Effects of suprathermal grains

Grains ejected from stars at velocities of ~ 10⁷ cm s^-1 and/or grains accelerated by the pressure of starlight in the intercloud medium to velocities in the range 2×10⁶–10⁷ cm s^-1 are slowed to velocities of about 2×10⁵ cm s^-1 in a typical interstellar cloud. The interaction of fast grains with gas atoms as they are slowed in clouds could provide (a) the dominant heat source for interstellar clouds; (b) sites for molecule formation; and (c) a mechanism of providing a pressure balance between clouds and the intercloud medium.