How Old Are Our Atoms – How Many Stars Made Them?

Is there any way to estimate how long ago the atoms in our solar
system were made and how many generations of stars came before ours?

I'm asking here about atoms like Carbon. The carbon in our solar
system, in our planet, and in our bodies was made in stars like our
own. Right? Is there any way to make even a broad ballpark estimate
of how long ago this carbon was made and by how many stars?

One of the reasons I started thinking about this was that I read
somewhere that a star like our Sun has a lifespan of nearly 10 billion
years. That's more than 50% of the age of the Universe. So what I'm
getting at is that it doesn't seem like there could have been very
many generations of stars before our own began to form. Yet we have a
real abundance of elements here. I'm having trouble understanding how
so many atoms were made so relatively fast. Now, I understand that
larger stars burn out more quickly and that the first stars in the
universe would have been truly enormous. That helps a bit. But on the
other hand, some elements like for example Florine and Platinum are
not made by any kind of star, but by really exotic processes like the
collision of two neutron stars.

So, getting back to the question. About how long ago were the atoms
we see today made? Is there any way to estimate such a thing? Maybe
the opposite question is easier to answer. About how long after
Betelgeuse goes supernova will the atoms it has made find their way
into new solar systems?

Post a follow-up to this message

Eric wrote:
Is there any way to estimate how long ago the atoms in our solar
system were made and how many generations of stars came before ours?

I'm asking here about atoms like Carbon. The carbon in our solar
system, in our planet, and in our bodies was made in stars like our
own. Right? Is there any way to make even a broad ballpark estimate
of how long ago this carbon was made and by how many stars?

If you look at any particular atom of carbon--no, you can't tell.
There are three isotopes of carbon that will hold together to any
extent: carbon-12, carbon-13, and carbon-14, of which only carbon-14
is radioactive (and famously so). Each has six protons, but they
have differing numbers of neutrons (6, 7, and 8, respectively).
Aside from that, however, there is nothing I can think of that
distinguishes any carbon atom in isolation from any other.

It is possible to date once-living material (such as a tree trunk)
using the radioactive property of carbon-14. Living things constantly
exchange carbon with the surrounding environment, so until they die,
the proportion of carbon-14 to carbon-12 in the organism remains
relatively constant. Once the organism dies, however, no more carbon-14
can be taken in, and the proportion of carbon-14 drops gradually but
steadily. An estimate of the time since the organism died can be made
by measuring the carbon-14 to carbon-12 ratio. (Carbon-13 is a rare
stable isotope and can be ignored for these purposes.)

However, because the half-life of carbon-14 is so short, astronomically
speaking, it can't possibly be left from the original assembly of our
solar system. It has to be made constantly somehow, and in fact, it
is created by cosmic rays striking atoms in our atmosphere. The amount
of carbon-14 is a reflection of a steady state between the continual
decay of carbon-14 and its creation by cosmic rays.

One of the reasons I started thinking about this was that I read
somewhere that a star like our Sun has a lifespan of nearly 10 billion
years. That's more than 50% of the age of the Universe. So what I'm
getting at is that it doesn't seem like there could have been very
many generations of stars before our own began to form.

It turns out that the lifespan of stars is strongly dependent on their
initial mass. Very roughly speaking, the luminosity of a star is
proportional to its initial mass raised to the 3.5th power. Just to
give an example, a star with just twice the initial mass of the Sun
will shine much brighter than the Sun, by a ratio equal to 2 raised to
the 3.5th power--about 11 times. That luminosity can't come from
nowhere; it has to come out of the total energy budget of the star,
which is only roughly proportional to its mass. Since the star has
only twice the energy to shine 11 times as bright, its lifespan will
be less than 1/5 that of the Sun: about 2 billion years.

Conversely, a star with only (say) 1/4 the mass of the Sun--a red dwarf,
in other words, the most common type of star in the galaxy--will shine
with only 1/128 the brightness, and will therefore last about 30 times
as long: a third of a trillion years.

Although most of these stars haven't perished, there are enough stars
that are more massive than the Sun that have perished to furnish the
galaxy with so-called "metals." (To an astronomer, a metal is simply
any element more massive than hydrogen and helium. Carbon is a metal
to them.) It doesn't hurt that these more massive stars have more to
give in the first place.

Even so, the proportion of heavy elements is small by ordinary standards.
Most stars are less "metallic" than the Sun, yet the Sun's metallicity
is on the order of 1 or 2 percent. The overwhelming majority of the Sun
is still hydrogen and helium. We notice the other elements because the
Earth isn't massive enough to hold onto the hydrogen and helium in their
elemental state. Hydrogen can only be maintained in molecular form as
in water. Helium is only found in gaseous form (in the natural world)
and is formed largely as a by-product of uranium decay.

