ChrispenEvan said:
kip thorne has written some very accessible books for the layman.
Now he’s commented on HV 2112. See here
> When you came up with the idea of TŻOs, were you trying to explain anything that had been observed, or was it a simple “what if?” speculation?
It was totally theoretical. We weren’t the first people to ask the question either. In the mid-1930s, theoretical physicist George Gamow speculated about these kinds of objects and wondered if even our sun might have a neutron star in its core. That was soon after Caltech’s Fritz Zwicky conceived the idea of a neutron star. But Gamow never did anything quantitative with his speculations. The idea of seriously pursuing what these things might look like was due to Bohdan Paczynski, … He suggested to his postdoctoral student Anna Żytkow that she look into this idea of stars with neutron cores, and then Anna easily talked me into joining her on the project, and came to Caltech for a second postdoc. I had the expertise in relativity, and she had a lot better understanding of the astrophysics of stars than I did. So it became a very enjoyable collaboration.
> What were the properties of TŻOs as you and Żytkow theorized them?
We didn’t know in advance what they would look like, though we thought—correctly it turns out—that they would be red supergiants. Our calculations showed that if the star was heavier than about 11 suns, it would have a shell of burning material around the neutron core, a shell that would generate new elements as it burned. Convection, the circulation of hot gas inside the star, would reach right into the burning shell and carry the products of burning all the way to the surface of the star long before the burning was complete. This convection, reaching into a burning shell, was unlike anything seen in any other kind of star.
> Is this how you get different elements in TŻOs than those ordinarily seen on the surface of a star?
That’s right. We could see that the elements produced would be peculiar, but our calculations were not good enough to make this quantitative. In the 1990s, a graduate student of mine named Garrett Biehle (PhD ’93) worked out, with considerable reliability, what the products of nuclear burning would be. He predicted unusually large amounts of rubidium and molybdenum; and a bit later Philipp Podsiadlowski, Robert Cannon, and Martin Rees at the University of Cambridge showed there would also be a lot of lithium. It is excess rubidium, molybdenum, and lithium that Żytkow and her colleagues have found in HV 2112.
> Does that mean TŻOs are fairly easy to recognize with a spectrographic analysis, which can determine the elements of a star?
No, it’s not easy!
> Is there anything other than peculiar element abundances that would indicate a TŻO? Does it look different from other red supergiant stars?
TŻOs are the most highly luminous of red supergiant stars but not so much so that you could pick them out from the crowd: all red supergiants are very bright. I think the only way to identify them is through these element abundances.