  Spinning thermal radiation is a unique phenomenon observed in condensed
astronomical objects including the Wolf-Rayet star EZ-CMa and the red
degenerate star G99-47, due to existence of strong magnetic fields. Here, by
designing symmetry-broken metasurfaces, we demonstrate that spinning thermal
radiation with a non-vanishing optical helicity can be realized even without
applying a magnetic field. We design non-vanishing optical helicity by
engineering a dispersionless band which emits omnidirectional spinning thermal
radiation, where our design reaches 39% of the fundamental limit. Our results
firmly suggest metasurfaces can impart spin coherence in the incoherent
radiation excited by thermal fluctuations. The symmetry-based design strategy
also provides a general pathway for comprehensively controlling thermal
radiation in its temporal and spin coherence.
