Figure 30

Figure 30: The scaled growth-rate of the m = 2 instability in Newtonian disks with a dark halo (dotted line) and MONDian disks (solid line) as a function of disk mass. In the MOND case, as the disk mass decreases, the surface density decreases and the disk sinks deeper into the MOND regime. However, at very low masses the growth-rate saturates. In the equivalent Newtonian case, the rotation curve is maintained at the MOND level by supplementing the force with a round stabilizing dark halo, which causes the growth-rate to crash [77, 401]. An ad-hoc dark disk could help maintain the growth rate in the dark matter context. Image reproduced by permission from [401].