hckrnws
Cecilia Payne-Gaposchkin discovered that stars are mostly made of hydrogen
by _Microft
Two other women who have made similar profound impacts upon astronomy are Henrietta Swan Leavit (who discovered Cephid Variable stars, which are used as "standard candles" for distance measurement), and Jocelyn Bell (who discovered the pulsar class of neutron stars).
The theory that hydrogen fusion powers stars is actually older than the discovery that the sun is made of (mostly) hydrogen. Eddington proposed it in 1920. It wasn't necessary to assume a "mostly hydrogen" sun—his estimate was that a >5% hydrogen sun would be sufficient.
https://sci-hub.se/10.1126/science.52.1341.233
The immediate historical motivation wasn't the discovery of hydrogen in the solar atmosphere, but the discovery, on Earth, that the hydrogen atom is anomalously heavy (~1% mass excess per nucleon).
(Eddington's is rather an astonishing paper, science aside, just for the remarkable breadth of perspective written down in one place 100 years ago. Within eight pages, he is contemplating all of:
- The perspective that all of the matter life is made of may have been forged in the "crucibles" of stars;
- The perspective that the timeline of the planet Earth should be expanded from ~20 million years, to multiple billions (and the specific implications for biological evolution);
- The perspective that hydrogen fusion could be the energy source of future civilization—or a source of weapons that end it
All of this, purely speculative theorizing, in 1920!
I think the point about the age of the earth and evolution might be backwards.
Lord Kelvin had worked out that the earth might be only 20 million years old maybe 60 years earlier based on continually losing heat.
But even at that earlier time biologists and geologists were suggesting that number wasn't high enough to explain what they were seeing in their fields. I think Darwin had suggested a lower bound of at least 300 million based on the erosion he saw locally.
> All of this, purely speculative theorizing, in 1920!
What speculative theorizing are we doing in the 2020s that we might similarly look back upon?
All that superstring and supersymmetry stuff.
Maybe Dark Matter and Dark Energy?
Inflationary cosmology.
Extraterrestrial intelligence/life.
I went down an interesting rabbit hole recently, I was trying to figure how big the iron core of the sun was and the answers were surprisingly all over the place.
There is the no iron core/fractional percentage gang which bases their theory on the observed sun, but this conflicts with the common cloud theory of solar system origin, which is basically there was enough iron in the proto cloud to provide iron cores for most of the inner planets and you are telling that you think that most of this iron did not end up in the middle of the sun.
then at the far end of the spectrum is the crackpot "the solar system is a second generation(minimum) system, some star must have exploded to form the metals we see, the core of the sun is probably the stellar remnant of the first generation system and is mostly iron"
But really I wonder, all our observations of the sun are of the upper atmosphere, and more importantly the light emitted by the upper atmosphere, if earth was observed the same way you would conclude it was mainly made of nitrogen.
I recently realized it takes light over 4 seconds to cross the diameter of the sun. It seems absurd to conclude what's inside it based on light emitted at the surface. Other methods of deduction maybe, but not that.
The Sun is opaque to light in its interior. The light we see -and its absorption lines- is emitted in the photosphere, far from the core.
Our sun does not have an iron core. If it did, it would immediately collapse into a black hole.
When the sun burns all of the hydrogen in the core, it will then burn helium. The burning will end at carbon.
https://en.m.wikipedia.org/wiki/Carbon-burning_process
Silicon burns to iron, which becomes degenerate matter that cannot resist gravitational collapse.
> Our sun does not have an iron core. If it did, it would immediately collapse into a black hole.
Even if the sun were 100% iron, at its current mass it would not collapse into a black hole.
chasil is talking about a star that was able to form an iron core naturally through fusion, not a thought experiment of a ball of iron with the same mass as the current Sun.
This hypothetical is getting into "if my granny had wheels she'd be a wagon" territory.
I interpreted the original comment as if the Sun, with its current mass, had an iron core. A star with the mass of the Sun cannot have produced iron, so it would have had to have formed with an iron core. This is certainly ruled out by other data, of course.
