Accretion disks are common in space; they can form around planets, stars, and black holes. These disks play a crucial role in the formation of planets around young stars. The dynamics of an accretion disk are complex, but they essentially involve the gradual loss of angular momentum, causing material to slowly spiral inward toward the central mass. Depending on the system, this process can lead to the accretion of material onto the central object.
In the case of a young star, the accretion disk is called a protoplanetary disk.
The particles in a protoplanetary disk follow Keplerian orbits, meaning their velocity and path depend on their distance from the star. As this material orbits the star, collisions between particles create friction, which reduces their angular momentum over time. This leads to some of the material spiraling inward, while other material begins clumping together, forming planetesimals—the building blocks of planets.
An important part of understanding the formation of planets and stars, and many other objects, is modeling and complex simulations. Modern computing has enabled astrophysicists to model extraordinary complex mechanisms. Below is a simulation of the formation of a protoplanetary disk around a young star.
The animation below shows how matter spirals inward in an accretion disk.
Animation by Sam Leske
References
You can see an accretion disk in action around the star Fomalhaut, the 19th brightest star in the sky. Fomalhaut is visible from New Zealand for most of the year in the southern sky. In the Northern Hemisphere, it was considered a significant navigational star, serving as an indirect indicator of the South (MWK).
Featured image credits and links – Fomalhaut https://www.astropix.org/image/eso/potw1721a
Fomalhaut Dusty Debris Disk (MIRI Compass Image) – https://www.astropix.org/image/stsci/2023-109b
