An accretion disc is a disc of gasses and particles that are formed in a nebula when the cloud collapses towards the center under the influence of mutual gravitation. To conserve angular momentum, the denser region spins faster and draws in the rest of the particles around it either spirally or in an orbit around it. This is known as the accretion disc. The phenomenon in which the mass accumulates at the center is called as accretion.
Frequently Asked Questions
Why is an accretion disc flat?
In any accretion disc, most particles orbit around a central point with a certain angular momentum in a flat plane. But before those particles clumped together in the same plane, there would have been particles in other planes of rotation away from the center as well. In that case, the particles would eventually collide with rest of the particles and lose its vertical momentum and energy. As there is only one direction of rotation, the particles would slowly form an orbit around the center of the massive object in a flat plane. Accretion discs inside the discs are flat too.