IRAS 16293-2422B: A Compact, Possibly Isolated Protoplanetary Disk in a Class 0 Object

Abstract

Theoretical arguments suggest that protoplanetary disks around young stars should start small and grow with the addition of high angular momentum material to reach the radii of several hundred AUs that characterize the disks around optically visible T Tauri stars. Examples of much more compact disks, with radii much less than 100 AU, have been found around some very young stars, but in all cases tidal truncation from a near binary companion provides a ready explanation for the small disk size. We report here an example of a compact, possibly isolated disk around the class 0 object IRAS16293-2422B, which is thought to be among the youngest protostars known. This disk has a Gaussian half power radius of only $\sim$8 AU, and a detailed, self-consistent, accretion disk model indicates an outer radius of only 26 AU. This discovery supports the notion that protoplanetary disks start small and grow with time, although other explanations for the compact size cannot be ruled out, including gravitational instability in its outer parts and tidal truncation from the close approach of a now distant stellar companion.