Astronomers detect almost 100 new extremely metal-poor galaxies | Hacker News Reader

Astronomers detect almost 100 new extremely metal-poor galaxies

phys.org

100 pointswglb62 comments

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

[1] https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis

Is our solar system considered metal poor?

No. I believe a metal poor solar system wouldn't have rocky planets.

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…

Here, “young” means measured from the Big Bang.

Our sun is made from the stuff of previous stars.

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.

> 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.

'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_cl...

Ah ok. So this is about the composition of just the star and not anything about the broader system.

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:

https://www.space.com/31456-rocky-planet-found-unlikely-star...

https://www.nature.com/articles/s41467-023-37195-4

That Neptune sized planet sure is close to its star. Interesting

Oh they get even bigger and closer and we've seen a bunch of those because they're more readily detectable:

https://en.wikipedia.org/wiki/Hot_Jupiter

Almost 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.

Almost pretty much the same thing really.

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.

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.”

Being able to identify both is a feat.

We have Black Sabbath, Iron Maiden, KISS, Slayer, and Megadeth. I'd say we are doing alright!

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).

Young relative to their own lifetime, old relative to us.

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.

Wait. That's an interesting statement. "Had" is the keyword which implies dual realities.

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.

If 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)

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.

[1] https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem...

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.

Who’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)

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.

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

My coffee table photobook shares a timeline of metal-poor stars:

https://impacts.to/downloads/lowres/impacts.pdf

Nice timeline. So the future is golf fields with windturbines?

Basically, how metal a galaxy is how many times a star is born, expands then collapsed as it rotates around its galaxy.

[Stub for offtopicness]

Original should say "extremely metal-poor".

Maybe they're poor and extremely-metal.

Even if they were you still wouldn't hyphenate there.

So - all the power and black metal bands in europe?

Like the Tin Man in The Wizard of Oz.

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

I was waiting for this interpretation. Alas, fixed now.

Aliens mined the metal, no other explanation.

That would argue for them being extremely old then.

There must be incredible treasures all over the galaxy. If only we could go exploring.

The treasures are built from the mind and I suppose hierarchical structures of the mind based on scarcity.

I didn't downvote you. Just want to remind people that it isn't an absolute.

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).

but only extreme metals

and money, that galaxy has no money

Cow kills man with axe

Entropy.

Ugh, that hyphenation!

Poorly written-title! They got it right in the article

> Extremely metal-poor galaxies (XMPGs) are the ones with metallicity...

Those galaxies really need more extremely-metal.

what about gpu-poor galaxies, any news?

You’re in one buddy

"Astronomers detect 95 new extremely-metal poor galaxies" would have been a better headline IMHO.

Just think of the billions of planets out there that have never heard Black Sabbath

Or the plutonium rock band Disaster Area. Long live Hotblack Desiato until taxes are due.

I came here to write that we need to put Ozzy on a spaceship and send him there to redress their lack of metal.

"My time on earth is nearly done... I am going to rock on among the stars"

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