A relic from the primitive Universe... in our own backyard!

"We have been forced to admit for the first time in history not only the possibility of the fact of the growth and decay of the elements of matter. With radium and with uranium we do not see anything but the decay. And yet, somewhere, somehow, it is almost certain that these elements must be continuously forming. They are probably being put together now in the laboratory of the stars." -Robert Millikan

The Universe has been around for a long time, but without the Big Bang, we'd never have any of the matter or starlight that gives rise to practically all of our experiences in the entire Universe.

Image credit: NASA / WMAP science team.

13.7 billion years ago -- minus one microsecond -- the Universe was filled with protons, neutrons, neutrinos and photons, and electrons and positrons. The temperatures were high enough that heavier elements could be fused together in this hot, dense crucible, but there were too many high-energy particles for them to remain; they were blasted apart almost instantaneously. By time the Universe had cooled enough so that the first heavy combination of these particles -- a deuteron -- would be stable, the Universe was over three minutes old, and the density had dropped by a factor of around a billion.

Protons and neutrons then fuse together furiously, building up heavy elements as best as they can, but because the expanding Universe is now so much sparser and cooler, it can only form deuterium, helium, lithium and beryllium; all the heavier elements are out of reach.

Image credit: Ned Wright's cosmology tutorial; data from Burles, Nollett & Turner (1999).

This process -- known as Big Bang Nucleosynthesis -- accounts for the lightest elements in the Universe, and is where all the matter today eventually comes from.

Yes, that's right: all of it. Including things like you and me, made primarily out of carbon, oxygen, hydrogen and nitrogen, where most of the elements in our body did not exist at the beginning of the Universe. In order to create them -- in fact, in order to create nearly all of the elements on our planet -- it took generations of stars burning through their nuclear fuel, fusing light elements into heavier ones, and recycling those elements back into the interstellar medium to form new and subsequent generations of stars, now enriched with these heavy elements.

Image credit: NASA, ESA, SSC, CXC, and STScI.

But this means that one of the great predictions of the Big Bang is that -- if we're fortunate enough -- we can find some of this pristine gas, direct from the primordial Universe. Atoms that have never been inside of a star before; that have never been burned inside of a nuclear furnace, that have never been spit back out into the cosmos to light the next generation.

This is very difficult, of course, because stars form all over the Universe, and finding "unpolluted" regions should be extremely rare, and should only become increasingly rare as we come forward in time.

Image credit: NASA.

Last year, we got incredibly lucky. There's a technique we have, where we look very far back in the Universe, where we not only see the light from the extremely distant object we're observing, but we also see the absorption lines from anything between that distant object and ourselves.

This makes it possible -- in principle, at least -- to find a cloud of gas that has not yet collapsed to form any stars, so long as there's a region of space behind it that has.

Image credit: NASA / STScI.

In a stroke of serendipity, last year we discovered two such clouds that appear to have the exact abundances of Hydrogen and Helium predicted by Big Bang Nucleosynthesis, and none of the heavier elements that would exist in gas that was polluted by prior generations of stars. These two clouds, labelled with green arrows in the image below, are the most pristine clouds of gas -- and they're totally star-free -- we've ever found.

Image credit: M. Fumagalli, J.M. O'Meara, & J.X. Prochaska; http://arxiv.org/abs/1111.2334.

That "Z" on the y-axis is astronomer shorthand for "elements heavier than hydrogen and helium," more formally known as metallicity. (Why? Because "X" is Hydrogen, "Y" is Helium, and "Z" is everything else combined. I know, I know, carbon, nitrogen, oxygen, etc., are not metals. To you. But they are to an astronomer; just roll with it.) So these intergalactic clouds are the most metal-free clouds we've ever found.

But what about stars? Sure, due to the way light becomes harder and harder to observe the more distant objects become, we're really restricted to our own galaxy and the very nearby vicinity (e.g., globular clusters) if we want to measure an individual star. But we've found some very, very metal-poor stars, and I want to share with you the current record-holder.

Image credit: ESO / Digitized Sky Survey 2.

This completely non-descript star, SDSS J102915+172927 (or, in plain english, Caffau's star), was found by the Sloan Digital Sky Survey last year. While pretty much every other star we've ever found -- from the metal-rich to the metal-poor -- has some amount of lithium and carbon in it, this star is pretty much all hydrogen and helium.

