Disk Dispersal around Young Stars

. o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o We review the evidence pertaining t the lifetimes f planet-f rming disks and discuss p ssible disk dispersal mechanisms: (1) visc us accreti n f material nt the central s urce, (2) cl se stellar enc unters, (3) stellar winds, and (4) ph t evap rati n by ultravi let radiati n. We f cus n (3) and (4) and describe the quasi-steadystate appearance and the verall ev luti n f disks under the influence f winds and radiati n fr m the central star and f radiati n fr m external OB stars. Visc us accreti n likely d minates disk dispersal in the inner disk ( 10 AU), whereas ph t evap rati n is the principal pr cess f disk dispersal utside f 10 AU. Disk dispersal timescales are c mpared and discussed in relati n t the retical estimates f r planet f rmati n timescales. Ph t evap rati n may explain the large differences in the hydr gen c ntent f the giant planets in the s lar system. The c mm nly held belief that ur early sun’s stellar wind dispersed the s lar nebula is called int questi n.