Planetary formation can also be triggered by gravitational instability within the disk itself, which leads to its fragmentation into clumps. Some of them, if they are dense enough, will collapse, which can lead to rapid formation of gas giant planets and even brown dwarfs on the timescale of 1,000 years. If these clumps migrate inward as the collapse proceeds tidal forces from the star can result in a significant mass loss leaving behind a smaller body. However it is only possible in massive disks—more massive than 0.3 M ☉. In comparison, typical disk masses are 0.01–0.03 M ☉. Because the massive disks are rare, this mechanism of planet formation is thought to be infrequent. On the other hand, it may play a major role in the formation of brown dwarfs.