How much is "pretty much?"

Image credit: ESO / Digitized Sky Survey 2.

It's the most pristine star ever discovered, and it couldn't have formed the way stars normally formed; in order to do so, stars need to cool, and it's thought to take metals to do that conventionally. If you want to form stars the way the first stars in the Universe were formed, you need some type of special cooling, such as through dust.

But just because science doesn't understand all the details of how a star like this got to be here doesn't mean this isn't an amazing story: some star had to be the first to form in the Universe, and our best estimates are that if the Universe is 13.73 billion years old now, the first stars formed when it was maybe 13.68 billion years old. And this star definitely exists with the properties just described; figuring out exactly how it formed could be a window into the earliest of times in the Universe!

Image credit: NASA / WMAP.

The paper announcing the discovery of the most metal-free star ever discovered is here, and it's amazing how untouched a star can be after over 13 billion years in our galaxy. The star is at least 13 billion years old, has the mass of about 80% of the Sun (making it a K-type star), and fortunately, it won't be alone for long. The team that found it expects to find five-to-fifty more stars just like it over the next decade using the same technique!

So say hello to the primitive Universe; a piece of it is right in our own backyard!

More like this

Wow..Great and to be honest Quite a surprise to hear this one..

Must admit..nothing short of End of Year Gift..!!!

By Arnab Roy (not verified) on 26 Dec 2012 #permalink

Hi Ethan,

a question... you wrote: " and it couldn’t have formed the way stars normally formed; in order to do so, stars need to cool"

I haven't came across this before, and couldn't find anything on wiki about it. Could you explain this "cooling" a bit more, or point to some article. Thank you. :)

By Sinisa Lazarek (not verified) on 26 Dec 2012 #permalink

Sinisa: the basic idea of "cooling" goes like this: when a cloud of gas and dust starts to collapse due gravity, the particles fall inward. As they fall, they pick up kinetic energy, so each particle moves faster as it bumps into its neighbors. Faster speeds of the particles means that the temperature of the gas rises.

Now, if the temperature remained high, the cloud would not be able to collapse far enough to form a dense core and create a star. The motions of all the particles would push outward, halting the collapse.

However, if the atoms and molecules can radiate away energy after they bump into their neighbors, and that radiation can escape from the cloud out into space, then the atoms and molecules can lose their kinetic energy and slow down. The ability of a cloud of gas to radiate away its kinetic energy is crucial for it to collapse enough to form a star.

It turns out that atoms of hydrogen and helium are not very good at turning kinetic energy into radiation. When these atoms bump into each other at the speeds typical for a collapsing cloud, they don't easily reach the excited states necessary to radiate energy ... and, on top of that, any photons they radiate will very likely be re-absorbed by other atoms of hydrogen and helium nearby.

On the other hand, atoms such as carbon and oxygen can turn kinetic energy into radiation efficiently, _and_ the photons they radiate are more likely to escape into space than those from hydrogen and helium. So, if a cloud of gas contains even a small amount of these heavier elements, it is much more likely to collapse into a dense core than if it is pure (or nearly pure) hydrogen and helium.

In short, a small sprinkling of heavy elements acts to cool a cloud of gas.

By Michael Richmond (not verified) on 27 Dec 2012 #permalink

"Faster speeds of the particles means that the temperature of the gas rises."

Only when the energies of the particles have been "thermalised".

The compact flourescent light bulb gives a light similar to the light of an incandescent bulb at 3500C yet the flourescent bulb is easily held in the hand and fairly cool.

Because the medium is not in thermal equilibrium: the flourescent material is optically thin.

Similarly the collisions in the collapsing gas cloud must be at least vaguely in some statistically significant equilibrium to be accorded a temperature.

Not radiating well means the H and He gain energy quicker than it loses it until it reaches an excited state and then the medium can radiate much quicker. And it will only be absorbed in a thick or similarly excited medium (which will then radiate itself as quickly as before).

Heavier elements may help speed the increase in a stars' weight gain and may therefore increase the number of multiple star systems but I don't know that it speeds the collapse by more than a few percent.

" Caffau's star is a population II star in the galactic halo, seen in the constellation Leo. It is about 13 billion years old, making it one of the oldest stars in the Galaxy. At the time of its discovery, it had the lowest metallicity of any known star."

