Magnetic fields strongly influence the structure and evolution of these disks. It is not possible to understand the behavior of disks at a fundamental level unless magnetism is included in the analysis from the very beginning. There are several reasons for this. Second, the primary star in a binary can sometimes be used as a probe, eclipsing portions of the disk at different times, thereby allowing disk properties to be mapped. Finally, accretion disks in eruptive binary systems are often transitory.
V is the circular rotation velocity.