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.
But 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…
I’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.
Making 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.
'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.
Yeah 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:
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.
Given our sun is a population I or heavy-element-rich star that'd almost certainly be the case ... the elements that didn't fall into our sun to make it so remained in orbit and are also heavy element rich (obviously relatively more so that the mostly H-He sun).
A Sun sized metal poor star wouldn't be surrounded by large amounts of orbiting heavy elements .. that would suggest even larger amounts failed to orbit and fell into that star.
( I'll freely confess to being decades out of date on the conjectured life of stars though, these days I mainly do geophysics related to astrophysics (cancelling out ground effects from SKA type projects) )
Oh I just meant that amount of metal for some (entirely made up) stars would already be pretty metal. The sort of astro out of an Asimov joke story.
But as the black hole approached, Hieronymus noted there was no gravitational effect. He studied it more closely and announced, with a chuckle, that it was not a black hole after all.
“It’s nothing,” he said. “Just an ordinary asteroid someone has painted black.”
Everything 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).
I 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.
Guess 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.
Not 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.
Zero. 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.
That’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.
Hmm... 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.
Most of the universe is primordial atoms that haven’t fused yet but if you were to take an iron atom, it probably would have been through only one star cycle.
A main sequence star at least ten times the size of the sun goes through several stages as it ages: hydrogen, helium, carbon, neon, oxygen, and finally silicon burning. The silicon burning stage produces abundant iron and the type II supernova that follows spreads it around.
Such a civilization wouldn't have much incentive to build 'keep off my lawn' signs, I don't think, given that the answer to such an advertisement should be a trillion relativistic snowflakes aimed at every system within a thousand lightyears. Anyone observing such a show of power would have no choice but to act first before that civilization did it to them.
While 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.
Honestly I considered this interpretation for far too long - "extremely-metal" but poor. Now what that means I don't know, but I thought it might have related to something an astronomer could tell me
This is a fascinating thing to consider - humans are either boring because there's aliens all over the place, or we're pretty much unique because life is incredibly rare.
If we're not unique then it doesn't really matter if we wipe our species out. We'll just get chalked up to the great filter and some other species will do some archeology on Earth in the future.
I find the idea that we're unique much more interesting. If we are then we're effectively the guardians of the only intelligent life in the universe, and we should be doing a lot more to preserve it. Maybe there aren't treasures all over the universe. Maybe they're all here on our planet (and a few on the moon and Mars).
A really beautiful book about the subject is Anna Frebel's "Searching for the Oldest Stars". One of the best books I've read on popular science in the last few years. I am in awe of what we can understand looking at those objects
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[ 1.8 ms ] story [ 133 ms ] thread[0] https://en.wikipedia.org/wiki/Metallicity
[1] https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis
Our sun is made from the stuff of previous stars.
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.
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.
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_cl...
https://www.space.com/31456-rocky-planet-found-unlikely-star...
https://www.nature.com/articles/s41467-023-37195-4
https://en.wikipedia.org/wiki/Hot_Jupiter
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.
Consider that our sun contains 99.86% of the mass of our Solar System.
If you dumped that into a Sun-sized metal-poor star, it would probably pass for metal-rich.
A Sun sized metal poor star wouldn't be surrounded by large amounts of orbiting heavy elements .. that would suggest even larger amounts failed to orbit and fell into that star.
( I'll freely confess to being decades out of date on the conjectured life of stars though, these days I mainly do geophysics related to astrophysics (cancelling out ground effects from SKA type projects) )
But as the black hole approached, Hieronymus noted there was no gravitational effect. He studied it more closely and announced, with a chuckle, that it was not a black hole after all.
“It’s nothing,” he said. “Just an ordinary asteroid someone has painted black.”
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.
* I’m not, but I’m just saying, “If I were” (but I’m not)
[1] https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...
(I could be wrong)
A main sequence star at least ten times the size of the sun goes through several stages as it ages: hydrogen, helium, carbon, neon, oxygen, and finally silicon burning. The silicon burning stage produces abundant iron and the type II supernova that follows spreads it around.
https://impacts.to/downloads/lowres/impacts.pdf
I didn't downvote you. Just want to remind people that it isn't an absolute.
If we're not unique then it doesn't really matter if we wipe our species out. We'll just get chalked up to the great filter and some other species will do some archeology on Earth in the future.
I find the idea that we're unique much more interesting. If we are then we're effectively the guardians of the only intelligent life in the universe, and we should be doing a lot more to preserve it. Maybe there aren't treasures all over the universe. Maybe they're all here on our planet (and a few on the moon and Mars).
and money, that galaxy has no money
> Extremely metal-poor galaxies (XMPGs) are the ones with metallicity...
"My time on earth is nearly done... I am going to rock on among the stars"