So Nice, but Caffau is a population II star not a population III star.

" Population III stars should only be seen in faraway galaxies whose light originated much earlier in the history of the universe, and searching for these stars or establishing their nonexistence (thereby invalidating the current model) is an active area of research in astronomy... Detection of populations III stars is a goal of NASA's James Webb Space Telescope. New spectroscopic surveys, such as SEGUE or SDSS-II, may also locate Population III stars."

Back to Caffau's star.
"John Norris of the Australian National University, who wrote a commentary in Nature on the new discovery. "I go out and measure things. It doesn't bother me if it goes against existing theories. It's the theorists' job to explain what I see." He admits that he finds the lack of lithium in Caffau's star "really puzzling" and has no clear explanation for it, but he does have thoughts about the carbon-oxygen problem." http://www.time.com/time/health/article/0,8599,2092027,00.html

This Sept 2011 paper is very interesting.
The full pdf takes a while to load, but does load: http://www.eso.org/public/archives/releases/sciencepapers/eso1132/eso11…

This is NOT a metal free star, i.e. not a population III star. As Elisabetta Caffau lead author for whom Caffau's star is named says, "“But to explain the presence of a small amount of metals, it has been formed from material contaminated by the ejection of at least one massive star. Therefore it is at least a second generation star."

Hmm, interesting but I'll wait for James Webb for further clarification .

"So Nice, but Caffau is a population II star not a population III star."

Well, there would be some metals in the earliest condensed material in the universe created in the disassociation of matter and energy.

It'd be practically impossible to call a star with zero metals.

I guess you have the same problem as saying "when does the child become an adult?". Just define it and be done with it.

Metallicity won't tell you.

If there hasn't been enough time for any star to concievably go nova before the target star before it formed, you have your pop 3.

Problem is that only gives you a few million years to play with.

"To detect the signature of the “first light” sources in the early Universe i.e. Population iii stars (see, e.g., Figure 1). SIMPLE will provide high S/N, high resolution absorption spectra of QSOs and GRBs at, or beyond, the reionisation epoch, thus tracing the early chemical enrichment and dust content
of proto-galaxies along their line of sight."

"Targets (mostly QSOs at z > 6.5) will be provided by ongoing and planned NIR surveys (VISTA, PanSTARRS, Euclid/SNAP).
While SIMPLE will be unique in detecting the chemical fingerprint of the first light galaxies in absorption, JWST and other ELT instruments (HARMONI and EAGLE) will provide
complementary information by searching for Population iii signatures in emission"

"From our direct experience with ISAAC, extrapolated to X-SHOOTER which has a better eciency, we estimate that with a 4 hour long exposure, it would possible to detect an emission line with a ux greater than 1:10^-17 ergs/s/cm2 (S/N=5), which is in the range of the spectroscopically conrmed LAEs. It is also clear that the spectral resolutions of X-SHOOTER is ideally adapted to provide good coverage of the UV restframe spectrum allowing in particular to search for possible emission features of population III stars such as HeII. (Helium II)"

"The detailed analysis of the faint light from two of the most distant galaxies we found suggests that the very first generation of stars may have contributed to the energy output observed," says Eros Vanzella of the INAF Trieste Observatory, a member of the research team. "These would have been very young and massive stars, about five thousand times younger and one hundred times more massive than the Sun, and they may have been able to dissolve the primordial fog and make it transparent.""

"The highly accurate measurements required to confirm or disprove this hypothesis, and show that the stars can produce the required energy, require observations from space, or from ESO’s planned European Extremely Large Telescope, which will be the world’s largest eye on the sky once completed early next decade."

my original comment here was destroyed. I've no time to re-create it. But the above quotes make the point that the ESO Team is very active in observing the very early universe and other quotes suggest that they believe that observing first generation stars (i.e. population III stars) is technically possible and will be done in the next decade. Assuming that current theories about population III stars hold correct.

I wish I could find my original comment but it got lost in a glitch as i submitted it. Cheers.

"ESO Team is very active in observing the very early universe and other quotes suggest that they believe that observing first generation stars (i.e. population III stars) is technically possible and will be done in the next decade."

