black hole ringdown overtones

Imagine a lottery where instead of money, you win black holes. Each ticket is a random spot on the sky, and the prize is a gravitational wave from the merger of two giants. The chance of hitting the jackpot is minuscule, but if you do, the wave is heard across the entire universe.

The very first moment of the universe's existence is like a taut string suddenly struck. It vibrated, and those oscillations froze into galaxies and voids. But physicists suspect there were other vibrations — fast, local, almost like a drumroll against a slow melody.

A stone falls into still water — ripples spread across the surface. A black hole behaves similarly when something falls into it or when it merges with another black hole. The hole begins to oscillate, and these oscillations propagate through space as gravitational waves.

A spinning top that makes a hundred turns per second suddenly starts losing speed dramatically — much faster than any known top. That's exactly what pulsar J0435+3233 is doing. It's a dead star, crushed to the size of a city, but whirling at a furious rate.

In the first moments after the Big Bang, the Universe hummed like a bell. Inflation, the epoch of rapid expansion confirmed by measurements of the cosmic microwave background, ended, and the inflaton field began oscillating around the minimum of its potential.

A black hole merger is not a silent impact. The newborn hole quivers and decays, emitting gravitational waves — ripples in space itself. This signal is called the 'ringdown,' and it resembles the fading chime of a bell: it has a fundamental tone and several overtones.

A black hole can be compared to a bell: after being struck, it vibrates, emitting a decaying 'ring.' This ring is the gravitational waves that detectors on Earth pick up.

After a merger, the newborn black hole emits a fading tremble — gravitational waves, similar to a ringing bell. By analyzing the overtones of this signal, spectroscopy can determine its mass and spin rate.

Strike a bell, and it rings. But the sound isn't arbitrary: the bell itself picks out the notes to which its metal is tuned. It turns out a black hole behaves the same way. When something falls into it, or its spacetime gets warped, it starts to oscillate.

A giant drum has just taken a hit. Its membrane is still trembling, but besides the main boom, a fine ripple spreads across it — someone ran a finger over the taut skin. In much the same way, in the first moments after the Big Bang, spacetime vibrated not only with the "roar" of expansion but also with the tension of suddenly emerging magnetic fields.

Usually, black holes inch closer gradually, circling in a tightening spiral. This dance births a long ripple of gravitational waves — a tremor in the very fabric of spacetime. Detectors LIGO and Virgo routinely catch such mergers. But GW190521 is the exception.

Two heavy balls orbit on the surface of a pond. Ripples spread from them: these are gravitational waves. As the balls spiral closer, the waves carry away energy, and the ripples become more frequent.

When two black holes merge, the resulting black hole 'rings' for a while, emitting gravitational waves — like a dying bell. This ringing is captured by giant detectors created by Rainer Weiss and Kip Thorne.

A wormhole is a hypothetical tunnel that shortens the path between distant corners of the universe, like a soap bubble stretched between two points. To keep the bubble's walls from closing, a special film is needed — matter with negative pressure, akin to dark energy. But this support isn't eternal: remove half the film, and the bubble bursts.

Drop a stone into a pond — the ripples spread and fade away. A black hole, after colliding with another hole or a star, also 'rings', but its oscillations are not simple. Near the hole, 'overtones' sound — secondary waves born from the nonlinearity of spacetime itself.

The Big Bang was like a cosmic thunderclap that set the fabric of space vibrating. These vibrations — gravitational waves — still echo through the Universe like a fading rumble from that ancient event. The louder the initial 'bang,' the more primordial black holes should have formed.

Imagine the hum of a crowded square (that's what the gravitational wave background of the Universe sounds like, as detected by a network of pulsars) neutron stars that emit regular radio pulses with the precision of atomic clocks.

The black hole in the binary system Swift J1727.8-1613 flickers in X-rays like a campfire in the wind. But if you look closely at the rhythm of this flickering, you can see distinct 'humps'—bursts at specific frequencies, like drumbeats in the noise of a crowd.

A guitar string after being plucked produces not only the fundamental note, but also quiet overtones. A similar phenomenon appeared in the gravitational waves from the merger of two black holes (event GW250114).

A gravitational-wave detector catches not only the roar of mergers but also the quiet splash when a star or gas cloud dives into a supermassive black hole. Such a dive, like a stone falling into a well, generates waves at all frequencies at once—and in that spectrum lies encoded the nature of the well itself.