(Caption) Supernova remnant G1.9+0.3 (Combined image from Chandra Xray data and radio data from NRAO's Very Large Array). Credit: http://chandra.harvard.edu

Astronomy Without A Telescope – Alchemy By Supernova

14 Aug , 2010 by

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The production of elements in supernova explosions is something we take for granted these days. But exactly where and when this nucleosynthesis takes place is still unclear – and attempts to computer model core collapse scenarios still pushes current computing power to its limits.

Stellar fusion in main sequence stars can build some elements up to, and including, iron. Further production of heavier elements can also take place by certain seed elements capturing neutrons to form isotopes. Those captured neutrons may then undergo beta decay leaving behind one or more protons which essentially means you have a new element with a higher atomic number (where atomic number is the number of protons in a nucleus).

This ‘slow’ process or s-process of building heavier elements from, say, iron (26 protons) takes place most commonly in red giants (making elements like copper with 29 protons and even thallium with 81 protons).

But there’s also the rapid or r-process, which takes place in a matter of seconds in core collapse supernovae (being supernova types 1b, 1c and 2). Rather than the steady, step-wise building over thousands of years seen in the s-process – seed elements in a supernova explosion have multiple neutrons jammed in to them, while at the same time being exposed to disintegrating gamma rays. This combination of forces can build a wide range of light and heavy elements, notably very heavy elements from lead (82 protons) up to plutonium (94 protons), which cannot be produced by the s-process.

How stuff gets made in our universe. The white elements (above plutonium) can be formed in a laboratory, but it is unclear whether they form naturally - and, in any case, they decay quickly after they are formed. Credit: North Arizona University

Prior to a supernova explosion, the fusion reactions in a massive star progressively run through first hydrogen, then helium, carbon, neon, oxygen and finally silicon  – from which point an iron core develops which can’t undergo further fusion. As soon as that iron core grows to 1.4 solar masses (the Chandrasekhar limit) it collapses inwards at nearly a quarter of the speed of light as the iron nuclei themselves collapse.

The rest of the star collapses inwards to fill the space created but the inner core ‘bounces’ back outwards as the heat produced by the initial collapse makes it ‘boil’. This creates a shockwave – a bit like a thunderclap multiplied by many orders of magnitude, which is the beginning of the supernova explosion. The shock wave blows out the surrounding layers of the star – although as soon as this material expands outwards it also begins cooling. So, it’s unclear if r-process nucleosynthesis happens at this point.

But the collapsed iron core isn’t finished yet. The energy generated as the core compressed inwards disintegrates many iron nuclei into helium nuclei and neutrons. Furthermore, electrons begin to combine with protons to form neutrons so that the star’s core, after that initial bounce, settles into a new ground state of compressed neutrons – essentially a proto-neutron star. It is able to ‘settle’ due to the release of a huge burst of neutrinos which carries heat away from the core.

It’s this neutrino wind burst that drives the rest of the explosion. It catches up with, and slams into, the already blown-out ejecta of the progenitor star’s outer layers, reheating this material and adding momentum to it. Researchers (below) have proposed that it is this neutrino wind impact event (the ‘reverse shock’) that is the location of the r-process.

It’s thought that the r-process is probably over within a couple of seconds, but it could still take an hour or more before the supersonic explosion front bursts through the surface of the star, delivering some fresh contributions to the periodic table.

Further reading: Arcones A. and Janka H. Nucleosynthesis-relevant conditions in neutrino-driven supernova outflows. II. The reverse shock in two-dimensional simulations.

And, for historical context, the seminal paper on the subject (also known as the B2FH paper) E. M. Burbidge, G. R. Burbidge, W. A. Fowler, and F. Hoyle. (1957). Synthesis of the Elements in Stars. Rev Mod Phy 29 (4): 547. (Before this nearly everyone thought all the elements formed in the Big Bang – well, everyone except Fred Hoyle anyway).



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ILOVETHESTAR
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ILOVETHESTAR
August 14, 2010 6:01 PM

I would love to hear Hon. Saculous B Crumb interpretation of a simple detonation of a type Ia supernova and what elements are created-and spread throughout the Universe. His interpretation is very clear to me. Most other interpretations I’ve read are confusing to me. I am always very interested in this very unusual and very rare event.

ILOVETHESTAR
Member
ILOVETHESTAR
August 14, 2010 6:15 PM

Assuming the typical Type Ia supernova is Mv= -19.3, settting it to the distance of Alpha Centauri would be ~ -23.5 and a distance of 3260LY -9.3, I hope to see a type Ia supernova within 5000LY in my lifetime.

Lawrence B. Crowell
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Lawrence B. Crowell
August 14, 2010 6:40 PM

I find it odd that Li, Be and B are formed from cosmic rays. I should think that very little of these elements would exist. I think some Li was generated in the big bang. Yet these elements are relatively common.

LC

HeadAroundU
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August 14, 2010 7:13 PM

So why didn’t Big Bang create heavy elements? Was it all quarks or what?

Lawrence B. Crowell
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Lawrence B. Crowell
August 14, 2010 8:05 PM
@HeadAroundU : This is largely because the time period where temperatures in the big bang were in the right range to cook up heavy elements lasted a few seconds. It was also not a period of implosive pressure as in the interior of a collapsing star, but a time where material was expanding outward. So the period of equilibrium for p + n –> D was brief and far to short to cook up heavier elements. It is possible that a few carbon nuclei, maybe an iron or lead nucleon here and there were cooked up out of 10^{30} or 10^{40} nucleons (protons, deuterium and helium). However, largely deuterium and helium were all that emerged from big bang… Read more »
Lawrence B. Crowell
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Lawrence B. Crowell
August 14, 2010 8:08 PM

Steve is right, and for some reason I said seconds, when I should have said minutes.