Not disagreeing, but saying that the star has heavier elements isn't going to tell you that it's a population II star isn't the same thing.

shouldnt the initial big bang expansion representation be more spherical rather than bell shape

By lilbear68 (not verified) on 28 Dec 2012 #permalink

it's a picture of the cross-section.

Width of the funnel is the size of the universe and the length of it is time progressing.

If we accept the big bang theory; then we need to be willing to test it again and again with harder test. In my mind one important milestone test will be the finding of population III, i.e. first generation stars., not in the milky way but in the most distant galaxies. I can wait a decade or few.

Caffau's particular population II star is very interesting but it also creates some puzzles.
1) why is it so lithium poor
2) Ethan refers to this as "the most metal-free star ever discoveredt" But according to ESO site.
-----a) the proportion of metals in SDSS J102915+172927 is more than 20 000 times smaller than that of the Sun BUT
-----b) a star like HE 0107-5240, with about 0.8 solar mass and 1/200,000 of the metal content of the Sun
3) So why is this star such an interesting population II star?
----- a) Caffau's star (J102915+172927)is at the edge of the visible universe so it's properties are presummably nearer to hypothesized population III stars. And if we can observe Caffau; then we should be able to observe population III stars. Here I must note that there are two entirely different types of population III stars. (Maybe?)Here I am talking about the first type, the very massive metal free stars predicted by the big bang. And it is this type of population III (i.e. ") the ones which form out of the pristine gas left over after cosmological nucleosynthesis and generate the first metals")that Caffau's star give hope that the ESO team can find. Good let them find them or NOT and then modifiy their the theory appropriate to what is observed.
-----b) HE 0107-5240 on the other hand is not a very ancient observation, it is part of our own Milky Way galaxy ( at a distance of about 36,000 light-years.) it is also very old star, with an age of roughly 13 billion years.. So even though it is more metal poor than Caffau it is technically not as interesting. But it does relate to the 2nd type of population III stars )maybe?) (i.e. "the ones which have been hypothesized to provide the dark matter in galactic halos"), which should form in the halo's of galaxies like the mikly way. "spectroscopic observations - which are necessarily quite time-consuming - have only been made of about one-quarter of the 8000 low-metal-abundance candidate stars identified in that survey. It is therefore not excluded that a bona-fide Population III star may eventually be found in the course of this programme."

"The discovery of HE 0107-5240 in the Milky Way's halo demonstrated that stars that are less massive than Sol can form from very metal-poor gas. This finding was unexpected, as most current theoretical calculations indicate that it should have been very difficult to form low-mass stars shortly after the Big Bang because heavier elements are needed to efficiently cool gas clouds as they contract into stars (see discussion on the expected mass of Population III stars from Bernard Carr, 1994 versus Richard B. Larson, 1999). However, the existence of HE 0107-5240 suggests that there must be other ways of achieving the necessary cooling. Moreover, the star's discovery suggests to some astronomers that even relatively low-mass Population III stars could have formed and survived until today, still shining faintly below easy detectability as main sequence dwarf stars in distant reaches of the galactic halo."

So ESO astronomers are looking for both types of population III stars; and I think we own these scientists the courtesy to wait and see what they observe. And then wait and see what the theorist conclude from their observations.

Now back to Caffau's star, " the ESO team found that the proportion of lithium in the star was at least fifty times less than expected in the material produced by the Big Bang. “It is a mystery how the lithium that formed just after the beginning of the Universe was destroyed in this star.”.. The researchers also point out that this freakish star is probably not unique. “We have identified several more candidate stars that might have metal levels similar to, or even lower than, those in SDSS J102915+172927. We are now planning to observe them with the VLT to see if this is the case,” concludes Caffau. "

Essentially everything above and below is copied from a calteck site, the eso site or wikipedia, or etc..

HE1327-2326, is the star with the lowest known iron abundance to date. The star is a member of Population II, with an iron to hydrogen ratio ([Fe/H]), or metallicity, of -5.6. This number indicates that its iron content is 400,000 times less than that of the Earth's sun. It is 4000 lightyears away.

"In my mind one important milestone test will be the finding of population III, i.e. first generation stars."

I don't know that this is any proof whatsoever of a big bang.

All Pop3 stars need is some time when star formation didn't occur. That doesn't have to be because of a universe being created but could be from a collapsing one for example.

