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45 votes

Are we really star-stuff from the interior of collapsing stars?

The straightforward answer is, "Yes, we are made of star stuff." Some of it will be from the interior of collapsing stars, some will be from supernovas, some from normal everyday fusion, and some ...
Rory Alsop's user avatar
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44 votes
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Is lithium considered a metal in astronomy?

The latter. To astronomers, a metal is any element that is not hydrogen or helium, because these elements together constitute most of the elements in the Universe, by far. This means that, in many ...
pela's user avatar
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38 votes
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Why didn't the Big Bang produce heavier elements?

I think that your thought process is flawed in that you assume that by drastically increasing the temperature you are guaranteed to get heavy elements. As odd as this may sound, this isn't the case (...
zephyr's user avatar
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29 votes

Why don’t supergiants at least start to fuse nickel into even heavier elements before going supernova?

The final stages of nucleosynthesis are a statistical equilibrium process. At the same time as nuclei are being built up, photodisintegration is breaking them down. The temperatures required to ...
ProfRob's user avatar
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29 votes
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Formation of elements in the Sun other than helium

The Sun is currently turning hydrogen into helium. There are no other nuclear reactions taking place at any significant rate in the Sun. The Sun will not start to make heavier elements until it ...
ProfRob's user avatar
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27 votes

Do stars become more metal-rich as they evolve?

If the star is a solar mass or below it will not produce any metals (anything heavier than helium) within 10 billion years of birth. It will be on the main sequence, fusing hydrogen to helium via the ...
ProfRob's user avatar
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20 votes

Are we really star-stuff from the interior of collapsing stars?

Sagan's quote is half-correct. While some of these elements are created during or immediately prior to a supernova of some sort, others are either partially or entirely fused during normal stellar ...
HDE 226868's user avatar
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19 votes

Does a star fuse helium to beryllium on the main sequence?

Does a star fuse helium to beryllium on the main sequence? Stars don't fuse helium to beryllium except as a very, very short intermediate step toward carbon. Helium-helium fusion to form beryllium is ...
David Hammen's user avatar
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18 votes
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Is oxygen an alpha element?

Two things. The abundance of oxygen is a difficult thing to measure in optical spectra - much harder than Mg, Ca, and Si. So these latter are usually used to represent "the alpha elements". ...
ProfRob's user avatar
  • 153k
15 votes

What effects besides "mass defect" cause the alpha ladder beyond iron-56/nickel-56 to be endothermic?

There are plenty of misleading statements in Wikipedia and elsewhere on the internet about nucleosynthesis (I am busy searching to see if I have said something similar in the past!) The reason that ...
ProfRob's user avatar
  • 153k
15 votes

Do stars become more metal-rich as they evolve?

Yes, it will Metals in astronomy, are simply elements that are heavier than hydrogen and helium. From that perspective, even oxygen and carbon are "metals" in a astronomical sense, although ...
Alastor's user avatar
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14 votes
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Why do we want to normalize the solar abundance of elements to Si?

The abundances for many elements are judged or estimated from rocky material. i.e. Material that often contains silicon, but not that much hydrogen, or the hydrogen has been heavily modified. For ...
ProfRob's user avatar
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12 votes
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Why does lithium fuse at lower temperatures than hydrogen?

The slowest reaction rate in the pp chain determines how quickly hydrogen can "burn" in the core of a sun-like star. That rate-determining step is actually the fusion of two protons to form ...
ProfRob's user avatar
  • 153k
11 votes
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Does a star fuse helium to beryllium on the main sequence?

What defines the main sequence? Main sequence stars are characterized by hydrogen fusion in their cores, either through the proton-proton chain (for lower-mass stars) or the CNO cycle (for stars more ...
HDE 226868's user avatar
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9 votes
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Do we know how old the matter that makes us is?

The material (heavier than helium) that makes up the solar system was made in millions, if not hundreds of millions of stars that lived and died in the ~7 billion years between the formation of the ...
ProfRob's user avatar
  • 153k
9 votes
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Why do stars usually stop fusion at iron, even though nickel-62 has the highest binding energy per nucleon?

