On energetics and progenitors of odd radio circles: a causal connection with tidal disruption of stars?

Abstract

Odd Radio Circles or ORCs are recently discovered edge-brightened, low surface brightness circular radio sources. The progenitors and astrophysical processes responsible for their origins are presently debated. Some ORCs are host-less and some appear to be hosted in distant quiescent galaxies. Two plausible explanations consider ORCs as nearby supernova remnants with sizes a few hundred parsec in the intragroup medium of the Local Group of galaxies or alternatively shocked haloes of a few hundred kpc extent around distant galaxies. The input shock energy required to create ORCs of a few hundred kpc size is estimated in a range of 1055–1059 erg. It is shown here that the cumulative energy in unbound debris ejected from multiple (105–109) tidal disruption events over ∼100 Myr period around a central massive black hole can meet the required energies to generate ORCs around some galaxies, which have recently undergone a merger. The potential hosts for ORCs are identified here as abundant post-starburst galaxies at intermediate redshifts having massive black holes. A causal connection between ORC around quiescent galaxies and tidal disruption may find support in the observed dominance of tidal disruption events in post-starburst galaxies.