Friday, January 07, 2011

Star Stuff Contemplating Star Stuff

"We are star stuff contemplating star stuff."
Carl Sagan

Star light, star bright,
Ten billion years ago,
I need to ask a question
Cos I really want to know:

The carbon in our bodies came
From ancient stars’ collapse;
I’ve heard it from a poet
Or a physicist, perhaps

But is it true, as some have said
(I can’t believe it, quite),
That different stars made atoms
For my left hand and my right?

Or could it be, my love and I
Were once the self-same star,
Together for eternity
In time and space, so far?

Something I have wondered for years--probably from about six seconds after I first heard about how heavier elements were formed--is, how was (is) the matter from exploding stars distributed? Space is, as Douglas Adams noted, big. "[V]astly, hugely, mind-bogglingly big." If a star goes supernova, how widely would its heavier elements be distributed? Would the majority of the "star stuff" coalesce into just a relative handful of relatively local gravity sinks, or could we expect a relatively small amount in any one relatively local area (and yes, I thought about each of those relatives; it's my version of Drake's equation).

Lawrence Krauss, in his wonderful "A Universe From Nothing" talk, gives one answer:
Every atom in your body came from a star that exploded. And, the atoms in your left hand probably came from a different star than your right hand. It really is the most poetic thing I know about physics: You are all stardust. You couldn’t be here if stars hadn’t exploded, because the elements - the carbon, nitrogen, oxygen, iron, all the things that matter for evolution and for life - weren’t created at the beginning of time. They were created in the nuclear furnaces of stars, and the only way for them to get into your body is if those stars were kind enough to explode. So, forget Jesus. The stars died so that you could be here today.
On the other hand, Tony Piro's "Calamities of Nature" claims "we're all born from the death of the same star"

(Click to see the whole thing.)
Anyway, I want to know. And here's the beautiful thing. Once upon a time, we would have made up some answer, something that made us feel good, or superior, or something that allowed the teller to pretend to know more than he or she did. Something that probably started "once upon a time". Or "in the beginning...". But now, we can actually answer the question. It doesn't matter which I think is cooler, or more romantic, or more commonsensical. There is a right answer, and if there aren't people who know it right now, there is a methodology that allows us to eventually get there.

Assuming our own star doesn't blow up first.

Anyway, I've got great commenters here, and I'm hoping one of you knows, or knows someone who knows. How many stars died to make me? Are my right and left hands from different stars (seems impossible to me, given that they came from the same food and air I've been taking in over my lifetime, so I suspect Krauss was using a bit of poetic license, actually meaning that our entire bodies are composed from the remains of many stars--but how many?)?

I want to know.


Cyc said...

It is hard to say exactly how many, but we can certainly say it was quite a few. The first stars formed about 100 million years after the big bang. These first stars, being quite massive had life spans in the tens of millions of years. And just like in the stellar nurseries of today, when a star goes supernova, it ends up compressing the surrounding gas allowing for more star formation. At about the one billion year mark there were massive stars coming and going constantly. Their death nulls would scatter their newly fused atoms across the early galaxies, entangling with the debris of countless other stars. Step ahead just over five and a half billion years and we start to see the formation of our solar system. So there was plenty of time for a myriad of stars to give their lives for us to be as we are now. In fact, with the amounts of some of the products and the densities we see now, there had to be quite a few of them. So yes, it is quite likely that the atoms in one hand did originate from an utterly different star then the other. But even more astonishing is that they were distanced not just by space as we often imagine but by enormous amounts of time. So not only are the atoms different in origin, but also different in age.

Quodlibet said...

"There is a right answer, and if there aren't people who know it right now, there is a methodology that allows us to eventually get there."

I love that. It is rational and reassuring (not that we need reassurance about any of this). It's OK not to know all the answers (yet). People who are uncomfortable with the unknown invent religions to "answer" the "questions." I'm OK with the unknown, and with science's beautiful journey of contemplation and discovery.

Cuttlefish said...


Ok, Cyc... to probe, just a bit. First off, although it makes perfect sense now to think of an overlapping historical succession of stars each contributing atoms to what eventually becomes our solar system, our planet, ourselves, our hands, it seems there cannot be any particular reason that the atoms in my two hands are any more different than two atoms side-by-side in the cuticle of my thumbnail. The "Caesar's last breath" thought problem (that's about the depth I go) suggests that the dispersal of these atoms in the lengths of time we are talking about is bound to be quite widespread, at least within localized areas like our biosphere.

Plus, of course, I started as one fertilized egg, so unless there is a plan where all of one star's atoms go one direction and all the other's go another... So, yeah, unless there is something I am missing (and that is always a strong possibility), the arbitrary assignment of separate star-stuff to separate hands would be like taking several billion decks of cards, shuffling them well, and just by chance alone dealing all the reds to one hand and all the blacks to another.

The right/left language is a helpful bit of linguistic license, but the bottom line is that we are made of the stuff of myriad stars (though I love the word "myriad", I am curious as to whether we can narrow it down to a reasonable confidence level).

But now, your very helpful explanation raises another question for me--could both Krauss and Piro be right (or, close enough for gubmint work)? Our most recent ancestor-stars were, themselves, the descendants of earlier stars, which were the descendants of earlier, and so on. Could it be that we are now, say, 90% or more composed of the atoms of one particular most recent ancestor star, while at the same time being the descendant of thousands or millions (or more?) of more distant (in age, as well as space) stars?

And, the last bit... how do we know all this? (or should I just sign up for the course, or buy Krauss's book?)

Cyc said...

