black-hole [view|disk|sky|look|about] presetThe picture is computed live on your graphics card: for every pixel a light ray is followed backwards through the curved space around the black hole.
Start with one of six presets above the picture: Gargantua (the film look), M87* and Sgr A* (the two black holes photographed by the Event Horizon Telescope), Quasar, Cygnus X-1 and Edge-on. Keys 1–6 work too, and the View tab says what each one stands for.
Drag the picture to orbit, scroll (after clicking it) or pinch to zoom. Inclination is measured from the spin axis: 0° looks straight down onto the disk, 90° looks along it. Orbit drift turns the sky slowly, which makes a good screensaver.
In Disk set the peak temperature (which sets the colour), brightness, turbulence, flow speed, size and the corona glow, or switch the disk and Doppler beaming off to see what they add.
Sky sets the stars and the Milky Way. Look sets exposure, bloom, film grain, vignette and lens fringing, and switches on labels that mark the shadow edge and which side of the disk moves toward you.
Save image renders a sharp JPEG of the current view, up to 2,400 pixels wide. Copy link puts all settings into the address, and Full screen hides everything but the picture. Your settings are remembered in this browser.
A black hole bends the light around it so strongly that the back of its accretion disk appears arched over and under the dark shadow, and the stars behind it are smeared into rings. This page reproduces that by following a light ray for every pixel through the curved space around a non-rotating (Schwarzschild) black hole, in real time on your graphics card. Nothing is a picture of a black hole: the shape comes out of the calculation.
The light paths are exact for a non-rotating black hole. Each ray is followed with the Schwarzschild orbit equation for light, so the lensed far side of the disk, the second and third images of the disk squeezed into the thin photon ring, the 2.6 rs radius of the shadow and the way stars are stretched into arcs all appear on their own. Colour and brightness follow the physics too: every point of the disk gets a Doppler and gravitational shift from the real formula for gas in a circular orbit, and its colour is that of a black body at the shifted temperature. What is simplified: the black hole does not spin (a spinning one, like the one in Interstellar, has a flattened, shifted shadow), the disk is thin and its turbulence is made up, the corona is a plain glow, and the disk neither lights itself nor adds to the gravity.
Gas near a black hole circles at up to half the speed of light. The side moving toward you is shifted to higher energy, so it looks hotter, bluer and much brighter; the side moving away is shifted down, redder and dimmer. This is Doppler beaming, and it is why the Event Horizon Telescope image of M87* is brighter on one side. Gravity adds a second effect, gravitational redshift: light climbing out of the deep well near the inner edge loses energy, so the inner disk is dimmer than it would otherwise be. The Doppler beaming switch removes the first effect and keeps the second, which gives the even look of the film Interstellar. The labels button marks the approaching and receding sides.
The photon ring. Light that passes close to 1.5 rs can circle the black hole once or more before it escapes, so the disk and the sky show up again, smaller and thinner, with every extra lap. The picture adds these images up into a bright hairline at the edge of the shadow. Its size does not depend on the disk or on how fast the black hole eats: it is set by the mass of the black hole alone.
Inclination is measured from the spin axis, as astronomers do: 0° means looking straight down onto the disk, 90° means looking along it. The presets use the same numbers as the real objects: M87* is seen at about 17° (the angle of its jet), which is why it looks like a ring, while the film look is about 84°.
Gargantua is a warm, thin disk seen from just above its plane, with beaming off. M87*, six and a half billion Suns, and Sgr A*, 4.3 million Suns, are the two black holes photographed by the Event Horizon Telescope: cool, orange and lopsided, with a strong glow near the shadow. Quasar is a very hot, bright disk around a billion-Sun black hole. Cygnus X-1 is a black hole of about 21 Suns that feeds on a companion star. Edge-on looks exactly along the disk. Each preset only sets sliders, and the View tab shows the real size of one rs and the orbit time at the inner edge for its mass.
The colour of each point is the colour of a black body at its temperature, converted for your screen, and the brightness follows the same curve, so a cooler spot is both redder and fainter. The temperature profile of the disk is the standard one for a thin disk, peaking just outside the inner edge. The peak temperature itself is a free choice: a real disk around a supermassive black hole is much cooler and glows in infrared or radio, one around a star-sized black hole is millions of degrees and glows in X-rays, so the visible colours here are for looks.
Leave Quality on Auto: it lowers the render resolution and the number of ray steps when the frame rate drops and raises them again when there is room. You can also pick Low, switch the corona and the bloom off, or make the window smaller. A phone or a laptop on battery is happiest on Low or Medium.
Once the page is open it runs entirely on your graphics card and downloads nothing more, so it keeps going if your connection drops. The page is not installed for offline use, so opening or reloading it needs a connection.
Yes. Pick a preset, set Orbit drift, press F for full screen and H to hide the controls. The sky turns slowly around the black hole and the disk keeps flowing.
There is no account, and nothing you do is sent anywhere. The page loads its font from Google Fonts and page statistics from SimpleAnalytics, and it makes no other network requests. Your settings (preset, sliders, quality and the camera) are stored in your browser under bh-settings-v2 so they are still there next time. Copy link puts the settings in the address after a # sign, which a server never receives. Save image draws the picture and saves it on your device without uploading it.