Supermassive Black Hole
A photorealistic rendering showing:
- Gravitational lensing of background stars
- Doppler-shifted accretion disk
- Photon ring at 1.5x Schwarzschild radius
- Einstein ring amplification
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A photorealistic rendering showing:
A 3D grid shows how mass warps the fabric of spacetime. The deeper the well, the stronger the gravitational pull and the slower time flows relative to a distant observer.
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Light rays (geodesics) curve in the gravitational field. Rays passing within 1.5 Rs are captured. At exactly 1.5 Rs, photons orbit indefinitely — the photon sphere.
Move mouse to aim light rays.
General Relativity describes how mass curves spacetime, and how that curvature determines the paths of light and matter.
The simplest black hole: non-rotating, uncharged, spherically symmetric.
This is the exact solution to Einstein's field equations for a spherical mass. It describes how spacetime geometry changes with distance r from the center. When r = rs, the metric becomes singular — this is the event horizon.
The radius at which the escape velocity equals the speed of light. For the Sun, rs ≈ 3 km. For Sagittarius A*, rs ≈ 12 million km.
How mass bends the path of light passing nearby.
A light ray passing a mass M at closest approach distance b (impact parameter) is deflected by angle α. This is exactly twice the Newtonian prediction — the factor of 2 was the key test that confirmed General Relativity in 1919.
When a light source, lens, and observer are perfectly aligned, the source appears as a bright ring. The angular radius depends on distances between observer, lens, and source.
Critical radii where light behaves strangely.
At this radius, photons travel in unstable circular orbits. A slight perturbation sends them spiralling inward (captured) or outward (escaping). This creates the bright photon ring visible in images of black holes.
The inner edge of the accretion disk. Matter inside this orbit cannot maintain a stable orbit and spirals rapidly into the black hole, emitting intense radiation as it falls.
Light rays with impact parameter b < bcrit are captured by the black hole. This defines the apparent size of the black hole's "shadow" — the dark silhouette seen in the Event Horizon Telescope image of M87*.
Time runs slower in stronger gravitational fields.
Proper time τ (experienced by an observer at radius r) flows slower than coordinate time t (measured by a distant observer). At the event horizon (r = rs), time stops completely from the outside perspective.
Light climbing out of a gravitational well loses energy and shifts to longer (redder) wavelengths. Near the event horizon, light is infinitely redshifted and can never escape.
Black holes aren't completely black — they slowly evaporate.
A black hole radiates as a blackbody with temperature T. Smaller black holes are hotter. A solar-mass black hole has T ≈ 60 nanokelvin — far colder than the cosmic microwave background.
A black hole's entropy is proportional to its surface area A, not its volume. This is the foundation of the holographic principle — all information inside a black hole is encoded on its 2D horizon.