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Event Horizon

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// system ready

Event Horizon

Dive toward a black hole for crystals and get back to the mothership. Near the hole time slows down, starlight bends and there are no stable orbits below 3 rs — general relativity in action.

  1. 1Hold the left mouse button — the ship turns to the cursor and fires the engine. Or W — thrust, A/D — turn. The dotted line shows where your orbit takes you.
  2. 2Space or S — autopilot: matches the speed of a circular orbit, and near the mothership steers you in to dock.
  3. 3Collect crystals on orbits (the closer to the hole, the more they are worth) and bring them to the mothership. Fuel and hull refill there too.
  4. 4Orbits below 3 rs are unstable, and past the horizon (1 rs) there is no way back. Complete 5 missions — the last one right next to the hole.
About, tips and FAQ

About the game

Event Horizon is a science game about black holes and general relativity. You fly a small ship from a mothership down toward a black hole, collect crystals on orbits and bring them back.

Orbits use the Paczyński–Wiita potential, which exactly reproduces two key results of general relativity: the innermost stable orbit at 3 Schwarzschild radii and the marginally bound orbit at 2 rs. Clocks near the hole run slower by √(1 − rs/r), light from distant stars bends (gravitational lensing), and the hole’s shadow is 2.6 times wider than its horizon.

All of this is gameplay: deeper crystals are worth more, but below 3 rs a ship without thrust falls in. One mission asks you to make the crew age more than you — just like in films about trips to black holes. Play free in the browser on desktop and mobile.

Tips

  • Watch the dotted line: it is your future orbit. If it ends with “falling!”, fire the engine outward right away.
  • Space or the Orbit button matches circular-orbit speed — the easiest way to reach a crystal.
  • To go lower, burn against your motion; to climb, burn along it.
  • Don’t burn all your fuel down deep: climbing out costs more than diving in.
  • During a disk flare climb above 4 rs, and when a star is torn apart, go for the golden crystals.

FAQ

What is an event horizon?
The boundary of a black hole from which not even light can escape. Its radius is the Schwarzschild radius rs = 2GM/c² — about 3 km for the Sun.
Why does time run slower near a black hole?
Gravitational time dilation from general relativity: clocks in strong gravity run slower by a factor of √(1 − rs/r). At 2 rs that is about 1.4 times slower.
Why are there no stable orbits below 3 rs?
In general relativity gravity near the hole is stronger than Newton’s. From 3 rs inward any small error in speed sends a body down, which is why the disk of matter around a hole starts there.
Why do stars around the hole appear twice?
Gravitational lensing: the hole bends light, so rays from one star reach us from both sides. A star exactly behind the hole becomes an Einstein ring.