The big bang theory is merely the consequence of the observation that the universe is expanding isotropically and therefore if you run time backward the entire universe would have been at one point.

There really isn't any more to the proof of the situation than that.

Any competing theory would have to better explain the movement withough putting forward a force or mechanism that we have no evidence for (therefore you must prove that mechanism with independent evidence first).

I.e. if you wanted to say "God made them move apart to give us more room", you need to find some proof of god other than "well, the universe is expanding, which god did, therefore that proves he exists!".

Predictions have meanings.

Population III stars are an important predicition. i.e. first generation stars. If we are technically able to observe them and find them or NOT; then theory is affirmed or NOT.

Just so dark matter, or gravitational waves, or Michelson Morley's aether. If we find them then theory is affirmed; if NOT then theory needs to at least be modified.

The theory goes " the fact that all stars observed have some heavier elements poses something of a puzzle, and the current explanation for this proposes the existence of hypothetical metal-free Population III stars in the early universe. Soon after the Big Bang, without metals, it is believed that only stars with masses hundreds of times that of the Sun could be formed; near the end of their lives these stars would have created the first 26 elements up to iron in the periodic table via nucleosynthesis.[3]
Because of their high mass, current stellar models show that Population III stars would have soon exhausted their fuel and exploded in extremely energetic pair-instability supernovae. Those explosions would have thoroughly dispersed their material, ejecting metals throughout the universe to be incorporated into the later generations of stars that are observed today... Population III, or metal-free stars is a hypothetical extinct population of extremely massive and hot stars with virtually no surface metals, except for a small quantity of metals formed in the Big Bang, such as lithium-7."

Very nice explanation. And we've got ESO scientist technically capable of observing these population III stars in the next decade or so. As well, "Detection of populations III stars is a goal of NASA's James Webb Space Telescope. New spectroscopic surveys, such as SEGUE or SDSS-II, may also locate Population III stars."

Most scientist assert that hypothesized "metal producing... producing Population III stars.. must exist." There is more debate about the existence or NOT of other types of population III stars.

Well let's wait and see what we find. I for one expect to see some new science from better understanding of:
- population III stars
- dark matter
- extradimensions
- eternal inflation
- etc.

It is very unclear to me how much new science will result from better understanding these key concepts. Theorist have done a lot of excellent work (often that conflicts with one andothers assumptioon). The only way to decide which theories are b est is to achieve better data from experiment and observation.

The problem is not "saying “when does the child become an adult?”". The problem is understanding development the whole way in the detail (whether in biology or cosmology). And it must be understanding IN THE DETAIL because everything else is just hand waving.

So the discussion today is population III stars or NOT; and if so what kind, which properties; and if NOT then how do we explain without them. Not knowing is not an embarrassment or problem; it is a prerequisite for science.

So do you want to know or do you think you already know?

"Population III stars are an important predicition. i.e. first generation stars."

They are the first generation stars (by definition), but discovering them is only to find the earliest stars. It's not a particular discovery proving anything.

Discovering The New World by the Old World was a discovery but wasn't solving any prediction.

Learnt stuff from it? Yup. But it didn't even prove the earth was round or its size.

"(Population III stars) are the first generation stars (by definition)"

NO! Population III stars are hypothesized. "Population III, or metal-free stars is a hypothetical extinct population of extremely massive and hot stars with virtually no surface metals, except for a small quantity of metals formed in the Big Bang, such as lithium-7." Notice the word "hypothetical".

Just as we have the "hypothetical" graviton. But until we have a theory of quantum gravity or some very keen observation; we have no idea if a\the hypothetical graviton is
- a new elementary particle not in the standard model or
- a composite particle of the standard model (i.e. emergent)

Similarly, population III stars are hypothesized.