The upshot is that although these heavier elements are rare, they
don't have to be very high in concentration before they can make worlds.
The Sun is large enough that even a tiny fraction of the heavier
elements is more than sufficient to make the Earth and the other
planets.

So, getting back to the question. About how long ago were the atoms
we see today made? Is there any way to estimate such a thing? Maybe
the opposite question is easier to answer. About how long after
Betelgeuse goes supernova will the atoms it has made find their way
into new solar systems?

Tough question. It depends on what triggers solar system formation, a
process we are still in the early stages of understanding. The elements
are dispersed into the interstellar medium more or less instantly, but
it then takes a large and effectively random time before some event
(perhaps the explosion of another supernova) serves to compress a segment
of that medium into a new solar system.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

eric wrote:

Is there any way to estimate how long ago the atoms in our solar
system were made and how many generations of stars came before ours?

I'm asking here about atoms like Carbon. The carbon in our solar
system, in our planet, and in our bodies was made in stars like our
own. Right? Is there any way to make even a broad ballpark estimate
of how long ago this carbon was made and by how many stars?

One of the reasons I started thinking about this was that I read
somewhere that a star like our Sun has a lifespan of nearly 10 billion
years. That's more than 50% of the age of the Universe. So what I'm
getting at is that it doesn't seem like there could have been very
many generations of stars before our own began to form. Yet we have a
real abundance of elements here. I'm having trouble understanding how
so many atoms were made so relatively fast. Now, I understand that
larger stars burn out more quickly and that the first stars in the
universe would have been truly enormous. That helps a bit. But on the
other hand, some elements like for example Florine and Platinum are
not made by any kind of star, but by really exotic processes like the
collision of two neutron stars.

So, getting back to the question. About how long ago were the atoms
we see today made? Is there any way to estimate such a thing? Maybe
the opposite question is easier to answer. About how long after
Betelgeuse goes supernova will the atoms it has made find their way
into new solar systems?


Main Sequence Lifetimes
http://www.mhhe.com/physsci/astronom...r19/19f09.html
All stars the mass of our Sun and greater create carbon in their
helium burning phases, So there was plenty of carbon created and
swept up into out solar system when it formed some 4.6 billion years
ago.

All of the hydrogen (and much of the helium) is 13.7 billion years old.
Elements up through the iron group are synthesized in the fiery cores of
massive stars. The more massive elements in supernovae explosions.

For some resource material see:
http://www.cnde.iastate.edu/staff/sw...te_dwarfs.html
http://www.cnde.iastate.edu/staff/sw...ack_holes.html

When looking at the Universe about us:

o We find mostly hydrogen and helium. Why--we have compelling
evidence drawn from many corners of astronomy and physics that
the universe evolved from a hotter dense state. When one models
the hotter denser state of about the first few hundred seconds,
particle physics predicts that roughly 75% hydrogen and 24%
helium will be formed from the primordial soup. Observation
confirms these abundance's.

o We have a good understanding of nucleosynthesis of elements
through the iron group, including carbon, nitrogen and oxygen.
I refer you to to Lang (1999), "Astronomical Formulae Vol. I",
Sec 4.4, "Nucleosynthesis of the Elements", pp 402-432.

o We have some understanding of creation of elements with atomic
number greater than the iron group. The computing power and
detail during the relativistic collapse of stellar structures
is a tough problem for details... no hint whatsoever that these
processes are incorrect for the nucleosynthesis of the observed
heavier elements.

Ref: "Astronomical Formulae" Lang 1998 pg 103

"We now realize that elements heavier than iron cannot be
produced in successive static burning stages within stars.
This is because any nuclear reaction involving the iron
group of nuclei, with atomic weight A ~ 56, cannot provide
fuel for the thermonuclear fires that support a star and make
it shine. Instead, the iron-group elements act like seeds for
the synthesis of heavier elements by neutron capture. Such
processes were first suggested by George Gamow for nonequilibrium
nucleosynthesis during the early stages of the expansion of
the Universe (Gamow, 1948; Alpher, Bethe and Gamow, 1948), and
applied to the later stages of stellar evolution by Burbidge,
Burbidge, Fowler and Hoyle (1957), often called B²FH, and
independently by Cameron (1957)".

"Double-peaked features in the abundance curves Relative Abundance
vs Atomic Weight] (Fig. 5.27) indicate that two neutron capture
processes, called the r-process and the s-process, must synthesize
elements with atomic weights A greater than 60. The rapid (r- process)
neutron capture occurs on time scales of about 100 seconds, which
is rapid (r) compared to electron beta decay in the synthesis
networks, while the s-process is much slower (s), occurring over
scales of 10² to 10^5 years. All naturally occurring radioactive
elements with A 209, including the long-lived uranium, U, and
thorium, Th, parents, 238U, 235U and 232Th, require the r-process,
which builds beyond mass 238 to nuclei that decay back to these
radioactive parents. The r-process probably occurs during stellar
explosions, called supernovae, that rapidly provide a large neutron
flux with a short duration".

