The Sun is a Third-Generation Star. The First Two Were...

[On the Road]

(Original title: Study: Universe Lifeless After Big Bang)

ATLANTA - The first stars after the Big Bang were immense, superhot giants that lived briefly and then exploded as brilliant supernovae, but they seeded the universe with basic elements that were the building blocks for the sun and the Earth, and for life itself, according to a new study.

---snip

Those early stars were immense, extremely hot and very short-lived. After just a few million years, they collapsed and exploded as supernovae. In that violence were created the heavier elements "that completely changed the universe," said Bromm. Elements from oxygen to carbon to iron were blasted into space where they eventually became part of a new generation of stars.

---snip

Supernovae continued to explode, seeding the universe with more and more heavy metals. Eventually, there were enough of these metals to create long-lived stars and for planets to accrete into their orbits. On at least one planet, the Earth, all the ingredients came together in the right place and time for life to evolve. "The window for life opened sometime between 500 and 2 billion years after Big Bang," Loeb said in a statement.

http://story.news.yahoo.com/news?tmpl=story&cid=514&e=8&u=/ap/20040107/ap_on_sc/life_from_stars


This is really something. I always wondered where all those heavy elements came from.

[Kolesar]

1. "We are all...star stuff" --Carl Sagan

I think I got that quote right. Stars are nuclear reactors that turn hydrogen into heavier elements through successive transformations.

[On the Road]

2. Yes, But at Some Point

those heavier elements had to escape in order to form planets and other solid bodies. The first two generations of starts both created the elements and, when they exploded, distributed them over the universe.

[pmbryant]

3. Interesting model, albeit not exactly new

Thanks for posting the article about it. :-)

The multi-generational aspect of stars has been understood, at least a very general form, for decades. Of course, it is a vast over-simplification, but a useful one in many ways.

--Peter

[On the Road]

4. Well, It Was New to Me

I only dabble. But it makes a lot more sense of the way the universe is distributed.

[NNadir]

5. This is relatively well known.

Stars synthesize all of the heavy elements, but not all stars synthesize all elements.

It turns out that you can release energy by fusing light elements so long as the fusion product is lighter than iron. Iron has exactly the optimal binding energy/mass balance.

Normal stars synthesize elements higher than iron by a process known as the s (slow) process, wherein elements absorb protons (and energy) or neutrons to give heavier elements. Since the process consumes energy rather than release it, this has the effect of actually cooling a star. This process in light stars, such as the sun yields some heavier elements. Elements like Tin, Molybdenum, Palladium, and Silver may be formed in this way.

The vast majority of the heaviest elements, including Uranium, Thorium, as well as elements such as Platinum, Gold, Mercury and Lead result from the explosions of supernovae in what is called the r (rapid process), in which an enormous flux of accelerated nuclei fuse at an enormous rate during the fast collapse of a massive star. (Elements heavier than Bismuth are generally not accessible by the s process owing to the physics of these nuclei.) When the star subsequently explodes the universe is seeded with heavy elements. It is probable that most of the elements found on earth are supernovae ejecta. I recall reading a paper sometime ago that indicated that it is believed that as many as eight supernovae are represented in the earth's elemental balance.

Traces of the long-lived isotope of Plutonium, Plutonium-244, with a half life of about 80 million years, have been found in California Thorium bearing rocks. It is believed that this Plutonium may be remains of plutonium found on the early earth, although formation by cosmic radiation has not been rigorously excluded. It seems likely that Plutonium was none the less present for a few billion years of earth's history. Curium-247, with a half-life of 15,600,000 years also may have lasted long enough to accrete in the protoearth. Except for a few atoms here and there, all of the supernovae plutonium-244 has now decayed to (radioactive) Thorium-232 and its daughters, and all of the Curium-247 is now represented as Uranium-235 and its daughters.

Three light elements do not survive long enough in stars to be found in great abundance in their ejecta. These are beryllium, boron, and lithium. Beryllium-8 is probably the shortest lived nuclei known because it can easily fission to give two the extremely stable helium-4 nuclei. Beryllium, Boron and Lithium are generally consumed far faster than they are formed. Lithium and Boron have interesting nuclear properties, including the fact that they are, along with nitrogen, odd numbered elements to have two isotopes that differ by only one mass number.

