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"Generations" of star formation

small axe

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A few basic questions I hope someone can help me with!

Watching a HISTORY CHANNEL show last night, the narrator was speaking about how "we are made of stardust" etc ... How every element that makes up planets and people were formed in stars via fusion into heavier and more complicated atoms.

Firstly, he mis-spoke, right?
Hydrogen wasn't formed in stars, hydrogen is the simplest atom that resulted from (or at least already existed after) the Big Bang ... Hydrogen needn't be created in stars then ejected into the Universe, it just formed when the Universe cooled down enough to become "matter"

I think I'm right there?

----> But my main question is: How many "generations" of stars (the first star forming, fusing heavy atoms, exploding or dying ... the second "generation" of stars forming out of the first stars' debris and cooking up more atoms ... dying and ejecting its debris ... etc) are needed before the Universe has all the necessary complex atoms to make planets and people?

If the universe is 14 billion years old, and our Sun or earth is already 4 billion years old (but has a life expectancy of 10+ billion years) ...

How many generations of stars have lived and died to make us? It can't be many.

And since the debris cannot be "traveling" very fast, if it's slow enough to be captured by mere gravity into lumps to become new suns and planets ...

----> How far away can the debris have traveled from? Not horribly far, on a cosmic scale? (For instance, can we contain atoms formed in another galaxy's stars? or are they too far away?)

And, to ask the dumbest of questions: I hear often that to look at a star 5 billion light years away means we're seeing it as it was 5 billion years ago (when its light left it) ... So that same star has been evolving and changing for 5 billion years, what we see as "the early structures of the universe" are long ago gone?

----> Are there then possible structures and forms of our existing universe we can by definition know nothing about? If there's dark matter and energy, and it's 5 billion years away, can it be undergoing weird changes that dark matter and energy isn't undergoing anywhere nearby where we can ever hope to study it?

Could there be some other, different sort of space-time at work far away, that suddenly reaches us and changes everything?

I don't mean in the "It's Sci-Fi, write any crap you imagine" way, but in a valid "Here's where our Scientific knowledge just cannot be known to hold true" way?

Anyway ... any answers or insights will be a help, and I apologize if I'm asking stoopidity! :cry:
 

efkelley

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Because I actually MUST get some writing done today, I'm going to keep my answers short. Lhun and GregFOTS will fill in the blanks, I'm sure.

Watching a HISTORY CHANNEL show last night, the narrator was speaking about how "we are made of stardust" etc ... How every element that makes up planets and people were formed in stars via fusion into heavier and more complicated atoms.

Firstly, he mis-spoke, right?
Hydrogen wasn't formed in stars, hydrogen is the simplest atom that resulted from (or at least already existed after) the Big Bang ... Hydrogen needn't be created in stars then ejected into the Universe, it just formed when the Universe cooled down enough to become "matter"

I think I'm right there?

Yes, hydrogen is the most basic element. It didn't form from stars, it forms stars. However, everything from helium on up was formed within the crucible of a star's center.

How many generations of stars have lived and died to make us? It can't be many.

Some stars can have very short lifespans. Possibly less than a billion years. My admittedly hasty scan of the intertron did not find a minimum. So, in theory, there could have been as many as 14 generations between the beginning and us.

It's probably safe to say that the generations in our little pocket of the universe are probably between two and five.

And since the debris cannot be "traveling" very fast, if it's slow enough to be captured by mere gravity into lumps to become new suns and planets ...

When a star explodes, the ejecta can be traveling at nearly lightspeed. It's own gravity will eventually slow it down. This is where nebulae come from. Eventually all that stuff will swirl back together and form a new star (and often multiple stars).

And, to ask the dumbest of questions: I hear often that to look at a star 5 billion light years away means we're seeing it as it was 5 billion years ago (when its light left it) ... So that same star has been evolving and changing for 5 billion years, what we see as "the early structures of the universe" are long ago gone?

Yep!

Are there then possible structures and forms of our existing universe we can by definition know nothing about?

Possibly! Fun innit?

If there's dark matter and energy, and it's 5 billion years away, can it be undergoing weird changes that dark matter and energy isn't undergoing anywhere nearby where we can ever hope to study it?

For some really fun stuff, consider that the universe is accelerating its expansion. Eventually, we won't be able to see anything beyond our galaxy because it will be moving away too fast for coherent light to reach us. Fun eh?

Could there be some other, different sort of space-time at work far away, that suddenly reaches us and changes everything?
I don't mean in the "It's Sci-Fi, write any crap you imagine" way, but in a valid "Here's where our Scientific knowledge just cannot be known to hold true" way?

