Event Horizon Lab

A non-spinning black hole, ray-traced through curved spacetime. Drag to orbit, scroll or use the slider to zoom.

The black hole

Mass:

Event horizon radius

Light-crossing time

Tidal stretch at horizon

The picture looks the same at every mass. Mass changes the size, the timescales and the tides.

Drop a probe

Distance–

Your clock, far away–

The probe's own clock–

Light stretched by (1 + z)–

Tidal pull across a 2 m probe–

Warm bath it feels–

Probe–

One second on screen–

Watch it from here: it slows, reddens and fades at the edge, but never crosses.

The quantum side

Quantum mechanics makes a black hole glow faintly, like any warm object, and slowly lose mass. The smaller the hole, the hotter the glow.

Hawking temperature

Glow peaks at

Power radiated

Time to evaporate

Show the Hawking glow

Evaporate it

Mass left–

Real time passed–

Real time left–

The mass barely moves for most of the hole's life. Losing mass makes it hotter, which makes it lose mass faster, so the end is sudden.

The glow is often pictured as particle pairs splitting at the horizon. That picture is a helpful story, not the calculation. Whether what falls in is lost for good is the black hole information paradox, still unsolved.

Where does the information go? The Page curve

Entropy here counts how much you would need to know to pin down the exact state. Hawking's calculation says the radiation is thermal, so its entropy only ever climbs. But if physics never loses information, the radiation's entropy cannot exceed what the shrinking hole can hold: it has to turn over and fall back to zero.

The hole–

Radiation, Hawking–

Radiation, Page–

Page time–

Mass left by then–

In 2019, calculations using so-called islands reproduced this turnover from gravity itself, in simplified models. How the information actually gets out is still open.

Hold a probe still: the Unruh effect

An accelerating thermometer reads a temperature in empty space that a free-falling one does not. Staying put above a black hole takes rockets, so a hovering probe sits in a warm bath. Let it fall and the bath disappears.

Height above the horizon:

HoveringFalling Thrust to stay put0 g, weightless Warm bath it feelsnone Against the Hawking temperature–

On Earth, standing still takes 1 g, which puts you in an Unruh bath of 4 × 10⁻²⁰ K: far too cold to ever measure. Near a horizon the thrust, and the bath, grow without limit. The glow drawn around a hovering probe is false colour unless the bath is 1,000 to 40,000 K, and always exaggerated.

Sky

Camera distance:

Accretion disk Sky grid, to see the bending

Use my own sky image

Any image is wrapped around the sky and bent by the black hole.

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