Stellar Tiramisu?

The press release from ESO compares a red giant to tiramisu—because, as Luca Pasquini puts it, “There is cocoa powder only on the top!” Hmmm.

(The cocoa powder analogy has to do with the distribution of heavy elements in stars with planets. We know that extrasolar planets are preferentially seen around stars with high iron content, but do the planets form around stars with a lot of iron distributed throughout, or do planets sprinkle iron, cocoa-like, on the stars’ surfaces?)

The image above does a bang-up job, I must say. It possesses clarity, first and foremost, comparing apples to apples and balancing the diagrammatic and the photorealistic with aplomb. I like the clear labels (with caveats to be addressed below), and the two stars even show limb darkening. Most especially, I must express my deepest appreciation for the inclusion of a small figure (in the lower right) to communicate scale! Yes! Fantastic! Super! Well done!

I would not go so far as to suggest that the diagram is flawless in its execution, however. Aside from a slight irrelevance to the topic at hand, the main liability I can detect is the inconsistency between the left- and right-hand images: “radiative zone” gets labelled only on the left, while ”burning shell” appears on the right. Something of a fumble in the home stretch…