The “ringing” from a merging black hole is a fading pattern in gravitational waves—not a sound travelling through space. In observations including GW150914 and the newer GW250114, LIGO measured signals that agree with general relativity’s predictions for black-hole mergers and with the prediction that a black hole’s event-horizon area does not decrease. These results support Einstein’s theory and test a classical theorem associated with Stephen Hawking; they do not prove every aspect of Hawking radiation or rule out every alternative theory of gravity.
What is a black-hole ringdown?
When two black holes merge, they form a single remnant black hole. If that remnant is distorted, it settles toward a stable state by emitting gravitational waves. This fading final part of the waveform is called the ringdown.
In general relativity, the ringdown’s characteristic frequencies and damping rates—the rates at which its oscillations fade—are determined by the remnant’s mass and spin. Comparing the observed pattern with the predicted one therefore tests whether the remnant behaves like a rotating Kerr black hole, the type described by Einstein’s theory.
The signal is a changing pattern in spacetime that detectors can measure, not an acoustic wave in space. It can be converted into sound for listening, but that conversion does not mean the original signal was audible.
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How did GW150914 test Einstein’s theory?
On 14 September 2015, LIGO observed GW150914, the first confirmed gravitational-wave signal from merging black holes. The source was about 1.3 billion light-years away. LIGO and Virgo announced the discovery on 11 February 2016. The collaboration reported a signal-to-noise ratio of 24 and a false-alarm rate below one event per 203,000 years.
The test was not limited to the final “ringing.” The waveform matched general relativity’s predictions across the inspiral, merger and ringdown: the black holes spiralling together, their collision, and the settling remnant. That agreement provided the first direct evidence that black holes merge and a major test of Einstein’s predictions in an extreme-gravity system.
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What was GW250114, and what did it add?
GW250114 is a later black-hole merger observation discussed by LIGO in 2025. LIGO reported that its ringdown modes occurred as predicted by calculations using the Teukolsky formalism, a framework used to calculate gravitational-wave behaviour around black holes. The result provided a sharper test of the expected ringdown pattern and of the area theorem than the earlier GW150914 analysis.
The two observations play different roles: GW150914 established the first confirmed detection of gravitational waves from merging black holes and tested the full predicted waveform; GW250114 provided a later, more precise test of ringdown and the area law. The reported results do not provide every comparison detail—such as a specific observation date for GW250114 or numerical remnant-mass and spin precisions—in the cited accounts summarized here.
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| Comparison | GW150914 | GW250114 |
|---|---|---|
| Role in the result | First confirmed gravitational-wave observation from merging black holes (LIGO Scientific Collaboration, 2016). | Later ringdown and area-law test reported by LIGO Laboratory in 2025. |
| Observation date | 14 September 2015 (LIGO Scientific Collaboration, 2016). | Not stated in the cited LIGO Laboratory account (2025). |
| What the waveform test established | Agreement with general-relativistic predictions for inspiral, merger and ringdown (LIGO Scientific Collaboration and Virgo Collaboration, 2016). | Reported ringdown modes matched Teukolsky-formalism predictions (LIGO Laboratory, 2025). |
| Area-theorem result | Agreement at 97% probability when ringdown overtones were included, and 95% without them (Physical Review Letters authors, 2021). | LIGO reported a 99.999% confidence test of the area theorem (LIGO Laboratory, 2025). |
| Numerical remnant-mass and spin precision | Not stated in the cited accounts summarized here. | Not stated in the cited LIGO Laboratory account (2025). |
Did Hawking’s black-hole area theorem pass a test?
The area theorem concerns a black hole’s event horizon: under the classical assumptions of general relativity, the total horizon area cannot decrease. In a merger, the combined remnant’s area should therefore be at least as large as the sum of the initial black holes’ areas.
That classical prediction is distinct from Hawking radiation. The ringdown and area-law analyses described here test the classical area theorem and black-hole predictions derived from general relativity; they are not direct observations of Hawking radiation.
For GW150914, the 2021 Physical Review Letters analysis found agreement with the area theorem at 97% probability when ringdown overtones were included, and 95% without them. Overtones are additional, more rapidly fading components of the ringdown signal. LIGO Laboratory’s 2025 account reported a 99.999% confidence area-theorem test for GW250114.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How certain are these results—and what do they not show?
The percentages are statistical results within the analyses and models used; they are not a guarantee that every prediction of general relativity is true. The GW150914 signal-to-noise ratio and false-alarm rate describe the strength and statistical significance of that detection, while the area-theorem probabilities and confidence describe tests of a specific prediction. They measure different things.
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Together, the observations support general relativity’s description of black-hole mergers and the classical area theorem, with the later result sharpening the ringdown test. They do not logically exclude every alternative theory of gravity, establish every property of black holes, or test all of Hawking’s work.
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