Tousif
Islamতৌসিফ ইসলাম

Selected contributions

Problems I’ve tackled, methods I’ve developed, and discoveries I’ve helped make possible.

1. 01

   Mapping the hierarchy of nonlinearity in black hole dynamics

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   I developed gwTeukolsky, a modular, tiered small-mass-ratio perturbative framework for simulating binary black hole mergers, and systematically benchmarked its predictions against fully nonlinear numerical relativity simulations. I investigate how nonlinear effects emerge from perturbative dynamics and which physical corrections become important at different stages of binary evolution, from inspiral through merger. This work also introduces the Vishveshwara Catalog, the first public catalog of black-hole perturbation theory waveforms, containing 1,525 simulations across 346 binary configurations, including precessing systems.

   Vishveshwara Catalog
2. 02

   Bridging perturbation theory and numerical relativity with two scaling parameters

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   Numerical relativity (NR) accurately models comparable-mass black hole mergers but becomes computationally expensive at large mass ratios, while black-hole perturbation theory (BHPT) is formally valid in the extreme-mass-ratio limit. I demonstrated that BHPT simulations can nevertheless reproduce key features of comparable-mass mergers through a simple two-parameter rescaling of time/frequency and amplitude. This unexpected relationship, now known as the α–β scaling, provides an inexpensive bridge between two traditionally distinct regimes of black hole dynamics.

   BHPTNRSur1dq1e4Why it works
3. 03

   A universal fingerprint of eccentric black hole mergers

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   Using computationally expensive numerical relativity simulations, I demonstrated that eccentricity imprints approximately the same modulation across gravitational-wave modes and other radiative quantities. This discovery enables higher harmonics to be reconstructed from the quadrupole's eccentric modulation at a fraction of the computational cost, forming the basis of gwNRHME, a framework for extending eccentric waveform models to include higher modes. It also led to the development of a gauge-independent definition of orbital eccentricity directly from gravitational waveforms.

   PapergwModels
4. 04

   The first inference of a large black hole recoil from gravitational waves

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   Gravitational-wave observations can reveal the recoil velocities of black holes formed in mergers. Using numerical relativity surrogate models for gravitational waveforms and remnant properties, we reported the first observational evidence for a large gravitational-wave recoil, inferring a kick of approximately 1,500 km/s for GW200129. In a follow-up study, we identified another candidate, GW191109, with an inferred recoil velocity of approximately 500 km/s. These results open a new, indirect observational window onto the astrophysical environments in which black hole binaries form and the possibility of hierarchical black hole mergers.

   GW200129 recoilGW191109 recoil
5. 05

   AI agents discover interpretable analytic models of black hole mergers

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   Traditional waveform surrogates reproduce expensive numerical simulations with remarkable accuracy but often sacrifice interpretability, while first-principles analytic models struggle to describe the complete inspiral–merger–ringdown evolution. To bridge this gap, I developed gwAgent, a physics-informed, large-language-model-based agentic framework that combines known analytic limits, physical reasoning, symbolic modeling, and numerical validation to discover compact, closed-form surrogate models of binary black hole waveforms. The resulting analytic surrogates outperform conventional machine-learning approaches and traditional symbolic regression methods in the benchmarks considered, demonstrating how AI agents can contribute to interpretable scientific model discovery rather than merely automate coding. Building on this work, I also developed gwBenchmarks, a framework for stress-testing the ability of current LLM agents to carry out end-to-end scientific research tasks in gravitational-wave astronomy.

   gwAgent papergwBenchmarks paper
6. 06

   Reconstructing the origin of a runaway supermassive black hole observed by JWST and HST

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   Can general relativity reconstruct the merger history of a runaway supermassive black hole from its observed velocity alone? Recent observations with the James Webb Space Telescope (JWST) and Hubble Space Telescope (HST) have revealed evidence for RBH-1, a supermassive black hole apparently escaping its host galaxy at nearly 1,000 km/s. Using general-relativistic simulations and recoil models (gwModels) I developed, we investigated which binary black hole mergers could produce such an extraordinary kick. We found that the observed velocity alone can significantly constrain the possible progenitor binaries, favoring mass ratios between 1 and 4 and substantial black hole spins with significant precession. This work demonstrates how relativistic merger modeling can complement electromagnetic observations to uncover the otherwise inaccessible histories of supermassive black holes.

   RBH-1 papergwModels