(eric) wrote in message om...

Is there any way to estimate how long ago the atoms in our solar
system were made and how many generations of stars came before ours?

Well, one popular theory is that most star formation is triggered
by pressure waves from supernovae. In that case, a significant
chunk of the stuff our solar system is made of might have come
from that very same supernova, and be only slightly older than
the Sun itself. Of course, the Sun is also constantly
synthesizing new atoms, so in that sense, some of the atoms are
very young indeed. Note that carbon, nitrogen, and oxygen
participate in a cycle which leads to no net increase of
any element, but where any given nucleus may be churned
through the cycle many times.

However, that supernova itself was not a first-generation star,
or anywhere near it. As Brian says, massive stars burn out in
a hurry, much faster than the Sun, and it takes a pretty massive
star to make a supernova. So the first wave of heavy-element
creation must have happened shortly after the galaxies started
to form, very early in the life of the Universe. And no doubt
some of those atoms are also in our Sun.

I am sure that some people would be willing to venture guesses
about the proportions of atoms of various ages, but you don't
necessarily have to take them too seriously. One of the joys
of astronomy is just how much isn't known ...

- Tony Flanders

Sam Wormley wrote:
For some resource material see:
http://www.cnde.iastate.edu/staff/sw...te_dwarfs.html
http://www.cnde.iastate.edu/staff/sw...ack_holes.html

Those links appear to be broken.

James Goldman wrote:

Sam Wormley wrote:
For some resource material see:
http://www.cnde.iastate.edu/staff/sw...te_dwarfs.html
http://www.cnde.iastate.edu/staff/sw...ack_holes.html

Those links appear to be broken.

Oops!
http://edu-observatory.org/eo/white_dwarfs.html
http://edu-observatory.org/eo/black_holes.html

(Tony Flanders) wrote in message m...
(eric) wrote in message om...
Is there any way to estimate [1] how long ago the atoms in our solar
system were made and [2] how many generations of stars came before ours?
snip

Eric - As to your first question on how long ago the atoms in the our
solar system were made, a well-reasoned answer on this one can be
found in Ned Wright's Cosmology tutorial at:

http://www.astro.ucla.edu/~wright/age.html

Wright's answer is that although the ratio of some isotopes in rocks
in the Earth have been used to date the age of the Earth at around
4.65 billion years, --

==============
Quote from Wright's Cosomology page
==============
[w]hen applied to a mixed together and evolving system like the gas in
the Milky Way, no great precision is possible. . . . This requires
that we know precisely how much of each isotope was originally
present, so an accurate model for element production is needed. [

]One isotope pair that has been used is rhenium and osmium: in
particular Re-187 which decays into Os-187 with a half-life of 40
billion years. It looks like 15% of the original Re-187 has decayed,
which leads to an age of 8-11 billion years. But this is just the mean
formation age of the stuff in the Solar System, and no rhenium or
osmium has been made for the last 4.56 billion years [in the Solar
System]. Thus to use this age to determine the age of the Universe, a
model of when the elements were made is needed. If all the elements
were made in a burst soon after the Big Bang, then the age of the
Universe would be to = 8-11 billion years. [

]But if the elements are made continuously at a constant rate, then
the mean age of stuff in the Solar System is

(to + tSS)/2 = 8-11 Gyr

which we can solve for the age of the Universe giving

to = 11.5-17.5 Gyr

==============
End quote
==============

You can't talk about the age of a particular atom - although you can
talk about the average statistic age of one element in the Earth's
crust.

Some rhenium, for example, might have been created relatively recently
- say by a short-lived massive "O" class star (average life 120
million years) that went supernova 4.75 billion years ago. Some
rhenium might have been created in a long-lived "G" class star
(average life 11 billion years), that was created near the begining of
the universe started expelling large quantities of elements into the
stellar wind, in its red giant phase, after 8 billion years, but at
4.75 billion years ago.

The gasous elements expelled from both stars mixed and eventually were
incorporated into the molecular cloud that created the Earth 4.65
billion years ago, eventually being incorporated into a rock on the
terrestial surface. The average age of all these contributors of
rhenium, statistically, is 8-11 billion years ago.

So it looks like the answer is, for the element rhenium, that the
_average_ age of all the rhenium in the Earth is between 8-11 billion
years old. Rhenium is not involved in any biological processes.

Unfortunately, you can't make the kind of estimate of the average age
shown with rhenium with the biologically active elements that you are
made of - oxygen, carbon and nitrogen. Carbon_14 has a half-life of
only 5730 years; oxygen and nitrogen and their istopes are stable.

Regards - Kurt