Protoplanetary disk

A rotating disk of gas and dust surrounding a young star. Its material can aggregate into planetesimals and, eventually, planets.

Dust coagulation: The sticking and growth of dust grains through collisions. Collisions can turn microscopic disk grains into larger aggregates.
Keplerian disk: A rotating disk in which orbital motion is primarily governed by a central body's gravity. Most of the disk's orbital motion is organized around the young star.
ALMA: The Atacama Large Millimeter/submillimeter Array, a radio observatory in Chile. Its high-resolution images reveal rings, gaps, and dust in nearby disks.
Disk substructure: Rings, gaps, spirals, and other departures from a smooth disk distribution. Some structures may trace planets, but several processes can produce similar patterns.
Streaming instability: A process in which interactions between gas and drifting solid particles concentrate solids into dense clumps. Dense clumps can collapse gravitationally into planetesimals.
Angular momentum transport: The redistribution of angular momentum that allows material in a rotating system to move inward or outward. It enables disk gas to accrete onto the star while other material spreads outward.
Spectral energy distribution: A representation of an object's emitted energy across a range of wavelengths. Infrared excess in a young star's spectrum can signal a surrounding disk.
Planet migration: The change in a planet's orbit caused by interactions with its surroundings. Disk-driven migration can reshape where planets end up before the gas disappears.
Planetesimal: A small solid body formed from dust and ice that can combine with others to build planets. It is a key intermediate between disk grains and planets.
Interstellar medium: The gas and dust occupying the space between stars in a galaxy. A young star and its disk form from collapsing interstellar material.

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