Every ray aimed inside this dark disc falls into the black hole. It is about 2.6 times wider than the event horizon itself.
The photon ring
The thin bright ring hugging the shadow is light that looped around the hole, sometimes more than once, before escaping to you.
The disk above and below
The glowing arc over the top is the far side of the disk. Gravity bends its light up and over the hole. The fainter arc underneath is the disk's underside.
One bright side
Gas on the inner edge orbits at half the speed of light. The side rushing toward you is boosted brighter and bluer; the receding side dims and reddens. Light climbing out of the gravity well is also redshifted.
Jets
Some black holes launch plasma from their poles at nearly light speed: wound into strands by magnetic fields, strung with shocks that glow as knots, or flaring inside a wide cone. The jet pointing toward you is beamed far brighter than its twin, which can also appear bent around the shadow.
Two black holes
In a binary, each hole bends the other's light, so you can see a companion's disk wrapped around its partner as they orbit.
Warped stars
The whole sky is lensed. Stars near the shadow are magnified into brief flashes and duplicated on opposite sides of the hole. The nearest stars lie at different distances, like the cluster around the Milky Way's own black hole, so they shift against the distant sky as you move.
The backgrounds
Artistic recreations of famous nebulae photographed by Hubble and Webb, and Webb's first deep field, whose distant galaxies are bent into arcs by a galaxy cluster's own gravity. Each is placed behind the hole, wherever you are looking, near enough to shift a little as you move, and the hole lenses it like everything else. Choose one under the title, or roll the dice.
The star
A short, bright life
Only stars born with more than about 20 times the Sun's mass are thought to end as black holes. They burn through their fuel in a few million years; lighter stars leave neutron stars or, like the Sun, white dwarfs. Start from the star with Switch to Sun, under the title.
Granulation
The surface, the photosphere, is tiled with granules: columns of hot gas welling up from inside, cooling and sinking again at their dark edges. On the Sun most are about 1,000 km across and last around ten minutes.
Sunspots
Where tangled magnetic fields break the surface, they hold back the heat rising from below. The spots are about 1,500 K cooler than their surroundings and look dark only by contrast.
Prominences
Arches of cooler, denser plasma held above the surface by magnetic loops, sometimes for weeks. Some erupt and hurl billions of tonnes of gas into space.
The corona
The star's thin outer atmosphere, heated to more than a million kelvin, hundreds of times hotter than the surface beneath it. Exactly how is still being worked out. From Earth, the Sun's is seen during total eclipses.
Its colour
A star's surface temperature sets its colour: red below about 3,700 K, yellow-white like the Sun at 5,800 K, blue-white above 10,000 K. The letter beside the temperature in the settings is its spectral class, from hot O to cool M.
Not to scale
Here the star is only a few times wider than the black hole it leaves (six times, at the default mass). A real one would be tens of thousands to tens of millions of times wider: the hole is only tens of kilometres across.
The supernova
Core collapse
A massive star fuses ever heavier elements in its core, up to iron, which yields no energy. Once the iron core outgrows about 1.4 Suns it can no longer hold itself up and collapses in under a second, from about the size of the Earth to a ball of neutrons some 20 km across, falling at up to a quarter of the speed of light.
The bounce
The infalling layers rebound off the new neutron core and a shock wave runs outward. Neutrinos carry off about 99% of the energy released: those from Supernova 1987A reached Earth hours before its light.
Shock breakout
The shock takes hours, up to a day in a giant star, to reach the surface. When it breaks out, a flash of ultraviolet light and X-rays comes first; then the whole star swells and blazes.
The debris
The star's outer layers fly off at around 10,000 km/s. For weeks a supernova can outshine its entire galaxy, and it scatters the oxygen, silicon, calcium and iron made in the star and the blast into space, for future stars and planets.
Remnants
Over centuries the debris spreads into a remnant like Cassiopeia A, a glowing shell about ten light-years across, or the Crab Nebula, one of the backgrounds here, left by a supernova seen from Earth in 1054.
The birth of the black hole
Fallback
In the most massive stars the shock cannot throw everything off. Gas falls back onto the young neutron star until it passes the most a neutron star can hold, two to three Suns, and it collapses into a black hole, within seconds to hours. Some stars may collapse with hardly any explosion at all.
Collapsars and gamma-ray bursts
If the star was spinning fast, gas falling in swirls into a disk around the newborn hole, which can launch jets that drill out through the star at nearly the speed of light. Pointed at us, they are seen as a long gamma-ray burst, the most luminous kind of explosion known.
Light follows exact photon orbits of a non-spinning (Schwarzschild) black hole, seen by an observer hovering in place. A binary is approximated by adding each hole's pull. The disk's brightness profile, colours and time-lapse speed are artistic; the nebulae are not to scale, and nor are the star and its supernova, which squeeze hours and centuries into seconds.
Event Horizon
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