Collapso

Meet Collapso, a cloud of gas in space who is slowly falling in on herself to make a star.

Stars form inside cold clouds of gas and dust. If a clump becomes dense enough, its own gravity overwhelms the pressure that holds it up, and it starts to collapse. With nothing to stop it, the clump would fall to a point in a time called the free-fall time.

That time depends only on the density ρ: t_ff = √(3π/(32Gρ)). Denser clouds collapse faster. Surprisingly, the size of the cloud does not matter at all.

A typical dense core in a molecular cloud has about 10¹¹ molecules per cubic metre, a density near 4 × 10⁻¹⁶ kg/m³. Its free-fall time works out to about 100 000 years, which is quick by the standards of the galaxy.

In practice rotation, magnetic fields and heating slow things down, and a new star takes a few times longer to settle. The free-fall time is still the starting estimate astronomers use.