No sound is produced when two black holes collide. Still, if you listen carefully, you can hear this.
[CLIP: Black hole “chirp”]
Let’s hear it again.
[CLIP: Black hole “chirp”]
That “chuck” is the sound heard from two black holes colliding at a distance of about a billion light-years from Earth. The sound rises as they approach the spiral and stops abruptly when they join.
However, sound cannot travel through a vacuum space. So what exactly are we hearing?
Each of these black holes weighs as much as a few stars. It’s heavy enough that it creates waves, especially gravitational waves, as it passes through space.
These waves are undulations of the fabric of spacetime that fan outward at the speed of light, like ripples in a cosmic pond.
Albert Einstein predicted this phenomenon in 1916 based on general relativity, but was skeptical that gravitational waves could be detected.
Even strong ripples from colliding black holes produce ripples about 1/1000th the size of a proton.
It took scientists almost a century to prove him wrong.
They are now building and expanding a global network of observatories, and have detected gravitational waves from about 100 cosmic collisions so far.
When recorded, analyzed, and translated into sound, each space-time clash becomes its own signature, data-rich chirping.
Let’s listen again:
[CLIP: Black hole “chirp”]
This long, low accumulation is a sign of a slower, more subdued merger from a relatively lightweight spiral black hole.
A more abrupt cry, such as: [CLIP: Black hole “chirp”]
This is a sign that the merger of more massive black holes is accelerating…
In this case, the two combine to form a mass over 80 times the mass of the Sun.
Now, after a long hiatus for upgrades and the COVID-19 pandemic, the world’s gravitational-wave observatories are re-tuning to this celestial symphony.
Gravitational wave observatories do not have mirrors or lenses like regular telescopes.
Instead, they laser a long tunnel and place two arms flat on the ground in an L-shape.
Lasers reflected between mirrors at the end of each arm act like violin strings, producing slightly different frequencies as their path through space is stretched and compressed by passing gravitational waves. .
Shortening the laser will give you a higher pitch, similar to a violin string. The longer it is, the lower the pitch. Converting all this laser vibrato into sound, you can even hear a black hole collide with a “chirp”.
Scientists have built dozens of these laser-based ears around the world to listen for gravitational waves from cosmic sources.
One, called LIGO, has two detectors, one in Hanford, Washington, and one in Livingston, Louisiana.
There is also the VIRGO observatory near Pisa, Italy and the KAGRA detector in Hida, Japan.
Another detector will be built in India.
A cross-check between these stations confirms that each event is more than just random noise. If the same ripple appears on each, it must be coming from somewhere in the sky.
Time-stamping the exact arrival time of waves at each arm of the observatory, and at each different observatory around the world, helps pinpoint the direction of the wave and the position of the wave source.
And the chirps these detectors pick up can reveal more than just the final moments when giant objects coalesce.
If astronomers are lucky enough to detect both gravitational waves and light from a colliding body, as happened in 2017 with a neutron star merger called GW170817.
Its rich dataset will allow us to measure the expansion rate of the universe and perform better tests of Einstein’s general theory of relativity.
GW170817 showed scientists just how much gold, platinum, and other heavy metals could be thrown into space by this kind of high-energy explosion.
There are currently 93 confirmed mergers. Astrophysicists hope to double the catalog of collisions in the next 18 months, transforming the once-rare chirping into a cosmic choir, a growing soundscape of the universe’s most epic or silent collisions. I believe.