Linking to Wikipedia is ridiculous here, considering we are discussing the current scientific debate and consensus. You just worded your contribution more forcibly.
There was a bunch of iron in the proto dust cloud that formed this solar system(i pick on iron because it is a nice infliction point past which you get no energy from fusion, but really include all of the middle stable elements here), as the dust cloud collapsed it formed an iron core in all the planets, and many asteroids. but no core in the sun, explain how that is possible.
really, I expect at minimum an earth sized iron core in the sun, it is probably much more.
The Earth has an iron core because iron separated into a separate chemical phase that was denser, and this denser phase percolated downward into the center.
The Earth does not have its iron core because individual iron atoms, being heavier, individually diffused downward into the core. Some heavy elements, like uranium, are actually highly concentrated in the continental crust, because chemically they partition into lower density phases.
In the Sun, with everything inside vaporized, there is and was no partitioning into distinct chemical phases of differing density. There is a chemical difference in the Sun's core, though: it is now enriched in helium and somewhat depleted in hydrogen because of nuclear fusion over billions of years. This process is gradually making the core denser and hotter, increasing the overall rate of fusion. The Sun is now 30% brighter than it was when it settled onto the main sequence.
Separation by mass of ions does occur in the surface layers of white dwarf stars; the conditions there are such that separation by diffusion can be significant. Some such stars have been seen with "metals" (elements heavier than helium) in their crusts; this has been interpreted as evidence of recent accretion of material from disrupted asteroids or planets.
What fraction of crustal uranium would you estimate was sourced from the "late veneer"?
Very little? The ratio of uranium to platinum in the crust is many orders of magnitude higher than in carbonaceous chondrites.
The sun's core is overwhelmingly composed of helium and hydrogen, with about 1% oxygen and about %1 everything else. At least according to the standard model, I don't know how much "wiggle room" there is in our understanding
https://en.wikipedia.org/wiki/Solar_core
At the edge of the core is about 70% hydrogen 28% helium with the helium fraction increasing up to 66% right at the center.
One thing I think you're missing is how overwhelmingly the cloud that formed the solar system was hydrogen and helium.
https://en.wikipedia.org/wiki/Formation_and_evolution_of_the...
The gas cloud that formed the solar system is expected to have been 98% hydrogen and helium, 2% everything else. We don't see these ratios on rocky planets like earth because the gravity here isn't strong enough to hold the hydrogen and helium, so mostly it escaped and we have a wildly non-representative sample of elements left.
There is enough iron in the Sun for an iron core.
Nevertheless, the standard model of the Sun supposes that, because of the very high temperature, the interior of the Sun remains mixed well enough so that the heavy elements like iron cannot segregate to form a distinct core, but only, as you have mentioned for helium, the concentration of heavy elements is somewhat higher in the center than at the surface.
However the standard model of the Sun is not very certain, because the behavior of matter at extremely high pressures and temperatures is not known well enough.
The Sun has iron in it. There are at least 500 earth-masses worth of iron in the Sun. But it's distributed all throughout the Sun and not collected into the core. Do you have a PhD in solar plasma computational fluid dynamics modeling? No?? Then maybe pay attention to what mainstream astrophysics people say about the Sun's core.
Please leave credentialism out of it.
IANAA
If there was an iron core, it would vaporize in the center of the sun because it's extremely hot there.
A few years ago, someone measured the energy of the neutrinos produced by the fusion in the center of the Sun [1].
[1] perhaps there are some details in https://en.wikipedia.org/wiki/Solar_neutrino
An iron core is actually the precursor for either a black hole or a neutron star.
There is an exothermic fusion chain of elements that are burned in stars, the last stage of which is silicon, that ends with iron.
https://en.m.wikipedia.org/wiki/Silicon-burning_process
At iron, no further exothermic fusion is possible, so the core is no longer able to resist the pressure of collapse.
The iron atomic nuclei themselves break down, the protons combine with electrons to form neutrons where they are able, and if the total mass is below the Tolman–Oppenheimer–Volkoff, then neutron degeneracy pressure is able to stop the collapse, otherwise a black hole forms.
https://en.m.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E...
