe using BRAHMA cosmological simulations run to z=0. By comparing several seed formation scenarios, we find that lowest mass black holes (~1e5-1e6 solar masses) living in dwarf galaxies retain strong imprints of their early origins. These black holes assembled their mass mostly via mergers rather than gas accretion. The signatures of seeding get erased for > 1e7 solar mass black holes, wherein gas accretion dominates the black hole mass assembly. Our results suggest that observations of black holes in local dwarf galaxies could help distinguish between competing models of seed formation in the early Universe.

Local signatures of black hole seeding on the evolution of the M∙−σ relation

Using the BRAHMA simulations, we investigate how different black hole seeding models affect the evolution of the black hole–velocity dispersion (M∙−σ) relation across cosmic time. We find that while lenient seed models maintain a stable M∙−σ relation over redshift, more restrictive models show lower normalization at early times and gradually evolve toward the local relation. These trends reflect merger-driven growth in low-mass galaxies and accretion-driven growth in high-mass galaxies. Additionally, the scatter in the M∙−σ relation increases for more restrictive seed models, driven by black holes that fail to grow beyond their initial seed mass. These results offer new pathways to constrain black hole seeding using both high- and low-redshift galaxy–black hole scaling relations.

Dynamics of low mass black hole seeds in the early Universe

We use cosmological simulations from the BRAHMA suite to study how low-mass black hole seeds move, merge, and grow in the early Universe (z≳5). By modeling dynamical friction, we find that many (but not all) black holes are able to sink to the galaxy centers and merge with other black holes. These mergers dominate black hole assembly at early times, with gas accretion playing a minimal role. Our results predict hundreds to thousands of black hole mergers per year at high redshift—offering key targets for future gravitational wave observatories like LISA.