Frontier physics: black holes, galaxies and the universe

Open questions at the edge of physics, shown with real calculations. A black hole is ray-traced along curved light paths, a living galaxy shows why rotation curves point to dark matter, the universe expands under Hubble’s law, and an N-body simulation shows how quickly a few gravitating bodies turn chaotic.

This interactive simulation runs in your browser with WebGL. Free, no account needed.

What you can explore

Black hole

Every pixel’s light ray is traced backwards through Schwarzschild spacetime, so the accretion disc bends over and under the shadow and Doppler beaming brightens the side moving towards you.

Rotation curves

Stars in a spiral galaxy orbit at speeds that stay flat far from the centre, instead of falling off as the visible mass predicts. The gap between the two curves is the evidence for dark matter.

Hubble expansion

Galaxies recede with a speed proportional to their distance. The expansion looks the same from every galaxy, so there is no centre.

N-body

Three or four bodies pulling on each other: a stable figure-of-eight orbit, a binary with a passing probe, and a chaotic four-body system with no closed-form solution.

Key equations

  • v = H₀ d
  • v_kep = √(GM(r)/r)
  • r_s = 2GM / c²

Curriculum

IB Physics E.5, enrichment: astrophysics and cosmology.

Common questions

What is the evidence for dark matter from rotation curves?

Stars far from a galaxy’s centre orbit much faster than the visible matter could hold them. Extra unseen mass is needed to supply that gravity.

What is the black hole shadow?

The dark region where light rays fall into the event horizon. It appears larger than the horizon itself because gravity bends light around it.

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