This is what black holes sound like
Gravitational waves are an abstract phenomenon. Almost no one can imagine space-time distortions. An artist and a composer are now making the waves emitted by merging black holes tangible.
AOn September 14, 2015, scientists were able to measure gravitational waves for the first time and thus prove their existence. About 100 years earlier, Albert Einstein deduced the existence of these waves from the formulas of the general theory of relativity, but he himself did not believe that these small distortions of cosmic space-time could ever be measured. Progress, especially in laser technology, eventually made it possible to build detectors that could pick up such signals.
And so the two LIGO gravitational wave detectors in the US, 3,000 kilometers apart, recorded signals at just the right time interval from each other, the shape of which was exactly as expected based on theoretical calculations. Based on these models, the researchers were able to determine in the next step that the measured gravitational wave was caused by two black holes emitted 1.3 billion light years away from us.
These two gravitational monsters revolved around each other, getting closer and closer to each other and finally merging to form a black hole. From the frequencies of the gravitational waves emitted during this process, physicists were able to calculate that the two black holes had 29 and 36 solar masses, respectively, before they merged.
The first direct detection of gravitational waves – the signal was named GW150914 – was a scientific sensation. Not only because after a century it confirmed the general theory of relativity, but also because it opened a completely new window for the observation of cosmic processes.
Measuring gravitational waves has become routine and such a signal is received from the depths of space every three days on average. Whenever large masses are strongly accelerated, they emit some energy in the form of gravitational waves. Characteristic gravitational waves are also emitted when two neutron stars merge or between a black hole and a neutron star.
When two massive objects in space merge, they become faster and faster as they get closer, causing the frequency of the gravitational wave to get higher and higher before the signal goes silent after the merger occurs. The nature of gravitational waves and acoustic waves is completely different. However, the wavelengths of gravitational waves emitted by merging black holes are often in a frequency range that, relative to sound waves, is in the range audible to the human ear.
Gravitational wave researchers immediately had the idea that this analogy could be used to illustrate the phenomena. They use a computer to convert the measured gravitational wave frequencies into corresponding electrical signals, which can then be used to acoustically experience a gravitational wave using speakers.
The ever-increasing sound frequency creates a characteristic “tschirp” sound, which inspired artist Annika Kahrs to create a video work. Together with composer Louis d’Heudières and musicians from Los Angeles, she musically interpreted the “tschirp” sounds of various cosmic fusion events.
The film “Melody of Gravity” opens an artistic and poetic approach to the physical phenomenon of gravitational waves. The film-musical discussion is scientifically followed by Keith Thorne, who works as a physicist at LIGO. He calls the LIGO Research Institute the “quietest concert hall” in the world. Because during the highly sensitive measurement of gravitational waves with laser spectrometers, all types of terrestrial noise can be disturbing.
In Kahr’s film, Thorne is in the LIGO control room and in front of the orchestra at the conductor’s podium. There he announces with dignity: Listen to GW150914 now! The “Gravity’s Tune” video was created as part of the artist’s 2021 Villa Aurora fellowship in Los Angeles and was made possible by the MOIN Film Fund Hamburg Schleswig-Holstein and the Schering Foundation.
The symbiosis between physics and culture can be experienced in the exhibition space of the Schering Foundation in Berlin (Unter den Linden 32-34) until November 26, 2023. Free entry.
“Ah! Ten Minutes of Everyday Knowledge” is WELT’s knowledge podcast. Every Tuesday, Wednesday and Thursday we answer everyday questions in the field of science. Subscribe to the podcast on Spotify, Apple Podcasts, Deezer, Amazon Music or directly via RSS feed, among others.