Radiation-Pressure Blowout in a Debris Disk

Fresh Dust Grain Size

Grain radius s 2.0 µm

Star

Luminosity / Mass (L*/M*, ⊙ units) 1.00

Collisional Cascade

Dust production rate 30 /s

Live Readouts

β (radiation / gravity)

0.00

Blowout size s_blow

0.0 µm

Orbit eccentricity e

0.00

Grain fate

bound

Grains in flight

Ejected this run

How it works

A debris disk (Kuiper-belt analogue around another star, e.g. β Pictoris or Fomalhaut) is fed by a collisional cascade: planetesimals in the belt chip and shatter each other, continuously producing fresh micron-sized dust. Each new grain starts on essentially the same circular orbit as the rubble it came from — but it no longer feels the star's full gravity, because starlight pushes on it too.

β = F_rad / F_grav ≈ 0.57 · (Qpr/ρ) · (L*/L☉)/(M*/M☉) / s[µm]
  (Burns, Lamy & Soter 1979; ρ ≈ 1 g/cm³ icy grain, Qpr ≈ 1)

net central force  →  (1 − β)·GM*/r²
released from a circular orbit  →  eccentricity e = β / (1 − β)

Because the grain keeps its original circular-orbit speed but the effective gravity dropped, it is thrown onto a new Kepler orbit with pericenter at its birth radius. Small grains have large β (radiation pressure barely notices large grains, but dominates tiny ones): once β ≥ 0.5, e ≥ 1 and the orbit is unbound — the grain is blown out of the system on a hyperbolic trajectory. Grains just above the blowout size survive but on strongly eccentric orbits, which is what stretches real debris disks into extended dust halos far beyond the parent belt.

Grain radius slider — sets the size of dust freshly ground out of the belt (with ±20% scatter per grain, so you see a realistic mix near the threshold).
L*/M* slider — a hotter/more luminous star (or lower-mass star) pushes harder per unit grain size, raising the blowout size.
Dust production rate — how fast the collisional cascade feeds new grains into the simulation.

Watch the blowout size readout: push the grain-size slider below it and the icy dust streams away in straight, accelerating tracks instead of orbiting.

Parent belt (planetesimals) Bound dust grain (e < 1) Unbound / blown out (e ≥ 1)

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