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!

GW200129

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!

Credits

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.