There are a few things to consider Cuttlefish. First, you are right, it is impossible to say if the atoms in one hand are certainly different from those in the other, but statistically they are. In fact a great deal of the atoms in any part of your body are from different stars (once again, statistically).

You asked if possibly there were a final star that all our atoms went through. Probably not, as remember, stars form out of primarily hydrogen and helium, the heavier elements tends to accrete around the star. These heavier elements are the residue of so many previous stars. And when this final star died, it would then mix up its parts with both the accretion disk as well as the other gasses in the stellar nursery that eventually formed our sun.

To further complicate things, remember that as the Earth formed, it didn't just form from the bodies within its orbit, it also was hit by another planet (Thera, which gave us our moon and some extra mass) as well as massive bombardment from comets and asteroids that happened to be torn from the outer solar system by all the gravitational havoc (which is probably the reason our planet has so much water and possibly even the large amount of organic molecules). So by now, Earth is quite the hodge podge of materials from different parts of the solar system which in turn are from different stars.

To make matters even more confusing, remember that you probably don't have a single atom that you were born with. Your entire body renews itself entirely every seven years, down to the atom. In fact, the Earth itself, in this way, is a perfect analog to how the star stuff got so mixed up. It has been calculated that, statistically, you have at least a single water molecule that was in some major player in history such as Shakespeare. This is because so much water went through him and eventually moved throughout the world in the time since then. The same can be said for the early stars.

I hope this helps a little bit

Cuttlefish said...

Oh, it helps tremendously! I knew, but had forgotten completely, about the total replacement of the specific atoms, but that is exactly what I was *trying* to get at with the "Caesar's last breath" bit.

Sounds like we are a puddingstone of atoms from a number of stars--can that number be known within an order of magnitude?--but at least my simplified question is answered: we're not all from "the same star", although we may be from the same puddingstone.

Now, the tough part. How do we know all this? How can we be sure? Can anyone suggest a book that is a relatively friendly yet accurate treatment of the topic?

Cyc said...

A rather good book that goes over this as well as a general history of the universe (as well as what we predict the future of it to be) is "The Five Ages of the Universe" by Professor Fred Adams and Gregory Laughlin. Some of the information is a little outdated (was published in 1999), but in general, it is rather accurate. Another good one that goes into quite a bit more then just this but is a bit more recent is Bill Bryson's "A Short History of Nearly Everything" (2003). This book not only goes into what we know in various fields but how we got to knowing it in the first place.

Cuttlefish said...

The good news is, the latter book is on Cuttleson's bookshelf as we write. So that seems to be the path of least resistance.


Tony said...

Nice post. It's really satisfying to me that my comic could contribute to such an interesting conversation.

I generally agree with most of what Cyc said. When I wrote this comic I was somewhat confused on how star formation works. I had been reading recent research which indicates that our Sun was formed directly from the shock of a supernova passing through a molecular cloud (I believe the evidence is from weird abundances in meteorites). I mistakenly thought that this meant most of our metals came from this single supernova. More likely, the molecular cloud was seeded with metals from many, many, many past supernova. And this particular supernova was just special because it initiated the gravitational collapse that lead to our Sun.

Oh well, that's one of the nice things about writing a comic like this. A lot of times I learn more from my readers than they learn from me!

Another interesting fact is that our Sun is a Population I star, which paradoxically means that it is roughly 3rd generation (astronomers likes to be confusing to keep the riffraff out). Population II stars are roughly 2nd generation, and Population III stars are first generation. As Cyc mentions, this first set of stars would have been very massive and short lived, so we've never observed a Pop III star. The upshot of all this is that even if our Sun really did all come from the expelled material of a single supernova, that material was already processed through a previous generation.

Cuttlefish said...

Thanks for commenting, Tony! I am a bit embarrassed to admit I had not seen your comic before (save for one that PZ posted); now I will be a regular reader, and saw this particular one while reading backward from the current strip. Thank the web-comic competition--or rather, I thank the webcomic competition.

So, now, I learn one more thing (that might be in Cyc's comments, but I didn't pick up on it)--roughly 3 generations? That's it? I mean, yes, countless billions of stars in each generation, and overlapping lifespans, so plenty of raw material, but just 3 generations?

That is so amazing, it makes up for the fact that I really wanted the "same star" version to be the winner. Just for the sheer romantic phrase.

The sane and intelligent commenters here are just the best! (No, DM, I am not including you.)

pgelliott said...

Simon Sigh's Big Bang is an excellent book that covers some of this ground. Also a great history of astronomy and illustration of the scientific method in action.

Kurt said...

This is just an out of the box kind of idea; since we are truly made of "star stuff" wouldn't that make the calcium and carbon, oxygen and etc. older than our grandparents and ancestors? Since the universe was in fact younger when my parents were born, and since everything around me and everything else was basically "created" in the Big Bang, that would undoubtedly conclude that people now are much older "physically" than their predecessors.

I would enjoy some feed back if anyone would like to comment.

Cuttlefish said...

Kurt--first of all, this blog has moved to

Second... the elements that make up our bodies are indeed decades older than the ones that made up our parents' bodies at our age. Of course, the elements that make up our parents' bodies today are decades older than the ones that made up our parents' bodies decades ago. Mind you, decades are an extraordinarily small fraction of the billions of years those particular carbon atoms have been around, so the "older" atoms are functionally identical to the "younger" ones. (with the exception of radioactive decay of unstable elements, it really doesn't matter how old the individual atoms are.)

Your question reminds me of a story about a guide at a museum, who confidently told guests that the universe was "13.7 billion and two years old". Asked how he knew the date so precisely, the guide said that when he was trained for the job, he was informed that the universe was 13.7 billion years old... and, of course, his training was 2 years ago.