A supermassive black hole is humming a deep B-flat
While space is famously silent because vacuums cannot carry sound waves, some regions are different. In the Perseus galaxy cluster, hot gas surrounds a supermassive black hole. The black hole releases pressure waves that ripple through this dense gas, creating a real acoustic sound. The pitch is a B-flat, 57 octaves below middle C—far too deep for human ears.
Sound Waves Across an Intergalactic Medium
A common rule of thumb in astronomy is that sound cannot travel through the vacuum of space. Because sound is a mechanical wave that propagates by compressing and expanding matter, it requires a medium—such as air, water, or solid rock—to carry its energy. In the vast emptiness between stars, the density of particles is generally far too low to support these pressure oscillations, leaving most of the cosmos completely silent.
Galaxy clusters provide a rare exception to this rule. A massive galaxy cluster is not merely an assortment of isolated galaxies floating in empty space; it is embedded in a vast, diffuse reservoir of plasma known as the intracluster medium. In massive clusters like the Perseus Cluster (also cataloged as Abell 426), this intergalactic gas reaches temperatures of tens of millions of degrees and contains enough particle density to transmit genuine pressure waves across millions of light-years.
The Central Engine of NGC 1275
At the core of the Perseus Cluster lies NGC 1275, a dominant central galaxy hosting an active supermassive black hole. As matter swirls toward the event horizon, immense gravitational and electromagnetic forces launch powerful relativistic jets of particles outward into the cluster environment. These jets plow into the surrounding intracluster gas, carving out enormous cavities or bubbles filled with relativistic plasma.
The cyclical expansion and inflation of these gas cavities act like a cosmic piston. Each time the central engine erupts, it pushes against the surrounding hot gas, sending shockfronts and acoustic ripples rolling outward in concentric rings. Rather than being a continuous roar, the energy is released in discrete, quasi-periodic pulses that generate coherent sound waves in the plasma.