When spacetime curves so much that nothing escapes
Pack enough mass into a small enough space and not even light can escape. Here you can bend starlight, fire photons at a black hole, and set one spinning.
Drag the black hole across the starfield and watch stars warp into arcs and an Einstein ring. Change the mass to see the dark shadow and the ring grow.
Drag the black hole across the starfield. Stars warp around the photon sphere, forming Einstein rings and multiple images. The dark shadow is the photon capture radius — light that enters never escapes.
When enough mass is concentrated in a small enough region, spacetime curves so severely that nothing — not even light — can escape. The boundary of no return is the event horizon. Beyond it, all paths lead inward toward the singularity. Black holes are not exotic curiosities; they are the inevitable endpoint of massive stellar evolution, and supermassive ones anchor the cores of most galaxies.
A black hole warps the fabric of spacetime so severely that light from background stars is bent, magnified, and distorted. Stars directly behind the black hole form a bright Einstein ring. Nearby stars appear doubled, stretched into arcs, or dramatically displaced from their true positions.
Try it: Drag the black hole across the starfield and watch stars warp and dance around it. The dark shadow in the center is the photon capture radius — light that enters never escapes. Adjust the mass to see how the shadow and Einstein ring scale.
Set the impact parameter and launch photons, or fire a whole spread at once. Watch light get captured, circle at the photon sphere (r = 3M), or escape.
A Schwarzschild black hole has three critical radii: the event horizon at r = 2M (point of no return), the photon sphere at r = 3M (where light orbits in circles), and the ISCO at r = 6M (innermost stable circular orbit for massive particles). Launch photons at different impact parameters to see capture, orbiting, and deflection.
Click anywhere on the diagram to place an event and see its causal future. Inside the horizon, every future path ends at the singularity along the top.
The Penrose diagram of Schwarzschild spacetime reveals the full causal structure. The singularity is a horizontal line at the top — it's not a place in space, but a moment in the future. Once inside the horizon, hitting the singularity is as inevitable as Tuesday following Monday.
Turn up the spin and watch the ergosphere bulge out beyond the event horizon as nearby particles are swept around.
Real black holes rotate. A rotating (Kerr) black hole drags spacetime around with it — an effect called frame dragging. Outside the event horizon lies the ergosphere, a region where no object can remain stationary, as spacetime itself is swept along faster than light.
Press Play and watch particle pairs split at the horizon as the black hole loses mass. Start from a smaller mass: smaller black holes are hotter and evaporate faster.
Virtual particle-antiparticle pairs spontaneously form near the event horizon. Occasionally one particle escapes while its partner falls in, causing the black hole to lose mass and slowly evaporate. Smaller black holes are hotter and radiate faster.
Quantum mechanics adds a twist: black holes aren't perfectly black. Near the event horizon, virtual particle-antiparticle pairs are separated — one falls in, the other escapes as Hawking radiation. Over astronomical timescales, the black hole slowly evaporates, posing deep puzzles about information and the nature of spacetime.
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