A star needs to be 8 solar masses for this to happen. Our sun ends at carbon.
But it the star is't a gas core made of Iron mixed with Hydrogen, Helium and other intermediate stuff, or it's a solid metallic almost pure Iron like on Earth? (IANAG neither)
For a sufficiently massive star, all of the hydrogen, helium, carbon, neon, oxygen, and silicon in the core are gone after silicon burning is complete.
They were consumed as fuel to maintain the outward pressure of the core.
> A star needs to be 8 solar masses for this to happen. Our sun ends at carbon.
Wikipedia says the TOV limit is ~3 solar masses?
I know, that this doesn't help really, but in plasma physics as well as when dealing with degenerate matter and such 8 and 3 are the same number. Most of the time a scientist in these fields is happy to get the order of magnitude right! ;P
"Assume Pi is 1" is such a great conversation starter!
A new play based on her life has just opened in London: https://www.hampsteadtheatre.com/whats-on/2024/the-lightest-...
There is also a substantial article on Wikipedia about her if you want to know more:
I loved this bit:
“In her autobiography, Payne tells that while in school she created an experiment on the efficacy of prayer by dividing her exams in two groups, praying for success only on one, the other one being a control group. She achieved the higher marks in the latter group.”
Assuming the result was statistically significant, what would be the theory she used to explain the result? Evidently god does not exist (it says she became an agnostic in later life). But in that case wouldn’t the two groups have similar outcomes? Probably the thought of an outside force helping vs I’m on my own thinking was the cause. Or God had other plans for Cecilia.
> Assuming the result was statistically significant, what would be the theory she used to explain the result?
Assuming the result was statistically significant:
It's very difficult to isolate all the variables. Perhaps the last 15 minutes before the exam she prayed instead of studding. Perhaps she studied less because she secretly hoped the experiment to go this way.
Double blind randomized controlled trial or it didn't happen.
Also, there is reporting bias, for example if she got the oposite result, perhaps she would have not mentioned it so often.
And perhaps she has some methodological error we can guess without a detailed report. Perhaps she had some weird exception list in the exams she counted.
Preregistered double blind randomized controlled trial published is a serious peer review journal or it didn't happen.
And we now have to discuss what serious means that is another can of worms. And ignore the webpages that claims that the comment section is peer review.
Too late to edit: I forgot a random fluke https://xkcd.com/882/
One simple theory is that God does not like to be tested. That's also plainly said in the Bible.
Seems odd that she would test the efficacy of someone else intervening without first confirming if they'll participate.
Finding proof that prayer works would violate free will (specifically the free will to choose to believe or not believe), and since free will is the most fundamental of all of God's rules, there is no chance at all for this kind of study to ever find a result.
If you need elaboration: For God to impose a punishment or give a reward the person must have free will. If you took that away, then humans would become like animals (or angels if you prefer) who don't have free will. When Genesis 1:27 says "in his own image", that's what it means: With free will.
This also means there's essentially a religious mandate to study science. Science is God's alternative explanation for how the world works, so studying it is essentially studying God.
This is also why Young Earth Creationists don't understand their own religion. They are attempting to find proof of God, which is something that their own religion claims isn't possible.
All of this just strikes me as a lot of elaboration on fundamentally silly ideas. When I was young and fresh out of the religion I was raised in, I felt this powerful need to like logically debunk it. But now that I'm older I feel dumb for ever feeling the need to do that. Literally the only thing Christianity has going for it as a serious hypothesis about the world is word of mouth. "A lot of people believe this" isn't a good reason to believe something since a lot of people also clearly believe in Islam, Buddhism, etc, etc, which are mutually exclusive.
I guess I say this because I wish someone had told younger me: "You just don't need to believe any of this stuff. You don't need an argument for doing so, really, just like you never needed an argument not to be Jain or Hindu. You can just stop believing it."
