Iron spells the end of a star, I think not...

[shmengie]

I've heard a few cosmologists state that once a star (large enough to go bang) makes iron, it goes supernovae.

 

I find that very hard to believe based on distribution of elements.

 

 

Based on that chart, it looks like half the mass of solar system is heavier elements than iron. It is incomprehensible to me that half the mass of our solar system was converted to heavier elements at the moment of supernovae event.

 

Am I really that dense? ( attempt to be phunny )

Edited April 18, 2015 by shmengie

[John Cuthber]

Do you know what a log scale means?

There is roughly ten thousand times as much hydrogen as iron and about ten times as much iron as nickel (the next commonest heavier element than iron)

[pavelcherepan]

I've heard a few cosmologists state that once a star (large enough to go bang) makes iron, it goes supernovae.

 

I find that very hard to believe based on distribution of elements.

 

This has nothing to do with the distribution of elements. The problem is that due to ⁶²Ni (and ^58/56Fe) having the highest nuclear binding energies synthesis of any elements heavier than iron/nickel via fusion is inherently an endothermic process, i.e. it doesn't release energy but consume it. And as a result no normal star in normal circumstances does produce any heavy elements.

 

With the supernova on the other hand there is such a dramatic amount of excess energy that in the final moments of its existence the star manages to produce a bit of very heavy elements too. In fact any element around us that is heavier that ⁶²Ni is a result of a supernova explosion in which case Moby's song "We're all made of stars" makes perfect sense

 

And coming back to your initial question again. Most of stars will produce Fe in some amounts, but few of them will go bada-boom! And it all depends mainly on two things - mass of the star and its metallicity.

 

<Stellar evolution>

Edited April 18, 2015 by pavelcherepan

[swansont]

That doesn't pass the sniff test. The sun comprises most of the mass of the solar system (~99%), and it's mostly Hydrogen by mass.

 

As JC has pointed out, that's a log scale.

[Sensei]

With the supernova on the other hand there is such a dramatic amount of excess energy that in the final moments of its existence the star manages to produce a bit of very heavy elements too.

 

Supernova is producing free neutrons in such amount that unstable isotopes are absorbing neutrons faster than they can manage to decay.

 

http://en.wikipedia.org/wiki/R-process

 

Neutron capture is process in which nucleus has increased mass number by 1 unit.

If newly produced isotope is unstable, it's decaying after a while.

But if new free neutron manage to hit it, it's increased again.

http://en.wikipedia.org/wiki/Neutron_capture

[shmengie]

So to answer my own question, I really am that dense....

 

Think I understand log scale but have difficulty dividing by 10... :-/ (see reference to personal density)

 

Still, there are a lot of elements heavier than iron.

 

My initial analysis of the chart was of by factors of 10, which clarifies to me why iron is suspect. I still find it very difficult to believe iron is cause of novae events.

Edited April 19, 2015 by shmengie

[Greg H.]

I still find it very difficult to believe iron is cause of novae events.

I'm not sure why. There are reams of documents that support the conclusion.

 

Here's a short synopsis on w.pedia. The key concept to keep in mind though, is that fusion of heavier elements requires the consumption of energy, rather than it's production, meaning that the excess energy that is keeping the star balanced against it's own gravity is suddenly (astronomically speaking) not there, allowing the star to collapse further in on itself.

 

Unfortunately, this also causes the star to explode. It is the extreme amounts of energy released during that explosion that allow for the fusion of heavier (and less stable in the case of things like uranium) elements.

[swansont]

 

My initial analysis of the chart was of by factors of 10, which clarifies to me why iron is suspect. I still find it very difficult to believe iron is cause of novae events.

 

Things heavier than iron can't fuse and release energy. Stars run on fusion. When they lose the ability to release energy they collapse, and then there's a catastrophic infusion of fuel into the core, releasing a lot of energy — some of which allows these heavy elements to fuse.

[robinpike]

 

Things heavier than iron can't fuse and release energy. Stars run on fusion. When they lose the ability to release energy they collapse, and then there's a catastrophic infusion of fuel into the core, releasing a lot of energy — some of which allows these heavy elements to fuse.

 

Can the sequence causing the collapse be explained a bit more please?

 

If it is the escaping light that is keeping the atoms in the star hot - and therefore keeping the star from collapse - doesn't light typically take thousands of years (if not millions) to escape from the star?

 

And yet a supernova for a large star occurs as a catastrophic event - how does the collapse happen so quickly?

[swansont]

 

Can the sequence causing the collapse be explained a bit more please?

 

If it is the escaping light that is keeping the atoms in the star hot - and therefore keeping the star from collapse - doesn't light typically take thousands of years (if not millions) to escape from the star?

 

And yet a supernova for a large star occurs as a catastrophic event - how does the collapse happen so quickly?

 

 

http://en.wikipedia.org/wiki/Type_II_supernova

http://abyss.uoregon.edu/~js/ast122/lectures/lec18.html

Light takes a long time to leave the star because it continually scatters off of a dense medium and executes a random walk. The total distance traveled in a random walk is the mean free path times the square root of number of scatters. So if the mean free path is a cm, and the star's radius is 10 million km, then it takes 10^24 scatters to get out. The time between scatters is (mean free path)/c, or 3.33 x 10^-11 sec per scatter. That's about a million years. It's a rough number, since the mean free path depends on wavelength, and for smaller stars it will take less time.

[robinpike]

 

 

http://en.wikipedia.org/wiki/Type_II_supernova

http://abyss.uoregon.edu/~js/ast122/lectures/lec18.html

Light takes a long time to leave the star because it continually scatters off of a dense medium and executes a random walk. The total distance traveled in a random walk is the mean free path times the square root of number of scatters. So if the mean free path is a cm, and the star's radius is 10 million km, then it takes 10^24 scatters to get out. The time between scatters is (mean free path)/c, or 3.33 x 10^-11 sec per scatter. That's about a million years. It's a rough number, since the mean free path depends on wavelength, and for smaller stars it will take less time.

 

Thanks Swansont, those are good links - hadn't really thought about 'electron degeneracy' - always wondered how the star could collapse so quickly.

[Airbrush]

Is uranium the heaviest metal a hypernova can create and be long-lasting?

[swansont]

Is uranium the heaviest metal a hypernova can create and be long-lasting?

There may be an "island of stability" that is heavier, where nuclei may be relatively long-lived, but that's heavy on "relatively".

 

Uranium is the heaviest one known to survive any geologically relevant times.