Editing Thorne–Żytkow object (section)

== Formation ==

A Thorne–Żytkow object would be formed when a [[neutron star]] collides with another [[star]], often a red giant or supergiant. The colliding objects can simply be wandering stars, though this is only likely to occur in extremely crowded [[globular cluster]]s. Alternatively, the neutron star could form in a [[binary star|binary system]] when one of the two stars goes [[supernova]]. Because [[Supernova#Asymmetry|no supernova is perfectly symmetric]], and because the [[binding energy]] of the binary changes with the mass lost in the supernova, the neutron star will be left with some velocity relative to its original orbit. This kick may cause its new orbit to intersect with its companion, or, if its companion is a [[main-sequence star]], it may be engulfed when its companion evolves into a red giant.<ref name=brandt95>{{cite journal |last1=Brandt |first1=W. Niel |last2=Podsiadlowski |first2=Philipp |title=The effects of high-velocity supernova kicks on the orbital properties and sky distributions of neutron-star binaries |journal=[[Monthly Notices of the Royal Astronomical Society]] |date=May 1995 |volume=274 |issue=2 |pages=461–484 |bibcode=1995MNRAS.274..461B |doi=10.1093/mnras/274.2.461 |doi-access=free |arxiv=astro-ph/9412023 |s2cid=119408422}}</ref>

Once the neutron star enters the red giant, [[drag (physics)|drag]] between the neutron star and the outer, diffuse layers of the red giant causes the binary star system's [[orbit]] to decay, and the neutron star and core of the red giant spiral inward toward one another. Depending on their initial separation, this process may take hundreds of years. When the two finally collide, the neutron star and red giant core will merge. If their combined mass exceeds the [[Tolman–Oppenheimer–Volkoff limit]], then the two will collapse into a [[black hole]]. Otherwise, the two will coalesce into a single neutron star.<ref>{{cite book |last1=Oohara |first1=Ken-ichi |last2=Nakamura |first2=Takashi |editor1-last=Evans |editor1-first=Charles R. |editor2-last=Finn |editor2-first=Lee S. |editor3-last=Hobill |editor3-first=David W. |chapter=Three dimensional initial data of numerical relativity |title=Frontiers in Numerical Relativity |date=1989 |publisher=Cambridge University Press |isbn=978-0-521-36666-3 |page=84 |chapter-url=https://books.google.com/books?id=XpzuYzu2ulsC&pg=PA84 |language=en}}</ref>

If a neutron star and a [[white dwarf]] merge, this could form a Thorne–Żytkow object with the properties of an [[R Coronae Borealis variable]].<ref name=1999ApJ...514..932V>{{cite journal |last1=Vanture |first1=Andrew | last2 = Zucker | first2 = Daniel | last3 = Wallerstein | first3 = George |title=U Aquarii a Thorne–Żytkow Object? |journal=[[The Astrophysical Journal]]|date=April 1999 |volume=514 |issue=2 |pages=932–938 |doi=10.1086/306956 |bibcode=1999ApJ...514..932V |doi-access=free }}</ref>