Demo: Binary Orbit & Collision, Head-on Collision
The following movie is divided into two parts, each part showing a different
numerical simulation, with brief captions that describe
what is being shown.
Part 1: Binary black
holes orbit, lose energy because of gravitational radiation, and finally
collide, forming a single black hole; gravitational waveform, spacetime curvature, and orbital trajectories are shown. Part 2: Event horizon and apparent
horizons for the head-on collision of two black holes.
Falling Spacetime
The upper movie shows in the upper half of the screen the orbits and
the apparent horizons of the two holes, in the coordinate system
used in the computation. The bottom half of the screen shows the
spacetime geometry in the holes' orbital plane. The depth of the
surface is proportional to the scalar curvature of space. (For the
two-dimensional orbital plane the full spatial curvature is
determined by the scalar curvature.) The colors encode the lapse
function — the slowing of the rate of flow of time. The
arrows show minus the shift — which can be thought of as the
velocity of flow of space. The beginning of the inspiral is shown,
and then the last several orbits, the merger of the two holes, and
the vibrational ringdown.
The final hole does not look pefectly spherical because the computer
code that created this movie chose spatial slices with a bit of
crinkliness in them at the end. This simulation lasts for 16
inspiral orbits, followed by merger and ringdown, and it achieves a
cumulative phase accuracy for the emitted gravitational waves of
about 0.02 radians (out of roughly 200 radians, i.e. a fractional
phase error of 1 part in 10,000).
Tehnical details of the simulation on which this movie is based can
be found in a paper
by the Caltech-Cornell group. Note that slightly different
data is used in that paper; the spatial slices are chosen without
the “crinkles”.
Gravitational Waves From a Pair of Black Holes
On the right side, this movie shows the gravitational waves emitted
by a pair of black holes from large distance. The black holes
themselves are in the center of the ball, too small to be seen.
Toward the left of the ball showing gravitational waves, there is a
little grey dot. The red line on the left side shows the
gravitational wave strength which would be observed if a
gravitational wave detector would have been at that place. If you
look carefully, you'll notice that gravitational waves are emitted
in all directions, but that the waves are strongest in the "upward
direction", which is normal to the orbital plane of the holes.
This is an older movie, which stops just before the black holes
collide.
Gravitational Waves From a Pair of Black Holes
This movie shows a pair of black holes orbiting each other, giving
off gravitational waves. The movie begins with a close-up view of
the holes. We zoom out, to show some of the surrounding spacetime.
As the holes go around, they give off waves. After an initial burst
of "junk radiation" (unrealistic artifacts of the simulation), the
animation speeds up — just so it doesn't take so long —
and we see nice spiral-shaped waves. Gradually, the black holes
begin to orbit faster and faster. As they do, the waves become more
and more intense. If you watch carefully, you can see the circles
on the top and sides oscillating, just as you
would expect from a passing gravitational wave.
