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For those who don't know, "metal" doesn't actually mean metal in astronomy. They use the term to refer to any element that isn't hydrogen or helium.
by wcoenen 5y ago
For those who don't know, "metal" doesn't actually mean metal in astronomy. They use the term to refer to any element that isn't hydrogen or helium.
- leptoniscool 5y agoCorrect, since any element heavier than hydrogen or helium is created in stellar cores or from supernovas; stars that are metal-poor are either very old or formed from virgin materials from the big bang.
- akomtu 5y agoThey don't even mean elements, but spectral lines that correspond to elements if their spectrum was observed on Earth.
- astro123 5y agoThat's a weird distinction to try to make. Metal does mean the elements, not the spectral lines. The presence of those elements is usually inferred from the spectral lines, but if another method was used we would still say "metal poor/rich".
- akomtu 5y agoOther stars may as well be made of exotic particles that look like hydrogen to us.
- __alexs 5y agoDoes anti-hydrogen have the same spectral signature as regular hydrogen?
- akomtu 5y agoI guess so, if its electron/positron shell is the same. But I dont mean just antihydrogen. I'm sure there are many nucleus configurations that have the +1 charge and thus look like hydrogen from the outside.
- tryonenow 5y agoBut a larger nucleus would be unlikely to produce the same spectral signature even with the same charge. The energy transitions would be different, especially with different orbital shells and subtle quantum effects.
- bigbillheck 5y ago> I'm sure there are many nucleus configurations that have the +1 charge and thus look like hydrogen from the outside. Name three.
- TheOtherHobbes 5y agoAn anti-hydrogen star - or even an entire star system - surrounded by normal dust would show annihilation events in the spectrum. So it would be very distinctive and unusual.
- Sharlin 5y agoAnd there may just as well be an invisible dragon in my garage. There's no theory nor evidence that such exotic hydrogen impostors exist, so by Occam's razor we must assume that if it looks like hydrogen and quacks like hydrogen, it is indeed hydrogen.