What you're talking about there would be a fundamental change in the way that matter or energy interacts with the universe. It's safe to say that we don't know enough about the universe to determine whether or not this is possible. But what you're describing is akin to The Big Rip

Have fun with the See Also section of that article! :D
 

Sarpedon

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The larger a star is, the shorter its life will be. The most massive of the 'supergiants' last only a few hundred thousand years, and many astrophysicists think that the first few generations of stars were mostly of this type.

Also, only the largest stars form elements heavier than iron. Iron is at the tipping point in nuclear energy. When you combine elements lighter than iron in nuclear fusion, more energy is released than is required to start the reaction. When you combine elements heavier than iron, it consumes energy. Likewise, when heavy elements (like Uranium) decay into lighter elements, it releases energy. Heavy elements are only formed in the death throes of giant stars. Iron is kind of like cancer to a star: when it starts forming, the end is near. Because it releases no more energy than it absorbs, the star can't maintain the precarious balance between gravity crushing it down and the energy released by fusion pushing back out.
 

small axe

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Well, it's been very helpful and mind-opening already! So even fast-burning stars can make the heavy atoms? I guess I had assumed (wrongly) it took billions of years of cooking for a star to progress through the elements-building stages. So the fast short-lived ones just do it all, but faster?

And the thing about IRON being a death-knell to stars, that's like spooky poetry. Vampiric and doomed, takes more energy than it gives!

Again, thanks! Very evocative answers! Any added insights by others are invited!
 

efkelley

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Well, it's been very helpful and mind-opening already! So even fast-burning stars can make the heavy atoms? I guess I had assumed (wrongly) it took billions of years of cooking for a star to progress through the elements-building stages. So the fast short-lived ones just do it all, but faster?

And better. They've got higher heat, higher pressure, and more mass to create heavy elements with. They're also more likely to go FOOM! so all those heavy elements get released into the interstellar medium.

Sorry about the name, Greg. I posted before having my morning rum.
 

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Well, it's been very helpful and mind-opening already! So even fast-burning stars can make the heavy atoms? I guess I had assumed (wrongly) it took billions of years of cooking for a star to progress through the elements-building stages. So the fast short-lived ones just do it all, but faster?

And the thing about IRON being a death-knell to stars, that's like spooky poetry. Vampiric and doomed, takes more energy than it gives!

Again, thanks! Very evocative answers! Any added insights by others are invited!

Some clarification, if it is necessary: Stars can build atoms through the normal fusion process only up to iron (element 26)*. Iron simply does not fuse. When all the fusable atoms are used up, and the stable iron core is essentially all that remains, the star implodes, and the colossal energy generated by that implosion is what creates all the heavier atomic nuclei.

*A possible exception is fluorine (element 9), which is, as I understand it, the least abundant of the first 26 elements in the periodic table. Its generation by means of standard fusion is something of a mystery, and it may also only be generated in supernova blasts.

Also, just for clarification, astronomers consider every element heavier than helium to be a "metal". So when they speak about "metals" in stars, they are talking everything from lithium (element 3) on up, including things like carbon, nitrogen, oxygen, neon, argon, sulfur, etc.

caw
 

Misa Buckley

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God, I love science.

I should have told my parents where to get off and studied astrology after all. Love this stuff. It's just so fascinating.
 

Sophia

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God, I love science.

I should have told my parents where to get off and studied astrology after all.

LOL! I'm going to assume you did that deliberately - well done. :D

small axe: A couple of specific things that you could look up to get more information are primordial nucleosynthesis, for information on how hydrogen, helium, deuterium, tritium and lithium first formed, and as an example of early structure in the universe that we can still observe, the last scattering surface. This will be described in articles about the cosmic microwave background radiation.

Stellar evolution is another category to look into. All stars (except for the tiniest ones) go through a period on the main sequence where they burn hydrogen to helium in their core. The more massive a star, the faster this happens. (More mass means a higher temperature, and the rates of the hydrogen-burning nuclear reactions vary with temperature. "Live fast, die young" is the rule with stars.) Their mass when they enter the main sequence phase determines what happens to them afterwards, when the hydrogen in their cores is used up. Look at what happens to the stars in the post-main sequence stages of their evolution to see how they enrich the interstellar medium with the higher mass elements.
 

small axe

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Originally Posted by misaditas
God, I love science.

I should have told my parents where to get off and studied astrology after all.

LOL! I'm going to assume you did that deliberately - well done. :D

No need to "assume" ... the position of Mars in the constellation Aquarius dictated that it would be done! :)

Thanks for the added info!
 

efkelley

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Some clarification, if it is necessary: Stars can build atoms through the normal fusion process only up to iron (element 26)*. Iron simply does not fuse. When all the fusable atoms are used up, and the stable iron core is essentially all that remains, the star implodes, and the colossal energy generated by that implosion is what creates all the heavier atomic nuclei.

