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Phil Lynch @physlynch.bsky.social · 08/08/2026

I just released my first python package on PyP! If you ever wanted to perform Chebyshev interpolation in multiple dimensions then you should use ChebyshevND 🧪 ⚛️ 🧮 pypi.org/project/Cheb...

Two python plots. The one on the right shows a continuous function f(x), the Chebyshev nodes it is sampled on and the smooth interpolant. The left plot shows the absolute difference between the original function and the interpolant which is on the order of 10 to the power of negative 9.

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Phil Lynch @physlynch.bsky.social · 12/09/2025

Future space missions like LISA will listen to gravitational waves from some of the most extreme events in the universe: Extreme Mass-Ratio Inspirals (EMRIs). These are systems where a stellar mass black hole spirals into a supermassive one while emitting low frequency graviational waves

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Phil Lynch @physlynch.bsky.social · 12/09/2025

New paper on the arXiv today about systematic errors when modelling the gravitation waveform from extreme mass ratio inspirals and their impact on LISA data science Huge thanks to my collaborators, especially Hassan Khalvati, for getting this project over the line! 🧪⚛️🔭🧮 arxiv.org/abs/2509.08875

A posting on the arXiv preprint server.

Title: Systematic errors in fast relativistic waveforms for Extreme Mass Ratio Inspirals

Authors: Hassan Khalvati, Philip Lynch, Ollie Burke, Lorenzo Speri, Maarten van de Meent, Zachary Nasipak

Abstract: Accurate modeling of Extreme Mass-Ratio Inspirals (EMRIs) is essential for extracting reliable information from future space-based gravitational wave observatories. Fast waveform generation frameworks adopt an offline/online architecture, where expensive relativistic computations (e.g. self-force and black hole perturbation theory) are performed offline, and waveforms are generated rapidly online via interpolation across a multidimensional parameter space. In this work, we investigate potential sources of error that result in systematic bias in these relativistic waveform models, focusing on radiation-reaction fluxes. Two key sources of systematics are identified: (i) the intrinsic inaccuracy of the flux data, for which we focus on the truncation of the multipolar mode sum, and (ii) interpolation errors from transitioning to the online stage. We quantify the impact of mode-sum truncation and analyze interpolation errors by using various grid structures and interpolation schemes. For circular orbits in Kerr spacetime with spins larger than a≥0.9, we find that ℓmax≥30 is required for the necessary accuracy. We also develop an efficient Chebyshev interpolation scheme, achieving the desired accuracy level with significantly fewer grid points compared to spline-based methods. For circular orbits in Kerr spacetimes, we demonstrate via Bayesian studies that interpolating the flux to a maximum global relative error that is equal to the small mass ratio is sufficient for parameter estimation purposes. For 4-year long quasi-circular EMRI signals with SNRs=O(100) and mass-ratios 10^−4−10^−6, a global relative error of 10−6 yields mismatches <10^−3 and negligible parameter estimation biases.

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Phil Lynch @physlynch.bsky.social · 01/12/2024

That's right. Current ground based detectors (LIGO-Virgo-Kagra) are sensitive to the higher frequency part of stellar mass black hole mergers, which consist of the late inspiral, merger and ringdown. We need spaced based detectors like LISA to see lower frequency signals like EMRIs

A diagram showing the gravitational waveform of a black hole binary merger, separated into the inspiral, merger and ringdown stages.

Image credit: M. Favata/SXS/K. Thorne

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Phil Lynch @physlynch.bsky.social · 30/11/2024

But we'll be able to measure these signals with the upcoming European Space Agency's LISA mission. If we can model these signals accurately, we can learn a lot about supermassive black holes and their environments and put Einstein's Theory of General Relativity through it's toughest test yet

An artistic representation of the European Space Agency's (ESA) Laster Interferometer Space Antenna (LISA). The image shows the triangular LISA constellation of satellites connected via laser beams as it lags behind the earth in its solar system orbit. In the distance, there is an active galaxy from which ripples in the fabric of spacetime are emanating.

Image Credit: University of Florida / Simon Barke (CC BY 4.0)

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Phil Lynch @physlynch.bsky.social · 30/11/2024

I model the gravitational waves that come from binary black holes where one is a supermassive black hole and the other is a much smaller (but still pretty huge) stellar mass black hole, known as Extreme Mass Ratio Inspirals. As you can see, these things get pretty complicated 🧪⚛️🎢🔭🧮

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Phil Lynch @physlynch.bsky.social · 14/11/2024

Last week, Ollie Burke and I put out a note describing how to convert between all the different orbital phases used to describe orbits around a spinning black hole. The most fun reason to do this is. to help make visualisations like this one arxiv.org/abs/2411.04955

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