Thorne-Zitkow
objects are a type of star that contain a neutron star core surrounded by large
envelop star such as a red giant star. Thorne-Zitkow objects were first
hypothesized by two scientists, Thorne and Zitkow in 1975. They proposed that
the star contains a neutron star of one solar mass with radius of 10 km and a
large diffuse outer layer which looks similar to a red giant star. The neutron
star and the diffuse mass was proposed to be separated by a thin, 40-meter-thick
layer where all the gravitational energy release occurred. Over decades
theories have been developed about the properties, evolution and life span of Thorne-Zitkow
objects, and also, how to find or detect them. However, research articles as
recently as 2022 describe these objects as hypothetical objects. This is
because the Thorne-Zitkow objects look similar to the red giant stars.
Martin
Rees and his group have estimated
that the birth rate of Thorne-Zitkow objects in our galaxy could be around 2×10-4
per year, i.e. one Thorne-Zitkow object can be formed in about 5000 years in our
galaxy. It has also been estimated that a Thorne-Zitkow object’s lifetime is
about a hundred thousand to one million years. Combining the formation rate and
the lifespan it is estimated that our galaxy might contains 20 to 200 Thorne-Zitkow
objects at present. The Thorne-Zitkow object phase ends when the envelop mass (red-giant
part) decreases below 14 solar masses. The envelop material may collapse down
on the neutron star which would lead to the formation of a black hole.
Certain
elements are expected to increase Thorne-Zitkow objects because of the
conditions present at the margin where the neutron star core interacts with the
outer red giant star. Dr. Levesque and her group first observed the star
(HV2112) which is situated in the Small Magellanic Cloud. They found evidence
of Rubidium, Lithium and Molybdenum elements in higher amounts than expected in
a red giant star. This observation is an indication that this star can be a Thorne-Zitkow
object. Christopher Tout’s group after just few months reiterated
this claim by citing the higher calcium content found in HV2112. Dr. Levesque
recently has also proposed that gravitational waves could be used to detect the
neutron core of the Thorne-Zitkow objects more reliably than the detection of
elements from the spectra.
In
summary, the Thorne-Zitkow objects are still postulated objects and we might
just be able to confirm their existence with new technologies.
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