If wikipedia is to be believed, (http://en.wikipedia.org/wiki/Iron#Isotopes) Iron does, in fact, fuse, and it does fuse within active stars. But! Iron and nickel are two of the most stable elements extant. Fusing them is very very difficult, and extremely inefficient.
 

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If wikipedia is to be believed, (http://en.wikipedia.org/wiki/Iron#Isotopes) Iron does, in fact, fuse, and it does fuse within active stars. But! Iron and nickel are two of the most stable elements extant. Fusing them is very very difficult, and extremely inefficient.

You are correct, technically; I simplified my statement a little more than perhaps I should have. What I meant was that iron cannot produce energy via fusion. To force iron nuclei to fuse, you have to put more energy in than you get out. A lot more energy, in fact. Phrased another way, in a succinct answer I found on-line:

to fuse iron into heavier elements requires more energy than is released by the fusion reaction, thus making the reaction unsustainable.

So the iron core of an exhausted star collapses, and the energy of that collapse is what will fuse iron nuclei into those of heavier elements.

caw
 

small axe

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Anyone have an estimate of "What's the oldest star that could have an intelligent, technologically-advanced civilization orbiting it?" then?

If the oldest stars would be by these criteria (if I'm hearing you all right?) fast-burners that burn out young, and not orbitted by planets with heavier elements (say, rocks and irons etc) because no stars before them had time to fuse it and spit it out ...

And the Universe is only around 14 billion years old ...

Can there be a 10 billion year old "Earth-like" planet?

Any ideas / guesses on what "generation" our sun might be, that an ancient Alien might comment about how many generations of stars died before ours could be born? That would be a pithy comment.

Would it be safe (without inviting calls of 'bad science" writing) to have a character say: "More stars have lived and died than have existed since earth's Sun was born?"

If young stars burnt faster and died, were there logically more of them ... in the sense that every one, later star is now made up from the debris of several previous stars?

I know we don't know ... I'm just wondering about "safe guesses or speculations" etc!

Thanks!
 

blacbird

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If young stars burnt faster and died, were there logically more of them ... in the sense that every one, later star is now made up from the debris of several previous stars?

It's not an issue of "young" stars burning faster. It's an issue of BIG stars burning faster. Size is the main criterion for how long a star will live. The bigger, the faster they go. Stars bigger than the Chandrasekhar Limit (1.44 solar masses) are the ones that catastrophically blow up in supernovas, because they are simply too big to resist total gravitational collapse when that iron core is developed. The biggest ones may last no longer than about 1 million years, as opposed to the 10 billion years or so that a sun-sized star can expect to hang around. Smaller red dwarf stars will live much longer even than that. In fact, the universe is still so young (13.7 billion years is the current best estimate) that no red dwarf stars have lived through their entire life-cycles yet.

caw
 

FOTSGreg

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Anyone have an estimate of "What's the oldest star that could have an intelligent, technologically-advanced civilization orbiting it?" then?

Probably almost impossible.

If we use our own homeworld as an example, it took almost 1.5 billion years for Earth to cool down enough and to accumulate enough atmosphere to allow sustainable life - and that life was not oxygen-breathing. Life on Earth has been around for around 3.5-4 billion years of its existence, but for almost all of that time period, up through and including most of the last 0.5 billion years, life has been simple single-celled organisms. It's only in the last half billion years or so that multicellular life has evolved and only within the last 3-5 million years that anything resembling sentience has evolved in a single isolated species on a single isolated planet in a single isolated system about 2/3rds of the way out in the galactic wilderness from the galactic core.

It takes a long time for life to develop and any number of absolute statistical miracles for sentience to develop.

I would expect there are planets teeming with life scattered throughout the universe, but it's mostly single-celled life.

There just hasn't been enough time for multiple sentient species to develop yet.

In fact, we might be the first.
 

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There just hasn't been enough time for multiple sentient species to develop yet.

In fact, we might be the first.

Highly doubtful. The solar system is less than 5 BY old. There are many many many stars in our galaxy alone that are older than that. Time is not really an issue.

That being said, I greatly doubt we will ever make contact or detect the existence of sentient life forms elsewhere, owing principally to the colossal distances likely to be involved. But the discovery of even the most primitive microbiology (even extinct fossil stuff) elsewhere would be an immense advancement in our understanding of how things work. And, if anything, this possibility looks more likely now than ever, with the discoveries on places like Europa and Enceladus.

caw
 

FOTSGreg

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blacbird, I disagree - time is an issue. From our own history we know it takes a tremendous amount of time and an extraordinary series of conditions and a few outright miracles for life to develop and an even more extraordinary series of events and miracles for sentience to evolve from that life.

