Expert: Jayendra Upadhye - 6/17/2008

Question
QUESTION: Hi, Jay! I was reading a book called "The Life and Death of Stars", and reading about the seasons, the 231/2 degree tilt of the Earth's axis, which I learned about years ago. But I started thinking, and my question is this: Do scientists have any GOOD theories on HOW the Earth got a 23.5 deg. tilt, and Uranus has a tipped-on-its-side angle of 98 degrees? All the planets have a different axis, are they all results of collisions, in early times?

And one more, if possible. I've read how stars, before a supernova, "burn" Hydrogen and fuse atoms in the core, creating Carbon, Silicon, and eventually Iron, after which they cant create any new elements, and either explode, or become dwarfs, or Neutron Stars. What I don't understand, is, After the Sun formed itself, it threw off blobs of Hydrogen, as a Hot, new star. But the Earth, the Moon, Venus, Mars, are made mostly of rock, silicon, and Iron, copper, gold, uranium, aluminum, boron, all the metal and non-metal elements! WHERE did all these 110 elements COME FROM? I mean, even supernovas don't create all those, right? And obviously, our young sun wasn't a Supernova, or we wouldn't BE here? I'm just trying to understand, WHERE did all the Elements COME FROM?   I appreciate any help you can give.
         Thanks in Advance,   Mike

ANSWER: Hi Mike!
No! The sun is a 3rd generation star.
Like the phoenix, it arose from the debri of earlier supernovas.
What happens is that in the supernova progenitor, once iron formation starts, the process being endothermnic, it saps the core of energy very quickly, effectively cooling it off. This makes the core "shut down" and the overlying layers try to maintain thermodynamic equilibrium by contraction and crushing the core making its temperature rise again. This is a runaway process.
The core implodes in seconds, shrinking from say the size of 3-4 solar radii to that of a few scores of kilometers.
It rapidly evolves into a diamond hard (or say neutron hard) newurton star. The incoming overlying layers fall on this and rebound. The outbound shockwave sometimes punches thru the inbound overlying layers, and emerges after a day or two. That is the supernova explosion we see. If the shock stalls, we see what happened to Eta Carinae a cataclysmic variable star. The star retains integrity, but lets of powerful solar winds that carry of most of the outlying layers.
The shock triggers the formation of all trans iron elements.
It is these that are the leftovers of previous supernovae around the nursery where the sun formed, that gave us all the trans-hydrogen elements we see around us today. The carbon, iro, water, silicon, iron, uranium all are star stuff more ancient than our sun that even now has just graduated to cooking up helium the second element of the periodic table!

hope that suffices.
Please do rate the answer if you find it helpful
Jayen

---------- FOLLOW-UP ----------

QUESTION: Hi again, Jayen. Thanks for responding. I can tell you're very knowledgeable about supernovae, and element creation, so I hope you can help me understand this. I think I understand the basics of a supernova expolsion, I have a few books on the subject. I understand the compression of the core, the collapse due to gravity, shock waves, the fusing of protons and atoms, the creation of elements, up to iron. But the books I have say that when the core "gets to" iron, it can't make any new elements after iron, and either a Massive star goes supernova, or a smaller one becomes a dwarf, or neutron star.
I don't quite understand what you mean, by "trans-iron", or "trans-hydrogen". What I was specifically trying to understand, was my gap in the knowledge of HOW the Elements "beyond" Iron are created, if stars cannot "fuse" any new Elements PAST Iron! I read where you said our Planets are from more ancient supernovae, but I STILL don't understand HOW THOSE ELEMENTS ARE CREATED. What is the PROCESS, by which Gold, Uranium, tungsten, are created, if Stars cannot "burn" new Elements beyond Iron?

I read your whole answer, but the part where you wrote:
"The shock triggers the formation of all trans iron elements.
It is these that are the leftovers of previous supernovae around the nursery where the sun formed, that gave us all the trans-hydrogen elements we see around us today. The carbon, iro, water, silicon, iron, uranium all are star stuff more ancient than our sun that even now has just graduated to cooking up helium the second element of the periodic table!" , wasn't really clear, for my reasons above.
I knew, obviously, that our sun has NOT gone supernova, so the silicon and Iron that the Earth is made up from CANNOT be from our Sun! But 1.)Why do science books say that the Planets were matter "thrown off" by the Sun's early formation, and 2.)You say that the Uranium, Gold, Lead, and even less dense elements, like lithium and boron, for example, were formed by "Ancient Star stuff". But HOW were these elements formed? The science books say there is a process: 1. Hydrogen 2. Helium 3.Carbon 4. Silicon 5. Iron, and after IRON, the star's core cannot make any NEW elements? So HOW are the other 105 created?

I hope I've been a little clearer, this time, in what I'm trying to understand. I really appreciate you sharing your knowledge with me. I've always been the type of person that strives to Understand the Mysteries of Science, physics, the Universe. If I don't understand the "hows" or "whys" of something fundamental to our existence, I'm like a dog with a bone, I can't let go, until I DO understand.  Thanks again, Jay.  

Answer
Hi Mike!
hehe..Dog with bone...thats why I said we are the same type..well almost that is, i let go a wee bit earlier than you!!

You are more persistent i think, which is all the more creditable.

Coming to your question,
So we do agree that all "trans hydrogen" meaning elements beyond hydrogen, in the periodic table do come from more ancient supernovas around the solar nursery.

Now the trans iron part.
please refer to the type 2 spernovas in para "Source of heavy elements" in the site http://en.wikipedia.org/wiki/Supernova

As i mentioned previously, it is the stalled shock wave within the rebounding matter that creates trans-iron elemets (gold silver, uranium, you name it), by nucleosynthesis in the high temperature high nutron abundance environmemt of teh shock.
Further, the chock front is re-invigorated by nuetrino capture and Gamma ray flux from the core(the r process).
There is another lower energy process, (s process) which cannot progress beyond formation of lead.

Regarding the "How" for the r and s processes, I havent the foggiest!!
(one must acknowledge that one does not know...remember?)

So now you know my limits..i have bottomed out..etc. :)

You may need other experts from here on further...but then one must ask only what one will understand!!

You would be totally at sea (me included) if some thermodynamics guy opened his bible and started his sermon on magnetohydrodynamics and kinetic theory!

But then that would be a different forum too!

regards
Hope that suffcies, please do rate the answer if you found it meaningful.
Jayen