In any case, I don't buy this particular argument anyway. In fact, one can just as easily construct the exact opposite: a person's will isn't free unless they have perfect information. God had to reveal himself directly in the inspired works of the bible because if people didn't know that he existed it would be unjust to judge them for deciding or failing to decide to follow him.
Angels, in fact, according to some adherents of your religion, knew everything about the reality of God and some still chose to disobey and were punished. And we don't exactly have to comb the new Testament to find examples of Jesus working miracles/granting prayers right in front of everyone, which also contradicts your idea.
Christian apologetics is a big pile of bad arguments.
I really like how people write this is a sort of a feature of Christianity when in fact a bunch of people sat down and invented excuses to explain stuff exactly like they do in sci-fi books.
Everything you just said is a hypothetical. So is the existence of the Rabbit's hole in Alice in Wonderland.
> God's rules
Who? What are these rules of which you speak? Which respectable peer-reviewed publication may I find the rules in?
I know this is somewhat tongue in cheek, but I'm going to answer as if it's serious:
Did she randomly decide which ones she would pray for? Perhaps she was more likely to pray when she knew she was less prepared.
> what would be the theory she used to explain the result
If god does exist, then this is not a double blind experiment.
The result of that experiment could mean a variety of things, such as:
- sample size too small (too few tests,
too few test subjects)
- poor test setup
- praying for success made her complacent,
thus not leading to success as often as
when not praying for success
- praying for oneself is not rewarded but
punished
- God does not permit scientific experiments
to prove God's existence, even indirectly
via measuring the effectiveness of prayer
- other reasons such as your "[o]r God had
other plans for Cecilia".
Anyways, that test does not pass the smell test for me.
If prayer was effective, wouldn't industry and governments capitalize on it? I'd expect to see a prayer department in any major corporation or government.
I guess one group had more time to study
Thanks, I didn't know about her which is a shame because her discovery is Nobel worthy..
She has a patera (volcanic crater) on Venus named after her https://planetarynames.wr.usgs.gov/Feature/4623
compare https://xkcd.com/2340/
It's really funny because my dad (a chemical engineer) had a hobby interest in cosmology. He used to go nuts about people calling produce "organic" and would love to point out that all produce is organic in the sense that it all is made of carbon-based molecules. Yet on the other had no problem with the fact that cosmologists call just about everything in the whole periodic table a metal.
...unless they are (massive enough to be) at the other end, the "silicon burning phase."
Don't blink.
The page says very brief. The source cited states 18 days for a 15 solar-mass star.
[dead]
Record levels of solar-related deaths this year spawned calls for increased research of the sun to identify potential solutions, with some groups calling for sun-related regulation to reduce the shockingly high death tolls, including those related to heatstroke and famine, as well as longer-term issues including skin-cancer. Hurricanes are also considered a major issue given their proximity to the Capitol.
Also at issue is the large amount of the chemical element hydrogen which makes up the sun, which is a significant fire hazard, though some in the scientific community downplay its risk.
The issue is expected to be especially significant in this election year.
Left-wing politicians in Congress are calling for more sun research funding to provide greater clarity on the issues facing voters, though several of their more extreme members have already introduced competing bills to the House floor with proposals to reduce solar intensity, increase shielding around at-risk neighborhoods, or mandate warning labels in key locations.
Conservatives members of Congress deny that the sun is a significant source of risk, or in the event that it is an issue, that Congress should enact legislation to address the problem. "US citizens are aware of the risks, and should be able to exercise their god-given rights to do as they please in the sun."
On the far right end of the spectrum the senator from South Florida has introduced legislation to reclassify hydrogen as helium, an inert gas that poses no burn risk, and has industrial and commercial uses that would be a boon to US industry.
The senator was quoted as saying, "We've got to prevent foreign helium from undercutting the US market, and so my bill would radically increase the supply of this critical element used in birthday balloons while protecting US jobs from unfair competition." The senator had no comment about reports of contributions to his campaign from the American Society for the Suppression of Helium, Oxygen, and Lithium in Energy imports.
/s
Crafted by Rajat
Source Code