The Observation and Research Progress on Thorne-Żytkow Objects

Recent gravitational wave detection efforts have yielded a variety of unexpected binary merger event types, revealing our ignorance regarding one of the more fundamental pillars of astrophysics–the binary evolution process. To make up for this shortfall, we have to not only rely on such rare transient events as binary mergers, but also other independent, more persistently observable inspirations. We introduce one such candidate in this review, namely the Thorne-Żytkow Objects (TŻO), that are hypothetical celestial bodies born when neutron stars sink into the centers of red giants and/or red supergiants, whose properties and inferred formation history would undoubtedly clue us in on the vitals of the progenitor binary. First, focus on the theoretical overview of the structure and evolution of massive TŻO; then focus on the observational findings of massive TŻO, especially HV2112 in the Small Magellanic Cloud; finally, summarize current related work.