"despite... the spectacular experimental success of the standard model, the major thrust of particle physics research is aimed at moving beyond it. For all its successes, the standard model says nothing at all about the fourth force: gravity... string
theory postulates that our universe actually contains at least six additional spatial dimensions, each at right angles to the others and yet somehow hidden from view... An interesting question is whether or not eternal inflation makes the big bang nnecessary:
Might eternal inflation have been truly “eternal,” existing more or less the same way for all time, or is it only “eternal” to the future once it gets started? Borde and Vilenkin have analyzed this question (most recently, with Guth), and have concluded that eternal inflation could not have been past-eternal: Using kinematic arguments, they showed [23] that the inflating region must have had a past boundary, before which some alternative description must have applied. One possibility would be the creation of the universe by some kind of quantum process." Alan Guth 2005, arXiv:astro-ph/0502328

Of course the question of past eternal inflation is not settled. e.g.Is Eternal Inflation Past-Eternal? And What if It Is? by Leonard Susskind, Mar 2012, arXiv:1205.0589

Now it would seem to me that if Population III stars are not found that that would be evidence for Past eternal, eternal inflation. But regardless of my argument here.

Arguing that "(Population III stars) are the first generation stars (by definition)" is kind of like arguing that Adam and Eve (by definition) are the first man and woman.

Well cosmology and biology are much too complex sciences to pay attention to such simplistic arguments.

Science is (by definition) only in matters of arbitrary convention (e.g. the length of the king's foot).

"NO! Population III stars are hypothesized"


Your description there is about a hypothesised Population III star. NOT about the hypothesis of the existence of them.

Population III stars will be created out of unsynthesised material.

That is NOT a hypothesis. It is a FACT.

What that sort of star would look like is hypothetical since we don't definitely know what sort we'd be able to see.

Very small stars are most likely able to be Pop3 but we'd be very unlikely to see them because they are small and dim.

So we need to look for the huge stars that are bright enough for us to see at great distances that require them to be still visible for so long after their explosive death (producing pop2 star material).

Pop3 stars are not a hypothesis any more than a proto-hominid between the ape and humans is a hypothesis.

That they would be smaller, stockier, less upright is what we may expect to see such a "missing link" to look like, but the small, stocky and stooped is the hypothetical, NOT the existence of a progenitor.

"A scientific hypothesis is a proposed explanation of a phenomenon which still have to be rigorously tested."

"In the most basic sense, a scientific fact is an objective and verifiable observation."

"Population III, or metal-free stars is a hypothetical extinct population of extremely massive and hot stars with virtually no surface metals, except for a small quantity of metals formed in the Big Bang, such as lithium-7."

"The only problem is that Pop III stars are entirely hypothetical at present. Despite intense searches, no Pop III star has ever been observed. A number of explanations have been put forward to explain this."

There seems to be a missing link in your logic.
But feel free to clarify what proto-hominids have to do with population III stars.

Repeating the same crap again and again isn't proving anything other than you don't understand a bloody word.

Population 3 stars are from the raw matter unsynthesised by earlier populations of stars.


Having atoms heavier than Helium doesn't make them second generation stars produced by earler evolution of stars.


So what exactly is the name of the population III star that you think has been observed? Link please.

Population III stars are hypothetical objects,
just as glueballs are hypothetical objects,
just as preons are hypothetical particlas from which quarks and leptons are composed.
Evidence for all of these hypothetical objects is actively being sought.

Here is wikipedias list of 14 types of hypothetical stars

Please update wikipedia if they have incorrectly placed Population III stars in their list of hypothetical stars!!

Surprised to read that the first stars appeared only 50 million years ago :)

"our best estimates are that if the Universe is 13.73 billion years old now, the first stars formed when it was maybe 13.68 billion years old"

By tom campbell-r… (not verified) on 03 Jan 2013 #permalink

"Population III stars are hypothetical objects,"

No, population III stars (stars that are not the result of condensing star matter) are an inevitable consequence of a universe that started at some point in the past.

They are no more hypothetical objects than my great great great grandmother is.

Though I have no information on her, she still must have existed because I'm here.

The problem is this: Is whatever came before a population II star a star. Or have population II and population I stars (as they are now observed in our visible universe) been the only kind of actual physical starts for the entire 13.7 billion years of the known universe.

As for your great great great..... grandmother. We are very confident that if we go back more than 100,000 or 250,000 years that your great grandmother was not human. We are also very confident that if we go back 85,000,000 years; that your great grandmother would not even be a primate.

Now primates are hypothetical mammals. Many have been observed (both living and in the fossil record).
So no problem, your hypothetical great, great, great.... grandmopther was human, hominid or primate (assuming no mad scientist put you together from the DNA of a female pig and a male human or some other such genetic experiment).

