Thorne–Żytkow object

A Thorne - Żytkow object ( TZO short ) is a hypothetical star in hydrostatic equilibrium in the core of a neutron star is located. A TZO is named after the two astronomers Kip Thorne and Anna Żytkow, who gave a first description of such a star.

Neutron stars are formed mainly as a result of a supernova, which throws off the outer shell of the progenitor star. Therefore Thorne - Żytkow objects do not arise in individual stars, but only under special circumstances in binary systems. There are four developmental channels suspected:

• A red giant expanded so much that the neutron star follows its trajectory within the common sheath. Due to the friction of the neutron star decreases in the core of the red giant and ousted him. However, the neutron star would form by accretion probably as strong jets that the red giant is destroyed before the merger
• A collision of a neutron star with a massive main sequence star in a star cluster with a high stellar density
• An asymmetric supernova explosion expels the newly born neutron star to its companion in a binary star system
• Through mass exchange, the orbit reduced in an X-ray binary star consisting of a blue supergiant and a neutron star to the compact star in the atmosphere of the supergiant occurs

Thorne - Żytkow objects should be either red giants or supergiants with very special properties. Due to the neutron star at its core they reach a higher density several orders of magnitude than normal stars, which is why varying thermonuclear reactions can take place in their interior. These reactions should give rise to large amounts of lithium and elements from the r-process and p- process. However, it is not clear whether these elements are transported to the surface, where they can be detected. Let Theoretical simulations suggest that a Thorne - Żytkow object could develop into a soft gamma repeater or unusual Röntgenpulsar. For this, it is assumed that the outbreaks that eruptive stars are formed by a sporadic accretion from a fallback disk.

Alternatively, some Wolf -Rayet stars could have originated from Thorne - Żytkow objects. These special WR star would arise from red giants, where the additional nuclear reactions and released potential energy have released so much energy that a strong stellar wind has eroded the outer layers of the atmosphere of the red giant.

The life of Thorne - Żytkow objects is probably quite short, because the neutron star accretes the former core of his guest star and collapses after exceeding the Tolman -Oppenheimer - Volkoff limit into a black hole. The number of Thorne - Żytkow objects in the Milky Way should be between 20 and 200, assuming a service life of 100,000 to 1,000,000 years.

The recognized proof of a Thorne - Żytkow object has not yet succeeded. For red giants with unusual chemical abundances of 29Si and 30Si as OH359.762 0120 and U AQR it could be to TZO. But there are also stellar evolution models are conceivable in which the different chemical abundances can occur without the assumption of a TZO.

An alternative proof of the birth of a Thorne - Żytkow object could be done about gravitational waves. At the birth of a TZO waves should be emitted at frequencies between 10-5 and 0.1 Hertz, would be detected with an amplitude kpc for modern gravitational wave detectors in a radius of 10. However, this would only mean a detectable event every 500 years.