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Loading contentThe end-states of gravity — the geometry of a black hole from its horizon to its singularity, the jets it launches, and the neutron star: a Sun crushed into a city, spinning as a pulsar and holding matter denser than an atomic nucleus. From the physics to the real objects in the sky.
The region just outside the event horizon of a rotating (Kerr) black hole where spacetime itself is dragged around so fast that nothing can stay still relative to the distant stars. Energy can, in principle, be extracted from a black hole's rotation here through the Penrose process. A non-rotating black hole has no ergosphere.
The compact object of Cygnus X-1 — the first widely accepted black hole. A bright X-ray source in Cygnus discovered in 1964, it is a stellar-mass black hole of roughly twenty-one solar masses pulling gas from its blue-supergiant donor star (HD 226868). It was the subject of a famous bet between Stephen Hawking and Kip Thorne, which Hawking conceded in 1990.
The young neutron star at the heart of the Crab Nebula, formed in the supernova recorded by observers in 1054. It spins about thirty times a second and is the archetypal rotation-powered pulsar, its wind lighting up the surrounding nebula across the spectrum, from radio to gamma rays.
A rapidly rotating, magnetised neutron star observed as a source of regular pulses of radiation, usually in radio. The first was found in 1967 by Jocelyn Bell Burnell and Antony Hewish; thousands are now known, with periods from milliseconds to seconds. Pulsars are precise cosmic clocks used to test gravity and to search for gravitational waves.