Contrary to common myth, the addition of alpha particles to iron-peak nuclei is exothermic. However, in the nickel/iron core of a massive star, there are no free alpha particles, they must be broken ...
ProfRob's user avatar
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8 votes
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Why is it that lithium and deuterium are burned before hydrogen?

Deuterium burns first because its combination with a proton or another deuteron is a pure strong nuclear force interaction, with the minimum of Coulomb repulsion. It occurs at lower temperatures than ...
ProfRob's user avatar
  • 153k
7 votes
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What is the length of time for each fusion process in a massive star?

My stellar astrophysics text, Francis LeBlanc's An Introduction to Stellar Astrophysics, gives the following quantities for the stages of burning in a $25M_{\odot}$ star (citing models by Arnould &...
HDE 226868's user avatar
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7 votes
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Does Oxygen-burning process produce Neon?

The pages you’re looking at describe fusion of two similar nuclei with each other (e.g. oxygen with oxygen). But fusion doesn’t have to involve identical nuclei, and reactions involving more abundant ...
Eric Jensen's user avatar
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7 votes

Why does iron consume more energy in the fusion process than it produces?

As can be seen in this question: What effects besides "mass defect" cause the alpha ladder beyond iron-56/nickel-56 to be endothermic? It is not so straightforward to explain why fusion ...
ProfRob's user avatar
  • 153k
7 votes
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Can I "see" nucleosynthesis in R Geminorum with a small telescope, a plastic diffraction grating and a cell phone? (famous technetium lines)

No, even if you could resolve the spectral lines, there is no way in your proposed experiment that you could distinguish the Technetium features from spectral lines due to many other chemical elements....
ProfRob's user avatar
  • 153k
5 votes
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"Turn on point" for fusion?

I don't have detailed model calculations to hand and I'm not sure they have been done for the small range of metallicity you mention. However, in handwaving terms. (1) Mass and composition are the ...
ProfRob's user avatar
  • 153k
5 votes
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Does Alpha Process Produce Bismuth?

Bismuth is produced via the s-process. It is the slow absorption of neutrons that can produce heavier elements beyond the peak of the binding energy per nucleon curve at iron. The alpha process isn't ...
ProfRob's user avatar
  • 153k
5 votes

Do the newly-created deuterons in our Sun release any photons? In addition to a positron and an electron neutrino?

Does the newly-formed deuteron then automatically release a photon? Not directly. The initial step of the p-p chain is a weak interaction rather than an electromagnetic interaction. This initial step ...
David Hammen's user avatar
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5 votes
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In layman's terms, why does the cold C-N-O process end in Carbon?

Both 15N($p,\alpha$)12C and 15N($p,\gamma$)16O can and do take place. However, the former is a strong force interaction, whilst the latter is mediated by the electromagnetic force and is known as a &...
ProfRob's user avatar
  • 153k
5 votes

In layman's terms, why does the cold C-N-O process end in Carbon?

This question has several misunderstandings. The CNO cycles (there is more than one CNO cycle) in a main sequence star have nothing to do with the triple alpha process. A star that is using the triple ...
David Hammen's user avatar
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4 votes
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Would dropping a white dwarf or a "still-hot" stellar core into a large planet or brown dwarf create a star?

The issue is not whether the dense core can fuse, but what fusion processes can occur on its surface. Remember that novas happen when gas accumulate on the surface of white dwarf stars: the high ...
Anders Sandberg's user avatar
3 votes

Formation of elements in the Sun other than helium

Pretty sure from my stellar nucleosynthesis days that the p-p I chain is the dominant form of nucleosynthesis in the sun, but the p-p II, p-p III, and p-p IV chains also occur, just to a much lesser ...
3 votes

What percentage of Helium-3 is primordial vs produced in stars

My question is 2-fold:   1. Is the primordial amounts of $^3$He significant or insignificant compared to what stars produce and eject by coronal mass ejections or blowing up into nebulas, ...
Rob's user avatar
  • 2,656
3 votes
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Can you recommend a book about big bang nucleosynthesis and chemical abundances?

I highly recommend Nucleosynthesis and Chemical Evolution of Galaxies by Bernard Pagel. It contains the basics of nuclear reactions andstellar evolution, chapters on big bang nucleosynthesis and light ...
ProfRob's user avatar
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