Recently scientists discovered what appears to be a red supergiant star that has replaced its core with a neutron star, a combination that makes your peanut butter in my chocolate look positively bland by comparison.

A find so bizarre should have been a surprise, but it was not, at least not for astronomer Anna Zytkow. who along with theoretical astrophysicist Kip Thorne proposed the odd combo’s existence forty years ago. Zyktow and a team of collaborators now appear to have found one.

The object, called a Thorne-Zytkow object or TZO because when you make something no one had ever considered before up you get to name it, is the result of an attraction between a star that’s contracting and star that’s expanding.

Neutron stars are the cores of stars that have gone supernova and are incredibly dense and in relative terms very small. Giant stars like the red supergiant are in a phase where their gaseous envelope expands significantly. According to the TZO theory, if the neutron star is close enough to another star, like in a binary system, that it is caught by that envelope it can spiral all the way down into the giant star’s center and replace the giant’s core.

To some extent the red giant can go on, pretending it’s fine, nothing happened, it’s still the same star it always is. But having a super-dense core would make changes in the star’s fusion reactions and the elements the star produces that could be detected by spectroscopy.

After studying many stars the team thinks it has found a match, HV 2112, in the Small Magellanic Cloud.

There are some questions about the research. The star is weird, but doesn’t seem to be weird in exactly the same way as predicted in 1975, but that may only mean the theory needs to be adjusted.

“I am extremely happy that observational confirmation of our theoretical prediction has started to emerge,” Zytkow said. “Since Kip Thorne and I proposed our models of stars with neutron cores, people were not able to disprove our work. If theory is sound, experimental confirmation shows up sooner or later. So it was a matter of identification of a promising group of stars, getting telescope time, and proceeding with the project.”

[Sources:, Ars Technica]

Image: NASA Image of another red supergiant V838 Monocerotis


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