Okay, say the universe is 15 BY old. We know, from our history, it takes roughly 3.5 BY for life to develop on a world and another 0.5 BY for sentience to raise its ugly head and look at the stars above. So, let's call it 4 BY for sentience to evolve.

Now, I figure we can rule out the first 5 BY after the Big Bang simply due to the fact that heavy elements hadn't really had a chance to become widespread through the universe by then. So, that leaves us with 10 BY. 10/4=2.5 possible sentient evolutions. Now, this occurred on a planet around a yellow dwarf out in the last third of the galactic spiral.

We can probably eliminate the stars in the center 1/3rd of the galaxy as possible candidates for life as that region is too active for sentience to have received the 4 BY it needs to evolve before something catastrophic wipes life off the world it resides on.

So, instead of a hundred billion stars, we're left with around 2/3rds of that. Most of the stars in the outer galactic rim are old and heavy metal poor ( think, I could be wrong here). So, let's assume that another 1/3rd of the galaxy's stars are unsuitable for life. That leaves us with around 30-35 billion candidates. You can throw out at least 90% of these right off for various reason - too much luminosity, not old enough, too old, flare stars, Wolf-Rayet stars, binary stars, red giants, blue dwarves, etc., etc., etc.

That leaves us with 3-4 billion stellar candidates that need to have had at least 4 BY of essentially undisturbed planetary evolution for the planets within their terrestrial zones to have evolved sentient life.

I'd bet life is everywhere out there, but sentient life is a tiny, tiny percentage of that life.
 

blacbird

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Okay, say the universe is 15 BY old. We know, from our history, it takes roughly 3.5 BY for life to develop on a world and another 0.5 BY for sentience to raise its ugly head and look at the stars above. So, let's call it 4 BY for sentience to evolve.

I agree with your timing on the emergence of sentient organisms on the planet. But the first living things on Earth date back to something like 3.8 BY, certainly less than 1BY from the formation of the planet. Some scientists are suggesting even earlier.

And we have exactly one data set to work from. Extrapolating that as the universal norm is hardly valid. We have only recently discovered that our solar system isn't even close to the standard model for other stars.

We know, from our history, what it took for things to work on our planet. And that's about as far as we can sensibly extrapolate.

And even then, we know of Sun-like stars much older than our own. We see the death throes of these things as planetary nebulae. Those probably are in the realm of 8-10 billion years old, given our extrapolation about the length of Sol's life. And there are lots of sun-like stars in between 4.5 and 8 billion years old.

caw
 

kuwisdelu

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Oh lordy.

To put it simply: the universe is a f*cking big place.

Plenty big enough for there to exist other stars with other planets where sentient life has likely developed. But as blackie said, it's perfectly likely, due to the distance, that we won't even know for sure.
 

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Seems there is some difficulty deciding on whether we're discussing life in the universe or life in the considerably more restrictive yet still vast local galaxy.
 

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I've heard it said that human civilization is now much more difficult to detect now than it was 40 years ago.

Nowadays, most of our radio communication is relatively low power, and directed from satellites towards the earth, rather than huge antennaes blasting thousands of megawatts in all directions.
 

Albedo

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I've heard it said that human civilization is now much more difficult to detect now than it was 40 years ago.

Nowadays, most of our radio communication is relatively low power, and directed from satellites towards the earth, rather than huge antennaes blasting thousands of megawatts in all directions.

Another good answer to the Fermi paradox. Industrial civilisations remain electromagnetically noisy for ~80 years, then turn inwards and then collapse from environmental destruction, oil depletion and/or nuclear war becoming insular xenophobes hermits.
 

FOTSGreg

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There's also a difficulty with discussing sentient life versus just plain life as simple as virii or bacteria.

Ethically, I think that discovering virii or bacteria is going to be much less controversial than discovering a sentient life form that might eventually have the capacity to challenge what we perceive as our "rightful place" in the universe.

It is not entirely true that only sentient life has the ability to challenge our existence as a species. Virii and bacteria have done far more harm to the human race than we have to each other.

I'll concede blacbird's argument that "life" has existed on this planet for about 3.8 BY, but I maintain that sentient life has only existed for about the last 3-5 million, a tiny fraction of that 3.8 BY span, and that the evolutionary pathways and challenges that allow sentience to develop (or force it to) are extraordinarily rare such as to make their actual occurrence a near-miracle.

Yes, there are billions of galaxies in the known universe with trillions of stars contained in them. Somewhere out there I think there must be other sentient life. I also think the universe flourishes with life at some level.

Our galaxy, however? I think the odds are extremely good that we are alone (or at least the first) on the sentient level.