The Kilometer Barrier: Only Large Chunks Survive from Asteroids ✛ ✦

Original: "Size limits on tidal debris around white dwarfs: the km-size barrier"

· Jordan K. Steckloff, Dimitri Veras, Kathryn Volk

arXiv:2606.02457v1 · 2026-06-01 · CC BY 4.0 · 1 min

Asteroids near white dwarfs don’t crumble to dust — they first shatter into kilometer-sized pieces.

When a star turns into a white dwarf — a super-dense remnant the size of Earth — its tidal pull rips apart passing asteroids and comets from the remnants of planetary systems. It’s like squeezing a dry cookie in your fist: it breaks into large chunks, not crumbs.

The force holding particles together keeps fragments from becoming smaller than a few hundred meters — giving rise to a “kilometer barrier.” Only after countless collisions inside a dense swarm do they gradually grind down into cosmic dust.

The fragments move almost in sync — their speeds differ by a millionth, slower than fingernail growth — so the swarm doesn’t spread out for centuries.

This dust factory explains the star’s flickering: sometimes dust eclipses it. Astronomers track this via light analysis, brightness measurements, and eclipse observations. The James Webb Space Telescope will check the details. By the way, a white dwarf can’t be heavier than 1.4 Suns — a limit discovered by Chandrasekhar.

Whole graph →

In the Solar System, sungrazing comets, as they approach the Sun, also break apart into kilometer-sized chunks — consistent with the model.

\frac{GM\rho s^4 r}{(r^2 - s^2/4)^2} = \sigma s^2 + G\rho^2 s^4

The left-hand side — the tidal force tearing apart a fragment of size s at distance r from a white dwarf of mass M; the right-hand side — the binding sum of cohesion (strength σ) and self-gravity. From this balance arises the kilometer-scale minimum size of a stable fragment.

Scientists

Enrico Fermi Paul Dirac Subrahmanyan Chandrasekhar Isaac Newton John Michell Robert Hooke

Concepts

debris disk asteroid belt Roche limit protoplanetary disk winds planetesimal formation tidal force Chandrasekhar limit dust planet tidal disruption event impact rocky planet dust dynamics snow line white dwarf schwarzschild radius gap planetary embryo mantle jupiter mass

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The Kilometer Barrier: Only Large Chunks Survive from Asteroids ✛ ✦