LC

jimhenson
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jimhenson
August 15, 2010 6:49 AM

the big-bang could resemble a self-similar quantum field effect supernova event horizon collision explosion that formed hierarchial fractal scale patterns from atoms, stars, galaxies etc. everywhere still today. each scale has intrinsically a brief period of time relativity that heavier elements can form until expanding cooling beyond further allowable conditions. The fact that the LHC is colliding particles like in a stars reactor, to study big-bang conditions, and claiming to search for the higgs boson and god particles, indicates that the universe is a quantum effect big-bang.

jimhenson
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jimhenson
August 15, 2010 9:38 AM
Jackson says both the early mantle and the Baffin Island lava rocks, have tell-tale neodymium isotopes that are unlike chondrites. Also a very old lead isotope signature and helium 3 levels were found. So the moon did not come from the earth by a collision. The moon has one ten thousandeth 1/10,000 the total Hydrogen content of the earth by recent measurements showing its devoid of water unlike the earth in early solar system formation. Up to 10 percent holy grail lava basalts might still exist on earth, found in non-geothermal void spaces between tectonic plates, and not uplifted from hot spots that melt rocks. Preservation beneath permanent canadian glacier ice caps and being deeply beneath the surface… Read more »
Olaf
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Olaf
August 15, 2010 3:20 AM

During the big bang the first particles moved at relativistic speeds. Did this have any effect on the forming event of the Big bang? For example weighing more heavy and time dilation?

HeadAroundU
Member
August 15, 2010 4:30 AM

Thanks for answers.

So, only 17 minutes for a slow process.

LC, you mean iron or lead nukleus, right? Nucleons are only protons and neutrons.

Aqua4U
Member
August 15, 2010 5:35 AM

Every picture tells a story….

Aqua4U
Member
August 15, 2010 6:01 AM

The caption in the image above that says the most, is: “Nuclear burning occurs at the boundaries between zones.” aka… pressure/density stratification in the magnetically and gravitationally constrained expanding fusion plasma(s).

This says little about ‘cold flow’ plasmas or those plasmas which are magnetically constrained but not restricted to a gravitationally confined condensate which may indicate weak force interactions within the nuclear force via electromagnetically enhanced confinement. ‘Cold flow’ in this case being temperatures below the minimum temperature required for the fusion of hydrogen at 5 million degrees.

Lawrence B. Crowell
Member
Lawrence B. Crowell
August 15, 2010 6:07 AM

HeadAroundU
Yes I meant nuclei, I was a bit tired when I wrote that and kept making slips.

LC

The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
August 15, 2010 7:07 AM
Steve Thank you for this excellent UT story on stellar evolution and nucleosynthesis by-products. It is a good summary of the current level of knowledge on this interesting subject, which frankly I have trouble faulting. (If I were to be honestly critical, the presentation might be just a tad too complex for the average reader here – perhaps trivial in some respects. Of course, the main products being made are mostly formed in ordinary stars and not so much in supernovae – though most elements heavier than 56 Iron are certainly made in these catastrophic events. One particular issue that I find more interesting is the distribution and numbers of each of the element’s isotopes. Knowledge of these… Read more »
The Eclectic Exterminator of Stupid Electricians
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The Eclectic Exterminator of Stupid Electricians
August 15, 2010 7:14 AM

NOTE: There is an interesting story available on AstronomyOnline.org which might interest some UT reader. The article is Nodelling Core Collapse Supernova by Alex Nervosa.

This gives an excellent picture of the theoretical and observational evidence of nucleosynthesis models. Highlighted text within the section “Nucleosynthetic Chemical Yields & Mass Ejection” gives a good deeper explanation of the UT story here.

The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
August 15, 2010 7:43 AM
LBC said; “I find it odd that Li, Be and B are formed from cosmic rays. I should think that very little of these elements would exist. I think some Li was generated in the big bang. Yet these elements are relatively common.” I disagree. In relative abundances, Lithium (actually Li-7) is still fairly rare among the distribution of elements. This primordial lithium after a star is formed is rapidly destroyed and therefore is near impossible to exist from shining stars to supernovae. However, lithium stars (or more properly; lithium-line stars) do exist. I.e The 8.9 magnitude star HIP 99423 / HD 345957 in Vulpecula (Weird Spectral Type of G0Vw ) A technical arVix paper by C.Charbonnel, F.Primas… Read more »
Torbjorn Larsson OM
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Torbjorn Larsson OM
August 15, 2010 8:00 AM
Wow! Let me say that again: wow! That is quite possible the most poignant and beautiful picture I’ve seen! (I.e., in the last months, seeing as how our minds work. ) It was also quite easy to understand the illustrated bounce back symmetry inside the earlier ejecta from the text and the reference. (Its fig 1, especially the more symmetric right column.) Thank you, Steve! People here have hashed out nucleosynthesis to everyone’s satisfaction I think. A datum I seem to remember is that big bang (BB) nucleosynthesis lithium used to be considered deficit in old (pop I ?) stars by a factor 2 or so, but IIRC newer models shows how it has preferentially settled “out of… Read more »
Torbjorn Larsson OM
Member
Torbjorn Larsson OM
August 15, 2010 8:12 AM

deficit in old (pop I ?) stars by a factor 2 or so, but IIRC newer models shows

Yes, no, yes, no. Deficit, pop 2, a factor ~ 3, and Salacious paper (thanks!) shows that the debate is ongoing. I must have read one specific paper at some time.

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