Editing Thorne–Żytkow object (section)

== Properties ==

The surface of the neutron star is very hot, with temperatures exceeding 10<sup>9</sup> [[Kelvin|K]], hotter than the cores of all but the most massive stars. This heat is dominated either by [[nuclear fusion]] in the accreting gas or by compression of the gas by the neutron star's gravity.<ref name=eich89>{{cite journal | last1 = Eich | first1 = Chris | last2 = Zimmerman | first2 = Mark | last3 = Thorne | first3 = Kip | author3-link = Kip Thorne | last4 = Żytkow | first4 = Anna N. | author4-link = Anna N. Żytkow | title = Giant and supergiant stars with degenerate neutron cores | journal = [[The Astrophysical Journal]] | date = November 1989 | volume = 346 | issue = 1 | pages = 277–283 | doi = 10.1086/168008 | bibcode = 1989ApJ...346..277E }}</ref><ref name=cannon92>{{cite journal |last1=Cannon |first1=Robert |last2=Eggleton |first2=Peter |last3=Żytkow |first3=Anna N. |author3-link=Anna N. Żytkow |last4=Podsialowsky |first4=Philipp |title=The structure and evolution of Thorne-Zytkow objects |journal=[[The Astrophysical Journal]] |date=February 1992 |volume=386 |issue=1 |pages=206–214 |doi=10.1086/171006 |bibcode=1992ApJ...386..206C |doi-access=free }}</ref> Because of the high temperature, unusual nuclear processes may take place as the envelope of the red giant falls onto the neutron star's surface. [[Hydrogen]] may fuse to produce a different mixture of [[isotope]]s than it does in ordinary [[stellar nucleosynthesis]], and some astronomers have proposed that the [[Rp-process|rapid proton nucleosynthesis]] that occurs in X-ray bursts also takes place inside Thorne–Żytkow objects.<ref name=cannon93>{{cite journal |last=Cannon |first=Robert |title=Massive Thorne–Żytkow Objects – Structure and Nucleosynthesis |journal=[[Monthly Notices of the Royal Astronomical Society]] |date=August 1993 |volume=263 |issue=4 |pages=817–838 |bibcode=1993MNRAS.263..817C |doi=10.1093/mnras/263.4.817 |doi-access=free }}</ref>

Observationally, a Thorne–Żytkow object may resemble a [[red supergiant]],<ref name=levesque/> or, if it is hot enough to blow off the hydrogen-rich surface layers, a nitrogen-rich [[Wolf–Rayet star]] (type WN8).<ref>{{cite conference |title=Are Peculiar Wolf-Rayet Stars of Type WN8 Thorne-Zytkow Objects? |first1=Cedric |last1=Foellmi |first2=Anthony F. J. |last2=Moffat |bibcode=2002ASPC..263..123F |arxiv=astro-ph/0607217 |date=2002 |isbn=1-58381-103-6 |book-title=Stellar Collisions, Mergers and their Consequences |conference=ASP Conference Proceedings |volume=263 |editor-first=Michael M. |editor-last=Shara }}</ref>

A TŻO has an estimated lifespan of 10<sup>5</sup>–10<sup>6</sup> years. Given this lifespan, it is possible that between 20 and 200 Thorne-Żytkow objects currently exist in the [[Milky Way]].<ref>{{Cite journal |last1=Podsiadlowski |first1=Philipp |last2=Cannon |first2=Robert C. |last3=Rees |first3=Martin J. |date=May 1995 |title=The evolution and final fate of massive Thorne-Żytkow objects |url=http://adsbit.harvard.edu/full/1995MNRAS.274..485P |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=274 |issue=2 |pages=485–490 |bibcode=1995MNRAS.274..485P |doi=10.1093/mnras/274.2.485 |doi-access=free}}</ref>

The only way to unambiguously determine whether or not a star is a TŻO is a multi-messenger detection of both the [[gravitational waves]] of the inner neutron star and an optical spectrum of the metals atypical of a normal [[red supergiant]]. It is possible to detect pre-existing TŻOs with current [[LIGO]] detectors; the neutron star core would emit a continuous wave.<ref>{{Cite journal |last1=DeMarchi |first1=Lindsay |last2=Sanders |first2=Jax R. |last3=Levesque |first3=Emily M. |date=Apr 2021 |title=Prospects for Multimessenger Observations of Thorne-Żytkow Objects |journal=[[The Astrophysical Journal]] |volume=911 |issue=2 |pages=101 |bibcode=2021ApJ...911..101D |doi=10.3847/1538-4357/abebe1 |arxiv=2103.03887 |doi-access=free }}</ref>