GW200129 is a gravitational wave signal observed by the detectors LIGO and Virgo, emanating from the merger of two black holes. This was the first black hole merger identified as having a large recoil velocity for the final black hole left behind after the merger. We provide some visualizations of this binary and its properties in this webpage. For more details, please refer to our paper arXiv:2201.01302.


You can download these movies by right-clicking on them. On Chrome choose "Save Video As..", and similar for other browsers. These are free to use, but please credit us!


Visualization of the binary black hole merger GW200129, generated using the binary black hole explorer. The binary parameters are chosen to be the maximum likelihood values from our paper arXiv:2201.01302, in particular, mass ratio q=2.1, total mass M=74.5 solar masses, and dimensionless spins chi1=[-0.46, 0.80, 0.21] and chi2=[0.01, -0.41, -0.55]. As there is substantial spin in the orbital plane, the binary precesses, which modulates the gravitational wave signal, and leads to a large kick. See the binary black hole explorer for further details on this movie.

The final black hole has a kick vector = [422, -1071, -1832] km/s, and a kick magnitude of 2164 km/s. This velocity is greater than the escape of velocity of most known galaxies, and the final black hole would simply get ejected! However, keep in mind that this is only at the maximum likelihood point. For the full kick posterior see below, and our paper arXiv:2201.01302 for more quantitative staments.

Kick posterior for GW200129

Posterior samples for the full kick vector for GW200129. Each purple marker indicates a kick posterior sample; an arrow drawn from the origin to the marker would show the kick vector. The outer radius of the sphere corresponds to a kick magnitude of 2500 km/s. The x-axis (orange) and y-axis (green) are shown as arrows near the origin; the x-y plane is orthogonal to the orbital angular momentum direction. The blue markers on the sphere show posterior samples for the line-of-sight direction to the observer. For both distributions, the color reflects posterior probability density. See our paper arXiv:2201.01302 for more details.

Spin posterior for GW200129

Similar to above, but now showing the posterior samples for the dimensionless spin vectors for GW200129. The outer radii of the spheres correspond to the maximum spin magnitude of 1. Notice that the spin of the heavier black hole is large and lies nearly in the orbital plane; this leads to precession. The spin of the lighter black hole is not well measured, and the spin posterior is driven by the prior itself. See our paper arXiv:2201.01302 for more details.

Spin posterior vs time

Similar to above, but now showing the spin posterior at different times before the merger (t=0), and we now show the heavier black hole on the right (for a technical reason). At each time, the posterior represents the spins measured at that point in the evolution of the binary; becuase spins change for precessing binaries, the measured spins also change. Even though the spins evolve deterministically, and one can evolve the early time posterior to get the late time posterior, how well the spins are constrained depends on where they are measured. In particular, in the bottom video you can see that the in-plane spin angle for the primary black hole is much better constrained near the merger. See our earlier paper arXiv:2107.096922 for more details of how this works, including details of the frame in which these spins are measured.

GW200129 (short version)

Same as above, but only showing the last 20 seconds.

Hearing the waves

Linear polarization

Circular polarization

The gravitational-wave frequencies that LIGO-Virgo detect are already in the range that human ears can hear, from around 20 Hz — 20kHz. This lets us “sonify” GW signals, and the characteristic of the inspiral of two black holes or neutron stars is a “chirp” that starts quietly at low frequencies, and sweeps up in frequency while getting louder. For a pair of neutron stars, this can last around 100 seconds, but for a pair of heavy black holes like GW200129, it lasts less than a second. In real time, this would be very short and hard to hear. Instead, we stretch the signal out over around 30 seconds so you can appreciate the chirp and any details, like modulation due to precession of orbital plane.

When stretched out this long, the frequencies would be “infrasound”—too low frequency for humans to hear. Instead, we cheat by multiplying all the frequencies back up into the audible band. Just like light, GWs carry two polarizations, and also like light, we can either work with linear polarizations (“plus” and “cross”) or circular polarizations (“left” and “right”). The first sonification above is in the linear basis, and the second is in the circular basis.

If we see an inspiral from exactly face-on (looking into the orbital plane), its signal would be dominated by right-circularly-polarized waves. If exactly face-off, it would be dominated by left-circularly-polarized. And if it’s edge-on, the signal would be dominated by the “plus” linear polarization. Be sure to use headphones, and see if you can hear the orientation of the binary!


These visualizations on this page were created by Vijay Varma and Max Isi for the paper arXiv:2201.01302. The sound files were created by Leo Stein. Please credit us, and cite our paper, if you use these materials in your work, talks or outreach.