https://phys.org/news/2018-11-laboratory-probe-formation-stars-planets.html

Researchers at Princeton Plasma Physics Laboratory helped verify one of the proposed models for how this process works. Their work, supported by NASA, the National Science Foundation, the Department of Energy, the Simons Foundation, the Institute for Advance Study and the Kavli Institute for Theoretical Physics, will be presented at the American Physical Society Division of Plasma Physics meeting in Portland, Ore.

Typical objects orbiting a star, such as the planets going around our sun, continue orbiting for billions of years because their angular momentum remains unchanged, preventing them from falling inward. Such a system's angular momentum is a conserved quantity—it remains constant unless acted on by another force. If for some reason, the angular momentum of an orbiting object decreases, it can fall inward towards the star.