Attractive Optical Forces from Blackbody Radiation

TL;DR

This paper demonstrates that blackbody radiation can exert an attractive optical force on atoms, which can surpass gravity and influence astrophysical phenomena, especially around hot objects.

Contribution

It explicitly calculates the attractive blackbody optical dipole force on hydrogen atoms, revealing it can dominate gravity and affect astrophysical environments.

Findings

Blackbody radiation induces an attractive force on atoms.

This force can exceed gravitational pull on hydrogen.

The effect is relevant in astrophysical contexts with hot dust.

Abstract

Blackbody radiation around hot objects induces ac Stark shifts of the energy levels of nearby atoms and molecules. These shifts are roughly proportional to the fourth power of the temperature and induce a force decaying with the third power of the distance from the object. We explicitly calculate the resulting attractive blackbody optical dipole force for ground state hydrogen atoms. Surprisingly, this force can surpass the repulsive radiation pressure and actually pull the atoms against the radiation energy flow towards the surface with a force stronger than gravity. We exemplify the dominance of the "blackbody force" over gravity for hydrogen in a cloud of hot dust particles. This overlooked force appears relevant in various astrophysical scenarios, in particular, since analogous results hold for a wide class of other broadband radiation sources.