Massive blue giant stars after the first 700 million years.

[dougettinger]

As the known universe began to expand and fermions were created after the first 700 million years after the Big Bang - what is the predicted average spacing of the first stars and their predicted average size? In addition, does any hypothesis exist to predict the number of cycles for the repetition of supernova explosions and subsequent reforming of the next generation of stars?

[Wayne]

No idea on the average spacing, but population III stars were quite odd to anyone who has a vague understanding of the various fusion processes.

A "normal" O or B class hydrogen fusing star uses the CNO cycle, a process involving catalysis by carbon, nitrogen and oxygen. However, these elements weren't present for the first population of stars, which instead had to use the proton-proton chain.

This meant that the cores of population III stars were much hotter than their population I analogues formed today (or in the last ten billion years or so) because the proton-proton chain is much slower than the CNO cycle, hence if the CNO cycle can produce the necessary energy, it will and prevent the core from heating enough to accelerate the proton-proton chain.

If the core was very hot, we know that the star would expand its outer layers. This means that early stars would not be blue at all, but would all be red.

We know extremely little about population III stars and it's perfectly possible they didn't form at all. The initial hydrogen collapse could grow out of control without stable fusion ever being reached and then explode as a pair-instability supernova without ever steadily burning hydrogen.

[dougettinger]

Wayne, are you saying that there is no hypothesis for the nucleosyntheisis of Population III stars? Where eventually do the the heavier metals of carbon, nitrogen and oxygen come from? Do the rapid-fire explosions create these materials?

The Big Bang theory does predict the timeline for the creation of the first stars. I presume that all the regular matter in the universe at this time existed at the beginning of star-making. What percentage of that matter went into the first stars as predicted by the theory? I am trying to estimate a very rough density for stars in the beginning such as 0.01 light years if this is possible. Does any hypothesis predict their average size? Some of the largest stars discovered today are 100 and possible 200 solar masses. At what star size does nucleosynthesis fail to work?

[Wayne]

I'm saying nothing of the kind, only that we know extremely little about how Pop III stars behaved.

Nucleosynthesis was done by these stars, whether they actually could support themselves for any amount of time or whether they could not. The end result would be a supernova and it's well known how supernovae can create metals.

[dougettinger]

No idea on the average spacing, but population III stars were quite odd to anyone who has a vague understanding of the various fusion processes.

A "normal" O or B class hydrogen fusing star uses the CNO cycle, a process involving catalysis by carbon, nitrogen and oxygen. However, these elements weren't present for the first population of stars, which instead had to use the proton-proton chain.

This meant that the cores of population III stars were much hotter than their population I analogues formed today (or in the last ten billion years or so) because the proton-proton chain is much slower than the CNO cycle, hence if the CNO cycle can produce the necessary energy, it will and prevent the core from heating enough to accelerate the proton-proton chain.

If the core was very hot, we know that the star would expand its outer layers. This means that early stars would not be blue at all, but would all be red.

We know extremely little about population III stars and it's perfectly possible they didn't form at all. The initial hydrogen collapse could grow out of control without stable fusion ever being reached and then explode as a pair-instability supernova without ever steadily burning hydrogen.

In the previous reply, the first stars after the universe's age of 700 million years, could have possibly been supermassive stars creating pair-instability supernovae and hypernovae. Can I safely assume as the universe continued to expand, smaller size second and third generation stars would have been created that were in the range of 80 to 130 solar masses? Do you imagine at any one point in this early cycle of star birth and death, that the ensuing supernovae created a domino effect starting explosions in thousands or millions of stars in a brief time span? I am trying to comprehend a very dense universe in early times and what was occurring.

[Wayne]

That's by no means out of the question. The early universe was a pretty dense and very energetic place but we think that part of the initial formation of galaxies was around black holes (the "black hole came first" hypothesis).

While a supernova does cause giant molecular clouds to collapse in places (we believe that the formation of the Sun was triggered by a supernova or that at least the early solar system was very close to a supernova), they also sculpt out large voids. So such a "domino effect" would be present, but not really to the kind of spectacular level that every galaxy would have a supernova going on at the same time.

Once metals grew to enough of a level that the CNO cycle was able to provide substantial amounts of energy (population II) then the entire population III fireworks display plain stopped. This means that your 700 million years is a bit out: Population II was well underway as the globular clusters formed just 600 million years into the universe. The pop III stars (live fast, die young, no pop III star lasted more than half a million years and this is one of the problems we have in physics right now) were a feature of the 400 million year old universe, though they may have lingered in low mass irregular galaxies until much later.

[dougettinger]

That's by no means out of the question. The early universe was a pretty dense and very energetic place but we think that part of the initial formation of galaxies was around black holes (the "black hole came first" hypothesis).

