Black holes are real
Spacetime can curve so steeply that light cannot escape. Mergers of such objects have been heard in gravitational waves and imaged in radio light.
Karl Schwarzschild found a solution to Einstein’s equations in 1916 that hid a region from which nothing returns. For decades it was treated as a mathematical curiosity. Stars were not supposed to collapse that far.
On 14 September 2015 the LIGO detectors rang with GW150914: two black holes of about 36 and 29 solar masses merging 1.3 billion light-years away. The waveform matched general relativity. Since then, dozens of mergers have been catalogued.
In 2019 the Event Horizon Telescope published an image of the shadow of M87*, a supermassive black hole. In 2022, Sagittarius A* at the centre of our own galaxy. The objects are no longer hypothetical. They are on the map.
Caveats
- The interior of the horizon is not observed. The singularity is a sign that the theory is incomplete, not a photographed object.
- Hawking radiation remains unmeasured for astrophysical holes.
Sources
- 1Abbott B. P. et al. (LIGO/Virgo). Observation of Gravitational Waves from a Binary Black Hole Merger. Physical Review Letters 116, 061102, 2016.
- 2Event Horizon Telescope Collaboration. First M87 Event Horizon Telescope Results. Astrophysical Journal Letters 875, L1, 2019.