Black Hole Simulator

Explore light around black holes, or build a scene of your own.

How to use the black hole simulator

Choose a scene from the list to open it. Drag to orbit, scroll or pinch to zoom, and use the camera angles for classic views: Edge on shows a disc's far side arching over the black hole, From above shows it face on, and Close up fills the sky with bent starlight. Fall in carries you down toward the selected black hole.

The buttons at the top switch parts of the physics on and off so you can see what each one does:

• Disc hides all the glowing gas and jets, so you see the shadows and the lensed Milky Way alone.
• Doppler turns off the brightening and blueing of gas coming toward you.
• Lensing makes light travel in straight lines, as it would without gravity. Compare the two and the size of the effect is startling.

Play runs the scene: discs turn and objects orbit one another. The buttons beside it slow the orbits down or speed them up.

Build your own scene

Press Add, choose Black hole or Star, and click or tap in space. The camera steps back to make room, and the new object starts on a circular orbit around the heaviest black hole. A scene holds up to four black holes and three stars.

Click a black hole's shadow, a name tag, or choose an object in Details to select it. For a black hole you can set:

• its mass, which sets its size: a black hole twice as heavy is twice as wide, and so is its shadow;
• what surrounds it: a thin disc, glowing gas or nothing;
• the disc's size, tilt and colour, from cool red-orange to very hot blue-white;
• a jet along its axis.

A star has a surface temperature, which sets its colour, and a size. Drag an object's name tag to move it, or focus the tag and use the arrow keys; it settles into orbit around the heaviest black hole, and the rest of the scene adjusts so it does not drift away. Delete removes the selected object, Undo steps back through your changes and Start the scene again returns to the scene as it opened. With two or more black holes, Details shows how far apart the two heaviest are, how long one orbit takes and, with Gravitational waves on, roughly how long they have before they merge.

Share copies a link to the current view. When you have built or changed a scene, the whole scene travels in the link after the #, which browsers never send to a website; the link opens it paused. More holds picture download, full screen, reset view, focus mode and graphics detail.

The scenes

A single non-rotating black hole looks the same at any mass once you zoom to match its size. Its mass sets the real-world scale in Details, from the size of the event horizon to how long an orbit at the inner edge of the disc takes. What changes the picture is what surrounds a black hole, how you view it, and the other objects around it.

Try following the light

Open the paused lensing experiment. Keep the camera in place and switch Lensing off, then on. Which parts of the far side of the disc become visible above and below the shadow?

Next compare Doppler on and off. The change in brightness across the disc comes from the gas moving toward and away from the camera. Then open A star behind a black hole, press Play and watch the star's image stretch into a ring as it passes behind.

To compare a different kind of gravity effect, try a circular and escaping orbit. That experiment follows massive bodies; this one follows light.

What you are seeing

The shadow. The dark centre is not the event horizon itself but the black hole's shadow. Any light that passes closer than about 2.6 Schwarzschild radii is captured, so the shadow appears about two and a half times wider than the horizon.

The photon ring. Just outside the shadow, light can loop around the black hole once, twice or more before escaping. Each loop makes a thinner, fainter copy of the whole scene, stacked into bright rings at the shadow's edge.

The disc. Gas spirals in and heats up as it goes. Its temperature peaks just outside the innermost stable circular orbit, three Schwarzschild radii from the centre, where the gas moves at half the speed of light. Inside that, gas plunges straight in, so the disc has a sharp inner edge. The turbulence in the disc shears as it turns, because the inner gas orbits faster than the outer gas.

Glowing gas and jets. Black holes that are fed slowly, like Sagittarius A* and M87*, are wrapped in a thick, faint, very hot flow instead. Some also launch jets along their axis. Jet particles move close to the speed of light, so the jet coming toward you looks far brighter than the one going away.

The arch. Light from the part of a disc behind a black hole is bent over the top and under the bottom, so you see the far side of the disc as a bright arch, the image made famous by the film Interstellar.

The sky. Behind the black holes, the Milky Way is warped into arcs and, where it lines up exactly, into an Einstein ring.

The physics

A non-rotating black hole of mass M has an event horizon at the Schwarzschild radius, rs = 2GM/c². For light, Einstein's equations reduce to one orbit equation, u″ + u = (3/2) rs u², where u is one over the distance from the centre. The simulator writes that equation in Cartesian form and integrates it for one ray per pixel, starting at the camera and running backward in time, until the ray falls into a horizon, escapes to the distant sky, crosses a disc or reaches a star.

With several black holes, each one adds its own bend to the ray. That is exact for a single black hole and matches Einstein's theory far from them all, where small bends add up. Where light passes close to two black holes at once it is an approximation: no exact solution for two black holes exists.

Where a ray crosses a disc, the colour comes from the gas temperature and two shifts. The gravitational redshift factor, √(1 − rs/r), dims light climbing out of the well. The Doppler shift, 1/[γ(1 − β cos θ)], brightens and blues gas moving toward the camera, including the motion of its black hole around a companion. Brightness scales as the fourth power of the combined shift, so the approaching side can outshine the receding side several times over.

Objects orbit one another under Newton's gravity. With Gravitational waves on, each pair of black holes loses the energy Einstein's quadrupole formula gives for a circular orbit, as Peters worked out in 1964, so the orbit shrinks ever faster; two black holes that meet become one with 95% of their combined mass.

How we check it

The ray tracer's equation and step rule are tested every time the site is built, using the same code in JavaScript:

• The capture threshold, which sets the shadow's size, lands within 1% of √27/2 rs, for the single-hole integrator and for the multi-hole one given a single hole.
• A black hole twice as heavy, placed anywhere, casts a shadow twice as wide, to 1%.
• Rays that skim the threshold circle the photon sphere at 1.5 rs.
• Far from the hole, light bends by 2rs/b, the deflection Eddington measured during the 1919 solar eclipse, to within 1%. Two black holes on either side of a ray bend it by the sum of their separate bends, to within 5%.
• Gas at the innermost stable orbit moves at exactly half the speed of light, and a clock there runs at √(2/3), about 82%, of the far-away rate.
• The merging pair spirals in within 15% of the time Peters's formula predicts, and without wave losses the same pair keeps its orbit.

Limits

These black holes do not spin. A spinning (Kerr) black hole, which most real ones are, has a slightly flattened, off-centre shadow and a disc that reaches closer in. Discs are thin, glowing gas and jets are simple models, and their colours represent relative temperature. Your camera hovers in place, so its own motion does not distort the view, as a falling camera's would. Orbits use Newton's gravity, stars are drawn far smaller and closer than life, and light between two close black holes follows the approximation described above.

For orbit experiments with planets and stars, use the Newtonian gravity sandbox. The sources and model comparison distinguish those limits; NASA's black-hole overview provides broader astronomical context.

Sources

Checked September 30, 2026:

• Event Horizon Telescope Collaboration, First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole, 2019: M87*'s mass, 6.5 billion solar masses.
• GRAVITY Collaboration, The mass distribution in the Galactic Centre from interferometric astrometry of multiple stellar orbits, 2022: Sagittarius A*'s mass, 4.30 million solar masses.
• Event Horizon Telescope Collaboration, First Sagittarius A* Event Horizon Telescope Results. I., 2022.
• Miller-Jones and others, Cygnus X-1 contains a 21-solar mass black hole, 2021: 21.2 solar masses.
• LIGO Scientific and Virgo Collaborations, Observation of Gravitational Waves from a Binary Black Hole Merger, 2016: 36 and 29 solar masses merging into 62.
• P. C. Peters, Gravitational Radiation and the Motion of Two Point Masses, 1964.