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In astronomy 'metal' is shorthand for 'all elements except hydrogen and helium' [0]. This is a convenient shorthand because big bang nucleosynthesis [1] produc
by evanb 3y ago
In astronomy 'metal' is shorthand for 'all elements except hydrogen and helium' [0]. This is a convenient shorthand because big bang nucleosynthesis [1] produces only minuscule amounts of lithium and even less heavier elements. Nonnegligible presence of elements beyond helium is indication some stars' life cycles completing and their insides being distributed via explosion. So, being metal-poor is an indicator of very young age.
[0] https://en.wikipedia.org/wiki/Metallicity https://en.wikipedia.org/wiki/Metallicity
[1] https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis
- vlovich123 3y agoIs our solar system considered metal poor?
- abainbridge 3y agoNo. I believe a metal poor solar system wouldn't have rocky planets.
- vlovich123 3y agoBut our sun is quite young afaik (middle aged) and earth is not much younger so it’s weird to hear the reasoning that metal-poor systems implies young system…
- metafunctor 3y agoHere, “young” means measured from the Big Bang. Our sun is made from the stuff of previous stars.
- codeflo 3y agoI’m assuming the poster misspoke and meant that metal-poor stars have formed when the universe was relatively young, not that the stars are young. It’s also my understanding that a planet such as ours could only have formed a bit later, after enough supernovae had formed all the carbon and iron and so on that we need to live.
- Sharlin 3y agoMaking matters confusing is the fact that the phrase "a young galaxy" is commonly used to refer to a galaxy formed when the universe was young – if it’s far away (high redshift, z >> 1) and as such we see it the way it was when the universe was young! This specific study, however, looked for more nearby galaxies (z < 1, we see the light that was emitted a few billion years ago) so these galaxies (as we see them) are in fact "old". I think essentially all existing galaxies either formed >10 Gy ago or are the results of galaxy mergers – so in that sense there are no "young", recently-formed galaxies in the universe at all as the raw material was long ago used up. As such in astro-talk "young galaxies" can fairly unambiguously mean "far-away galaxies". But formally they’d be called high-z or high-redshift galaxies.
- rbanffy 3y ago> after enough supernovae had formed all the carbon and iron and so on that we need to live. And let’s not forget some of the atoms we see around us have been through even more violent events than supernovae. Population II systems must be very boring.
- pvg 3y ago'Metallicity' in that sense is used to describe stars and the Sun, being a relatively young star is metal rich. Edit: 'young' is confusing here as pointed out in sibling comments - young compared to the age of the universe rather than young in terms of stage of stellar evolution. To make this even more confusing, this is 'population I' - younger and more metal rich unlike older, metal-poor 'population II' stars. https://en.wikipedia.org/wiki/Stellar_population#Chemical_classification_by_Baade https://en.wikipedia.org/wiki/Stellar_population#Chemical_cl...
- vlovich123 3y agoAh ok. So this is about the composition of just the star and not anything about the broader system.
- pvg 3y agoYeah although like most things in exoplanetary astronomy, the relationship between metallicity and planetary systems is an area of active research with various not-totally-intuitive findings: https://www.space.com/31456-rocky-planet-found-unlikely-star.html https://www.space.com/31456-rocky-planet-found-unlikely-star... https://www.nature.com/articles/s41467-023-37195-4 https://www.nature.com/articles/s41467-023-37195-4
- defrost 3y agoAlmost pretty much the same thing really. Consider that our sun contains 99.86% of the mass of our Solar System. Bear in mind the headline is about total spectrum of elements in entire galaxies ... eg: as in looking at our galaxy, the entire milky way, from a distance that makes it dwindle to a near point and difficult to estimate how many stars make it up. Of all the many galaxies that we can see, this is a story about a handful that are mostly hydrogen and helium .. more so than what we see as typical for galaxies.
- dudeinjapan 3y agoWe have Black Sabbath, Iron Maiden, KISS, Slayer, and Megadeth. I'd say we are doing alright!
- DiogenesKynikos 3y agoEverything you say is correct up until the last sentence. Metal-poor stars tend to be old, because the metallicity of galaxies is increasing with time (as fusion in stars and supernovae combines light elements into heavier elements).
- maxnoe 3y agoYoung relative to their own lifetime, old relative to us.
- evanb 3y agoI meant young as maxnoe suggests but you’re right obviously, a better less ambiguous thing to say is that they are from a time/place when/where no other stars have yet had the opportunity to die.
- ozfive 3y agoWait. That's an interesting statement. "Had" is the keyword which implies dual realities.
- magicalhippo 3y agoGuess a better way to phrase it is that metal-poor stars were formed long ago, relatively early after the big bang. If they're old or young depends on where in their lifecycle we observe them.
- sandworm101 3y agoNot age of the star but experiance of the material that formed the star, how many past stars was it baked in. There may be some pocket of virgin bigbang hydrogen out there that could theoretically form a new low-metal star. A low-metal/high-mass star could be a technosignature of a very advanced civilization. Nobody would dare mess with anyone capable of building themselves a new star out of only hydrogen: the ultimate keep off my lawn sign.
- LeonB 3y agoIf I were* the median atom in the universe, how many times would I have been through a full star cycle? 0? 1? 3000? * I’m not, but I’m just saying, “If I were” (but I’m not)
- anon25783 3y agoZero. Of all the atoms in the Universe, about 98% are primordial hydrogen and helium[1], "primordial" meaning they formed very shortly after the Big Bang. [1] https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...
- simonh 3y agoThat’s not quite the same question. Most of the primordial hydrogen that goes through stars isn’t fused into anything else and therefore is still primordial hydrogen, but it has been in one or more stars.
- LeonB 3y agoWho’s to say it hasn’t been through a dozen stars? Or a thousand? It could’ve blinked into existence five minutes ago. (I could be wrong)
- anon25783 3y agoHmm... I wonder what portion of all matter in the Universe is the intergalactic medium? I would conjecture that most matter in the intergalactic medium has never been inside a star.
- astroH 3y agoWhile in general, 'metal' means all elements except for hydrogen and helium, in this specific case, 'metal' really means oxygen. They are using the measurement of the [O III] 4363 line to estimate a gas temperature which allows for a determination of oxygen abundance but this gives no information on the other elements. One thing to keep in mind is that the method they use, while considered the gold-standard, is known to be biased such that metallicity is guaranteed to always be underestimated. Regardless, these galaxies are still metal-poor but it's not clear how well they mimic those in the early Universe which is one of the primary motivations for studying such objects.