While a supernova does cause giant molecular clouds to collapse in places (we believe that the formation of the Sun was triggered by a supernova or that at least the early solar system was very close to a supernova), they also sculpt out large voids. So such a "domino effect" would be present, but not really to the kind of spectacular level that every galaxy would have a supernova going on at the same time.

The domino effect that I refer to is not between galaxies but between neighboring stars in the same star field in the very compressed early universe. Perhaps scientists cannot possibly guess about this domino effect.

Once metals grew to enough of a level that the CNO cycle was able to provide substantial amounts of energy (population II) then the entire population III fireworks display plain stopped. This means that your 700 million years is a bit out: Population II was well underway as the globular clusters formed just 600 million years into the universe. The pop III stars (live fast, die young, no pop III star lasted more than half a million years and this is one of the problems we have in physics right now) were a feature of the 400 million year old universe, though they may have lingered in low mass irregular galaxies until much later.

I am not familiar with the "black hole came first" hypothesis. But I do believe the capturing or combining of numerous black holes created the seeds for galaxy formation. But the initial black holes had to come from Pop III stars. Am I correct in assuming this for the currently accepted hypothesis?

Please excuse my timeline errors. I am not totally current. My main issue or problem is what happened between 13 bya and 4.5 bya before our solar system was born. How did we arrive at our neighboring star field parameters of high metal stars, the average size of one solar mass, and spaced 4 ly's apart? Did star birth and death cycles occur 10x, 100x , or ?x during that time span? What do the astrophysicists say about this topic if anything? I am trying to stay independent of galaxy formation, but this may not be possible.

[Wayne]

There are two schools of thought in galaxy formation (no, you can't escape it!).

The first one I'll discuss is "stars came first" that a cluster of stars used their gravity to draw in more material and so set off galaxy formation. The central black hole simply sank there and absorbed more mass as time went on. It has enough support to not be discountable, but doesn't have a majority of support.

The second is "black hole came first", that galaxies grew around the central black hole.

On to your questions.

Initial black holes need not have come from any stars at all: Primordial black holes (those formed before the surface of last scattering) may have accreted enough mass to become stable and and then become the seeds of galaxies. This is part of the "Black holes came first" idea. Perhaps some did, perhaps some didn't. Due to the destructive nature of black holes their age cannot be measured, only inferred, estimated or plain guessed.

The average size is not one solar mass. The Sun is more massive than 85% of all other stars. Most stats are dim K and M class red dwarfs (and theory predicts that even they are outnumbered by brown dwarfs ten to one).

The average spacing is not 4 lys, it's around 0.1 Msun/pc^3. This works out to a mean distance between stars of around 1.4 ly.

The Sun's neighbourhood is quite anomalous (don't read much into this, it was passing through a very dense region just 30 million years ago - The non-avian dinosaurs are over twice as old) in that it contains many massive stars and few normal stars. Related to this, the average spacing is much higher than normal, within 20 light years the average spacing is around 3 ly (counting binaries as one). The Sun itself is on the high side of spacings, but in just a million years, Gliese 710 will pass by at just over 1 ly.

[dougettinger]

There are two schools of thought in galaxy formation (no, you can't escape it!).

The first one I'll discuss is "stars came first" that a cluster of stars used their gravity to draw in more material and so set off galaxy formation. The central black hole simply sank there and absorbed more mass as time went on. It has enough support to not be discountable, but doesn't have a majority of support.

The second is "black hole came first", that galaxies grew around the central black hole.

On to your questions.

Initial black holes need not have come from any stars at all: Primordial black holes (those formed before the surface of last scattering) may have accreted enough mass to become stable and and then become the seeds of galaxies. This is part of the "Black holes came first" idea. Perhaps some did, perhaps some didn't. Due to the destructive nature of black holes their age cannot be measured, only inferred, estimated or plain guessed.

The average size is not one solar mass. The Sun is more massive than 85% of all other stars. Most stats are dim K and M class red dwarfs (and theory predicts that even they are outnumbered by brown dwarfs ten to one).

The average spacing is not 4 lys, it's around 0.1 Msun/pc^3. This works out to a mean distance between stars of around 1.4 ly.

The Sun's neighbourhood is quite anomalous (don't read much into this, it was passing through a very dense region just 30 million years ago - The non-avian dinosaurs are over twice as old) in that it contains many massive stars and few normal stars. Related to this, the average spacing is much higher than normal, within 20 light years the average spacing is around 3 ly (counting binaries as one). The Sun itself is on the high side of spacings, but in just a million years, Gliese 710 will pass by at just over 1 ly.

Thank you for explaining average star size and spacing. I have never read about these facts. Is this average star spacing based on spiral or elliptical galaxies or both? Also, do globular clusters of stars have an anomalous average spacing different from what is stated?