Why do astronomers consider everything heavier than helium to be a metal?

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Why do astronomers consider everything heavier than helium to be a metal?

In: Physics
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It’s simple lazy label for ease of use.

Astronomy very, very rarely has to worry about chemical reactions, which is when we need to worry about the properties of metals.

The big thing is that hydrogen and helium make up a huge majority of what we can observe, so we need a simple catch all term for “all the rest” of the elements. And lithium is the first metallic element… So everything beyond that is lumped in as a metal. There is no real need in the field to make a finer distinction than that.

The fact that it irks chemists is a delightful bonus.

Hydrogen and Helium were made in the big bang. (maybe a little bit of lithium)

Everything else was made later by stars.

Astronomers use metal as a term for elements that were not present at the start of the universe.

Most elements *are* metals. Everything on the periodic table to the lower left of a diagonal line from Boron to Polonium is at least arguably a metal. This leaves only around ~15 out of the 90 naturally occurring elements that are definitely nonmetals, so out of ~~laziness~~ a desire for simplicity they just call all heavy-elements “metals”. Its close enough; just because we care about Carbon and Nitrogen and Oxygen more than average, doesn’t mean that the rest of the universe shares our bias.