Capture of the free-floating planets and primordial black holes into protostellar clouds

Abstract

The capture of the free-floating planets and primordial black holes into a collapsing protostellar cloud is considered. Although the last stage of rapid contraction leading to the star formation lasts for a relatively short time $\sim 10^5$ years, during this time there is a strong change in the gravitational potential created by the movement of the entire cloud's mass ($\sim M_\odot$). As a result, the probability of capturing an object into a contracting cloud is comparable to the probability of capturing into an already formed planetary system. Taking into account the collapse of the cloud increases by 70% the full probability of the planets capture at the orbits with large semi-axis $a<10^3$ au. Capture in the cloud can explain the wide inclined orbit of the supposed 9th planet in the solar system. At the same time, the probability of primordial black holes capturing from the galactic halo into a contracting cloud is extremely small.