(Boron-10 and 11, Lithium 6 and 7 and nitrogen 14 and 15 represent these pairs - Nitrogen 14 is the only nucleus known that is stable while having both an odd number of neutrons and protons. No stable nucleus exists with a mass number of 8. Beryllium has only one stable isotope, Beryllium-9.)

In fact the non existance of a stable nucleus of mass 8 is a problem in stellar elemental synthesis, overcome only when three helium-4 collide to give carbon-12. Nuclear synthesis must "leap-frog" over this barrier of 8 by means of this very improbable reaction that probably takes place only in dense stellar cores.) All of the Beryllium, and boron on earth probably was formed in interstellar clouds by interaction of cosmic radiation with heavier nuclei by a process known as spallation. Much of the lithium was probably aslo formed in this way, although a significant portion of the lithium-6 in the universe may be an artifact of the big bang. This accounts for the relative rarity of these elements.

Carbon-12 plays a catalytic role in hydrogen burning in ordinary stars. It is faster to burn hydrogen in the presence of carbon-12, through a process known as the carbon cycle, than it is to fuse two hydrogen nuclei to give deuterium.

[On the Road]

8. NNadir, I Have Another Question

If heavier elements are formed in stars and scattered, what accounts for the fact that elements on earth are rarely found evenly distributed, but in clumps? I learned how metals would cluster because of they way they share electrons, but it would seem like almost all elements would do this, at least in solid form, or the chemical composition of the earth's crust should be much more uniform than it is.

[NNadir]

9. The distribution of elements results from chemical and physical processes.

During the condensation of planets from diffuse matter in clouds, the elements are probably widely and nearly evenly distributed. One a planet condenses however, a multitude of other processes can occur to fractionate the elements.

If a planet for instance condenses in such a way that it's atmosphere contains hydrogen sulfide gas, this gas will react with iron (and other transition metals) to form insoluble sulfides. This will effectively separate (in the presence of water) iron from sodium and calcium. The local area in which this precipitation occurs will be in effect, an iron ore. (Much of the iron found and mined on earth is in fact the sulfide.)

Another process that takes place is weathering. Rocks that contain diffuse amounts of Gold (a dense element, will have the Gold concentrated because it is dense and chemically unreactive. It tends to stay where it is, while the other elements are washed away.

Other physical processes that result in element concentration include heating and cooling, as at undersea hydrothermal vents. Compounds of elements may be very soluble in hot water but may crystallize out in cooler water. Many hydrothermal vents are surrounded by high quality ores of various metals.

Biological actions are also important in ore formation. Many plants and animals tend to concentrate certain elements. The element phosphorous was historically mined from certain islands where it was present in high concentrations in bird guano. Many other species concentrate many other elements.

Many times these physical and chemical processes repeat over and over, each time resulting in greater and greater fractionation of the elements, resulting in very high quality ores. Sometimes the separations only result in partial fractionation into chemical groups. The element Zirconium is never found without it cogener Hafnium in naturally occurring ores, because the chemistries of these two elements are nearly identical. Indeed the difficult separation of Zirconium from Hafnium was one of the greatest technical problems in building the nuclear industry, since Hafnium absorbs neutrons while Zirconium does not. (Zirconium is the element of choice for building nuclear reactor cores.)

Many elements never concentrate in quantities that are sufficient to make good quality ores. Scandium, a potentially very useful element represents such a case. Though it is widely distributed, it seldom concentrates in any mineral. Thus it has no economically important uses, though it apparently would represent an excellent element for the construction of aircraft.

One factor that is necessary for the concentration of ores is a geologically active planet with mobile (liquid) phases such as earth.
Without these conditions, the elements remain diffuse and difficult to isolate.

[gate of the sun]

6. I wondered as well

when I took chemistry in college.Where all the elements came from.

[progressivejazz]

7. Awe inspiring.

The thought that nearly all of my body is made up of stuff that was once exploded out of stars so far away fills me with awe.

That this stuff has arranged itself in such a way that I am able to ponder this issue is even more stunning.

I find this much more awe-inspiring than the insipid "God did it". Maybe so; but if so, it appears God did it this way.