Free Astronomy Magazine September-October 2014

35 STELLAR EVOLUTION SEPTEMBER-OCTOBER 2014 What would happen if a neutron star sank into a red su- pergiant right down to its core? Apparently nothing, but in that extreme environment it would start off an atypi- cal thermonuclear engine which would confer to the su- pergiant atmosphere a rather unusual composition. ry first ow object I n the last few centuries, astronomers and theoretical physicists have on many occa- sions predicted the existence of celestial bodies well in advance of their actual dis- covery. The last case is very recent and con- cerns Thorne- Ż ytkow objects, (T Ż Os) the existence of which seems to have been fi- nally ascertained, nearly 40 years after the model that predicts their existence had been formulated. In fact, it was between 1975 and 1977 that Kip Thorne and Anna Ż ytkow theoretically studied a star formed by the union of two stars very different from each other, a red supergiant and a neutron star. At the time it didn't seem much more than a mathematical curiosity and we were still far from being able to ver- ify by direct observation the existence of such exotic celestial bodies. This is mainly because T Ż Os look much like red super- T he illustra- tion in the back- ground is an art- ist's impression of the explosion of a supernova, as a result of the fall on a degen- erate star of mat- ter from a red supergiant. From a scenario similar to this it is possi- ble to arrive at the formation of a Thorne- Ż ytkow object, as long as the collapsed star, remnant of the supernova, merges with the core of the red supergiant. [David Hardy]