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> [She] proposed in her 1925 doctoral thesis that stars were composed primarily of hydrogen and helium. Her groundbreaking conclusion was initially rejected bec
by jihadjihad 3y ago
> [She] proposed in her 1925 doctoral thesis that stars were composed primarily of hydrogen and helium. Her groundbreaking conclusion was initially rejected because it contradicted the scientific wisdom of the time, which held that there were no significant elemental differences between the Sun and Earth.
I'm reminded of a college lecture one day in a class I took called Physics of Stars. The professor walked up to the whiteboard and wrote:
Elemental composition of the universe:
Hydrogen and helium 99%
Oxygen ~1%
Everything else <<1%
That was well over a decade ago, and it blows my mind as much today as it did then.
- antognini 3y agoIn astronomy we label everything in the "Everything else" bucket as "metals." So oxygen and carbon are considered metals in astronomy. Our periodic table is quite a bit simpler.
- The_Colonel 3y agoI'm surprised there's so much oxygen ... why is that? Why isn't there more Lithium (atomic number 3) than Oxygen (8)?
- Monory 3y agoI got interested in that after your comment, and apparently there are two main reasons for that. 1. Oxygen is being produced in stars by so-called CNO cycle [0], which is how stars heavier than our sun mostly do their fusion. More intriguing question is why there's more oxygen than carbon or nitrogen (which, as implied by the name of the process, are also created), but that's a different topic. 2. Additionally, oxygen-16 is a particularly stable isotope, as its nucleus has “doubly magic” [1] amount of constituents, so it doesn't get destroyed in other processes. [0]: https://en.wikipedia.org/wiki/CNO_cycle https://en.wikipedia.org/wiki/CNO_cycle [1]: https://en.wikipedia.org/wiki/Magic_number_(physics) https://en.wikipedia.org/wiki/Magic_number_(physics)
- bobbylarrybobby 3y agoI would imagine that oxygen is at some sort of happy medium of being easy enough to create through fusion but hard enough to fuse into other things that it is unexpectedly common.