Frame Dragging — Lense-Thirring Precession

Neutron Star

Mass 1.40 M☉

Spin period 3.0 ms

Test Orbit

Orbit radius 6.0 R★

Precession visual gain 3×

Live Readouts (real physics)

Frame-drag precession

— °/orbit

Orbital period

— ms

Full 360° precession takes

— orbits

How it works

General relativity predicts that a rotating mass drags spacetime itself around with it — frame dragging, described by the Lense–Thirring effect (1918). A gyroscope orbiting the star does not keep a fixed orientation relative to the distant stars: its spin axis slowly precesses around the star's rotation axis, and the local inertial frame near the star is literally swept along in the direction of spin.

In the weak-field, slow-rotation limit, the precession angular velocity of a gyroscope (or the "dragging" angular velocity of a local inertial frame) at equatorial radius r around a body with angular momentum J is:

Ω_LT = 2GJ / (c²r³)
J = I·ω_spin ,   I ≈ 0.35·M·R★²  (moment of inertia, uniform-density approx.)

This is the exact effect NASA's Gravity Probe B satellite measured around Earth (37.2 ± 7.2 milliarcseconds/year, matching GR's predicted 39.2 mas/yr) and the one invoked to explain jet and disk precession around real spinning neutron stars and black holes. Because a neutron star packs roughly a solar mass into a ~12 km sphere and can spin hundreds of times per second, Ω_LT close to its surface is enormous compared to Earth's — a test gyroscope a few stellar radii out precesses by a measurable fraction of a degree every single orbit, which is what this simulator renders directly from the formula above (no artificial slow-down needed at this scale; the small "visual gain" slider only stretches it a little further for clarity).

Mass / spin period — set the star's angular momentum J.
Orbit radius — where the six tilted gyroscope rings sit; frame dragging weakens as 1/r³, so pulling the rings out visibly slows their common precession.
Swirling arrows near the equator — the local frame-dragging angular velocity at four fixed reference radii, showing the drag falling off sharply with distance from the star.

Star spin axis Gyroscope spin axis Frame-drag swirl (reference shells)

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