We study the solar emission of light dark sector particles that self-interact strongly enough to self-thermalize. The resulting outflow behaves like a fluid which accelerates under its own thermal pressure to highly relativistic bulk velocities in the solar system. Compared to the ordinary noninteracting scenario, the local outflow has at least $\sim {10}^3$ higher number density and correspondingly at least $\sim {10}^3$ lower average energy per particle. We show how this generic phenomenon arises in a dark sector composed of millicharged particles strongly self-interacting via a dark photon. The millicharged plasma wind emerging in this model has novel yet predictive signatures that encourages new experimental directions. This phenomenon demonstrates how a small step away from the simplest models can lead to radically different outcomes and thus motivates a broader search for dark sector particles.

• Received 14 June 2022
• Revised 19 October 2022
• Accepted 19 October 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.211101

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society