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Ever wonder how gravitational wave detectors like LISA would hear the signal of binary black holes orbiting around a supermassive black hole? 🔭 Well check out my first 1st author paper investigating that very topic, live on the arXiv today! 🔥📄 arxiv.org/abs/2502.10591 Explainer in 🧵👇 1/10

LISA is a space-based gravitational wave detector set to launch in the mid-2030s 📅. It is designed to capture low-frequency gravitational waves. Unlike LIGO, which detects the final merger of a compact binary, LISA would capture the evolution of the system as the objects grow closer together. ⏳ 2/10

In this paper, we considered a binary similar to GW150914 – binary black holes of ~36 and ~29 solar masses. If LISA had been observing, it would’ve detected this system years before ground detectors did! BUT, we placed the binary in orbit around a supermassive black hole of 10^8 solar masses. 👀 3/10

Stellar mass black holes in active galactic nuclei end up in circularized orbits very close to the central supermassive black hole. If two form a binary while orbiting that close, the gravitational waves emitted experience intense gravitational lensing! 🔎 4/10

The main effects that we consider on the lensing of the gravitational wave signal are: 🔹Frequency shifts from orbital motion 🔹Redshifting due to the gravitational well 🔹Magnification near the SMBH Each shaping what LISA will detect! 🌠 5/10

We ran relativistic simulations to calculate the redshift and magnification at any point in the BBH's orbit. Then, we used those results to approximate the characteristic strain and frequency – giving us a better idea of how these signals would be detected by LISA. 👂 6/10

Unlike mergers that occur in a vacuum, where the evolution of the frequency smoothly increases, here it oscillates as the binary moves towards and away from us in its orbit. 🌊 🚨 We have a problem: These oscillations prevent the signals from building up, making them hard to detect! 7/10

But there is hope! 🌟 At two points in the orbit, the rate of change of the frequency slows down and magnification is greater than zero. Causing the signal to rise above LISA’s sensitivity curve! 📈 This effect depends on the orbital radius around the SMBH and the inclination of the AGN disk. 8/10