But Population III stars are hypothetical stars.
Just as "Fuzzballs" are hypothetical stars. follow wikipedia link above.

You see Wow, you are seriously confused between
- what is a scientific theory
- what is a scientific hypothesis
- what is a scientific fact

So please provide any link that points to an observed Population III star.

"Population III stars (stars that are not the result of condensing star matter) are an inevitable consequence of a universe that started at some point in the past." But then, if none can be found; then the whole idea that our "universe started at some point in the past" might be at risk.

So let us hope that we do find a t least 1 population III star; or eles, like the search for the Michelson-Morley aether, we may havew to redefine our whole understanding of our visible universe.

The universe never has to be the way that our excellent toy models say that it should. The expectation of science is that our models, laws and theories will have to be modified, will be found to have limits to their domains of relevance, will be superceded by new models, laws and theories. And that the whole truth, no theory of EVERYTHING, will ever be known.

If you WOW can point me to a credible link that says, population III stars have been found; then I will agree that they are not hypothetical.

Population III stars may not be necessary if eternal inflation eliminates the need for a big bang as Susskind, and Guth and others have discussed. Finding an actual population III star that meets the theoretical description (not your hand waving hysterical description) would settle the matter very nicely.

Thus I for one look forward to the experimental finding or not of population III stars in the next decade or few.

I do not want to be like the psuedo evolutionist who proclaims that there must have been an original Adam and Eve; only to find out that DNA analysis show that the orginal human Y (i.e. original Adam) can be dated several millions of years ago; while the original human X (i.e. original Eve) can be dated several hundred thousands of years ago.

Oops, X - original Eve chromosome; never met Y- original Adam chromosome.

Simnilarly, we know nothing about population III stars until we find one.

"Is whatever came before a population II star a star"

If it is burning by fusion of its elements, then it is a star. Whether it comes before a population 2 or after is irrelevant.

"Formation of Population III stars... The question then arises of what happens to these clouds. In some circumstances, one expects them to be disrupted by collisions with other clouds because their cooling time is too long for them to collapse before coalescing. However, there is usually some subgalactic mass range in which the clouds survive. In this case, they could face various possible fates.
- They might just fragment into ordinary stars and form objects like globular clusters.
- On the other hand, the conditions of star formation could have been very different at early times and several alternatives have been suggested.
- The first stars could have been smaller than at present because of the enhanced formation of molecular hydrogen at early epochs.
- They could have been larger than at present because the lack of metals or the effects of the microwave background would increase the fragment mass.
- There may have been a mixture of small and large stars; for example, angular momentum effects could lead to a disk of small stars around a central very massive star, or massive stars could form in the core of the cloud and low-mass stars in the outer regions.
- The first clouds may not fragment at all, but might collapse directly to supermassive black holes or remain in purely gaseous form and become Lyman-clouds.
-This indicates that, although there is clearly considerable uncertainty as to the fate of the first clouds, they could well fragment into stars that are very different from the ones forming today. They certainly need to be very different if they are to produce much dark matter.
- The appellation Population III is sometimes assigned to the first clouds rather than the first stars. However, in this case, all the stars which they spawn must also be called Population III, and this can lead to semantic confusion if the clouds fragment bimodally. It is therefore more sensible to reserve the term Population III for the stars...
- We have seen that one must distinguish between metal producing and dark-matter-producing Population III stars.
-The first must exist, but only warrant a special name if there is a lower cutoff in the metallicity distribution of Population II stars, and IT IS NOT CLEAR THAT THIS IS THE CASE.
-The second may not exist, but, if they do, they certainly warrant a separate name. They would have to be either jupiters or black holes. The detection of microwave distortions would favor the black holes option, but the claim that cooling flows make low-mass stars may favor the jupiter option.
- In principle, both kinds of Population III stars could derive from a single mass spectrum, but that would require the IMF to be finely tuned." Bernard J. Carr, Professor of mathematics and astronomy at Queen Mary, University of London

Which of the above hypothetical population III stars is an observed physical object?
A) all of the above
B) none of the above
C) we don't know yet
D) it is impossible to ever know
E) one of the above must be correct; but it is impossible to know which one
F) only Wow hairdresser knows; but he is sworn to secrecy

Your question:

"Which of the above hypothetical population III stars is an observed physical object?"

indicates that you know what I mean but have absolutely no clue what it means to say that.

