Two of my papers have been published in Physical Review D!

See this visualisation of SXS:BBH:4292 that I made to celebrate! 🎉

Overall, this new paper highlights the power of using numerical relativity simulations as a tool to both validate and inform perturbative methods in the study of binary-black-hole dynamics and will lead to many exciting applications in the future!

The plot below shows that when we get into the weak-field, the post-Minkowskian calculations fall within the errors of the numerical relativity results which provides strong evidence that both approaches give the correct answer!

Next, we turn to the weak-field case where the black holes are barely interacting. We generated 9 new simulations where the black holes were further apart than ever simulated before. We then compared these results to those of the post-Minkowskian formalism.

We find that we can reliably extract up to second-order self-force effects. The plot below shows that with this information we can perfectly recover the scattering angles to within the numerical relativity errors, even at equal mass!

By fitting a simple polynomial to the scattering angle from the SpEC simulations we can extract the self-force which measures how much the small body's mass affects its own orbit. Image credit: NASA

Black-hole scattering with numerical relativity: Self-force extraction and post-Minkowskian validation The asymptotic nature of unbound binary-black-hole encounters provides a clean method for comparing different approaches for modeling the two-body problem in general relativity. In this work, we use n...

How much information can we gain by pushing numerical relativity to its limit by simulating black hole scattering encounters? My latest paper (below) explores these extreme regions of the black-hole scattering parameter space using simulations generated using the Spectral Einstein Code (SpEC).

🎉 Happy paper publication day! 🎉 Our third catalog of binary black hole simulations, now published in Classical and Quantum Gravity. And it's open access!

Scheel et al. 2025 Class. Quantum Grav. 42 195017
iopscience.iop.org/article/10.1...

Also on the @arxiv.bsky.social at arxiv.org/abs/2505.13378

We also compared our Numerical Relativity results with predictions from effective-one-body (EOB) models. In general, the models agree with the scattering angles generated with SpEC, with the plot below showing that most models differ by less than 3% in the very strong field! (6/6)

Another type of system we looked at was when the black holes have different masses. Again, we measure a difference in the scattering angle of approximately 1°. (5/6)

We also explored systems with broken symmetry. The first has black holes with spin in opposite directions. Here, for the first time, we measure the tiny difference in scattering angle of each black hole—only 0.1°! (4/6)

How do the SpEC results compare with those from other codes? The plot below shows a comparison between SpEC and the Einstein Toolkit (ETK) for a set of equal mass, non-spinning systems. Both codes agree to less than a percent! (3/6)

We simulated 60 unbound binary-black-hole encounters, covering systems with spinning black holes and mass ratios up to 10. A few examples of these trajectories are shown below. (2/6)

Highly accurate simulations of asymmetric black-hole scattering and cross validation of effective-one-body models The study of unbound binary-black-hole encounters provides a gauge-invariant approach to exploring strong-field gravitational interactions in two-body systems, which can subsequently inform waveform m...

What happens when high-velocity black holes hurtle past each other in a close encounter, deflecting through spacetime but never merging? My latest paper (below) presents the first simulations of black hole scattering generated using the Spectral Einstein Code (SpEC). (1/6)

Bonus: here's an animation I generated showing how the sausage was made. Each frame is one commit from the paper repo.

I’m incredibly proud to be part of this and to have my simulations turn into the first publicly available scattering and dynamical capture waveforms!

Below is a plot I made for the Einstein Toolkit Blue Book (arXiv:2503.12263) showing the waveforms SXS:BBH:3999 (scatter) and SXS:BBH:4000 (capture).

Happy #BlackHoleWeek! To celebrate, we’re releasing the highest-resolution ray-traced still from one of our simulations to date. This skeet has a low res preview. To zoom into the full 43,200 × 21,600 pixel rendering, head to www.black-holes.org/2025/05/07/B...
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When your work Secret Santa gift link to your research

Black holes do have mass! In fact according to the no hair theorem they are completely described by just their mass and their angular momentum.

No special analytic solutions I’m afraid. You can get approximate analytic solutions (e.g. when they’re slowly moving and far away) but nothing generic.

Yes of course!

Essentially, in Newtonian gravity when we have two bodies we know how to solve it exactly. In General Relativity, this isn’t the case as it’s too complex. One way we can find solutions is to solve the equations by putting them on a supercomputer for a month or two. That’s what I do!

For more info about my research, publications, or talks, visit my website: oliverlong.info. I’m also always happy to connect or chat!

(6/7) Outside of physics, I’m an avid climber with over 300 outdoor climbs across four countries (trad, sport, and bouldering). Here are my stats if you’re curious:

(5/7) I’m part of the effort to get the space-based Laser Interferometer Space Antenna (LISA) off the ground as an active LISA Consortium member. I’m also a former member of the LIGO collaboration.

Image courtesy of European Space Agency (ESA).

(4/7) Through my work on self-force, I became a contributor to the KerrGeodesics package of the Black Hole Perturbation Toolkit (BHPT). I am also a contributor to the Spectral Einstein Code (SpEC) of the SXS collaboration.

(3/7) In 2022, I started my postdoc at the Max Planck Institute for Gravitational Physics (AEI) in Potsdam, Germany. Here, I extended my work to include black hole scattering with comparable masses using Numerical Relativity as part of the @sxs-collaboration.bsky.social.

(2/7) I earned my MPhys in Physics from the University of Manchester (2018) and a PhD in Mathematical Sciences from the University of Southampton (2022). My PhD focused on using black hole perturbation theory to model small black holes scattering off supermassive black holes.

Artist’s impression of the horizons and curvature of a binary black hole system. Generated using Paraview.

(1/7) As I’m new here I thought I should introduce myself!

My name is Olly Long and I am a researcher working on modelling the binary black hole problem in General Relativity.

Sometimes you have to go back to the basics

Here is a visualisation of one of my Numerical Relativity simulations with @sxs-collaboration.bsky.social’s Spectral Einstein Code (SpEC).

The initially unbound system loses enough energy at closest approach to become bound leading to a merger. It’s one of the coolest looking simulations I’ve done!