Scatter plot of the specific angular momentum versus mass in the last epoch of the class I and earlier protostars. The red line is the leastsquares fit (log y = (0.90 ± 0.06) log x+ (20.8 ± 0.04)) to the data points, while the blue line is the fit to the simulated class II stars from Figure 6. The gray dotted lines are the specific angular momentum for a given disk radius (1, 100, and 10 000 au, with increasing j) as a function of stellar mass, using Eq. (29) in Padoan et al. (2025) for Keplerian disks.