Population III stars are not hypothetical if you're deciding that Pop3 stars are made from pristine matter.

Those Pop3 stars are no more hypothetical than my great great great grandmother is a hypothesis.

My grandmother may be

a) from Ireland
b) from Scotland
c) from Eastern Europe

THOSE are hypothetical great great great grandmothers. Moreover, these are not *necessarily* the truth and what the truth is won't be known until after I see some evidence of her existence.

But despite not having ANY evidence of her existence, SHE MUST STILL EXIST.

If you think my great great great grandmother is ONLY hypothetical, please let me know where I came from.

PS unlike you, I can do independent thought and don't have to ask my hairdresser.

I am assuming here your assinine comment about hairdressers is merely projection since otherwise that little piece of excrement you shat out your mouth there is merely the diseased ravings of a lunatic with their brain in freefall.

And could you please at least acknowledge when you're abandoning a previous assertion?

You started off using "this star has some heavier elements in it therefore it can't be population 3".

You have now apparently given that up.

Can you confirm or deny.

First, I leave the determination of whether Caffau's star is a population III star or not to professional astronomer's.

I was quoting Elizabeth Caffau (the astronomer for whom Caffau's star was named. She said, "“But to explain the presence of a small amount of metals, it has been formed from material contaminated by the ejection of at least one massive star. Therefore it is at least a second generation star.”

Here is the real issue Wow as I see it.

You have used many anaalogies from biology "missing link", your "great great... grandmother." etc.

So let us use a really analogous biological analogy.

There are two types of cellular organisms on planet earth
- prokaryotic (i.e. bacteria)
- eukaryotic (i.e. animals, plants, fungi, protocista)

These are the only two observed cell types. Both occur in the fossil record and both are currently alive and thriving on earth today.

But abiogenesis (the formation of living cells from inert matter) has a problem. Biologists can't figure out how to get from non-living matter to the complexity of living matter.

They do know that living cells first appear in the fossil record perhaps 3.9 billion years ago. But biologist are not sure if which hypothetical protocells or some other biological explanation is needed to get from the observed to what seems necessary.

At any rate protocells of some sort are just one hypothetical explanation for abiogenesis.

Now back to stars.
Population I stars are the most advanced (like eukaryotic cells)
Population II stars are less advanced (arrived earlier in cosmic history than population I stars; just as prokaryotic cells preceded eukaryotic cells evolutionarily).

And finally Population III stars are hypothetical protostars (analogous to protocells )

Now neither Population III stars nor protocells have been observed. And something like Population III stars seems necessary for star evolution theory; in a way similar to something like protocells seems necessary for cellular evolution theory.

But biologist have the good sense to be open to many hypotheitical explanations and have not declared protocells a fact; as you Wow (supposedly an astronomer) have claimed population III stars a fact.

In my mind, good science requires that we honestly say we don't understand how we got from A to C though we thing we understand how to get to D.
- in star evolution, A is gas clouds
-------------------------B is perhaps hypothetical population III stars
-------------------------C is population II stars
-------------------------D is population I stars

in cellular evolution, A is primordial soup of chemicals including RNA
----------------------------B is hyopotheticaal protocells or some other explanation
----------------------------C is prokaryiotic cells
----------------------------D is eukaryotic cells

In my mind science becomes a psuedoscience when it prematurely declares certain things logically necessary. e.g. obviously there is no upper speed limit, obviously the universe has only 3 spatial dimensions, obviously there must be protocells, obviously their must be protostars (i.e. population III stars).

The science minded need to be strong enough to weigh the evidence and wait for sufficient evidence; and not prematurely believe in any major or minor god. e.g. the god of determinism or the god of protocells, or the god of population II stars, of the God who fixes all these things that science should just honestly admit that, "We do not know yet."

So Wow, glad you know. Please provide a link to observed population III stars.

I'll leave you the last comment. Ciao.

Your attempt there to classify abiogenesis is still obscured by the number of words you're putting into it and the irrelevant obsession you're continuing with it.

There MUST HAVE BEEN stars that were not formed from other star's dying expulsion of material if the universe started a finite time ago.

The existence of population 3 is NOT a hypothesis.

It's no more a hypothesis than "life must have started on earth at some point".