Collisions of Free Floating Planets with Evolved Stars in Globular Clusters

We estimate the rate of collisions between stars and free-floating planets (FFPs) in globular clusters, in particular the collision of FFPs with red giant branch (RGB) stars. Recent dynamical simulations imply that the density of such objects could exceed million per cubic parsec near the cores of rich globular clusters. We show that in these clusters 5-10 per cents of all RGB stars near the core would suffer a collision with a FFP, and that such a collision can spin up the RGB star's envelope by an order of magnitude. In turn, the higher rotation rates may lead to enhanced mass-loss rates on the RGB, which could result in bluer horizontal branch (HB) stars. Hence, it is plausible that the presence of a large population of FFPs in a globular cluster can influence the distribution of stars on the HB of that cluster to a detectable degree.