The reason why they're called planetary nebulas is that they have a similarity with the (back then newly discovered planet) uranus/neptune (can't remember which one). They are small, bright and often round(-ish). Also: Great video! Love this series!
Thanks for the info! The first astronomy course I ever took, the professor off-handedly said something like, "they're called like that cuz they look like planets... since both are round." I always thought he was being facetious, essentially saying the name makes no sense. But I guess it's actually true!
At last ! Refreshing explenation. some others are good too, but this one just adds to the hole. please excise my english ! thanks good presentation. it was up to my expectative.
Mass is not conserved in nuclear reactions. Energy is. The total mass of the nucleus is lower than the sum of the free nucleon masses. The lost mass is carried away by the emitted particles via E = mc^2.
The time back in the early eighties when the sun glowed blood orange and people panicked and thought it was a sign of the end times is the reason this this video might have been made
I covered nuclear reactions, stability, and the more common processes found in stars in much greater detail in chapter 5 of this series: th-cam.com/play/PLpkegBCPWkWMkWKHajtpGRK11kCnNiKro.html&si=H_d6KQy8dRN-stKI Having said that, I explain how it works more qualitatively. If you really want full mathematical derivations, that requires an advanced understanding of thermo, quantum, E&M, and particle physics. Beyond the scope of this series. You can check out a book called "Principles of Stellar Evolution and Nucleosynthesis" by Donald Clayton
Am i correct in thinking that after the core runs out of hydrogen in high mass stars, there are phases where the star expands into a red giant followed by a phase of contraction?
All stars will turn to red giants after hydrogen runs out (with a few possible exceptions). High mass stats will burn all the way to iron. Even though the red giants look bigger, this is only because the envelope expands, and that’s what we see (where light leaves the star). But the core and the bulk of the mass contracts with each subsequent nuclear burning phase.
You were careful to note that a positron must be emitted when two protons and one changes into a neutron. But then the positron just annihilates with an electron… so doesn’t that still leave the star with a net positive charge?
Initially there are equal numbers of protons and electrons. A proton converts to a neutron, emitting a positron. The positron then annihilates with an electron. The net effect is: loss of a proton (positive) + loss of an electron (negative) + gain of a neutron (neutral). Net charge remains 0 as equal amounts of positive and negative charge has been lost/gained. Hope this clears things up.
Good question. Keep in mind the onion diagram is a gross oversimplification. It only shows the most common nucleus. But in fact there are all sorts of nuclei being produced. Really this layer has a Ne-O-Mg mix. Ne is just most abundant. After carbon is made the various combinations for making heavier nuclei gets pretty complex. But it turns out the most likely interaction for carbon fusion is C + C -> Ne + He. The next most likely interaction makes Na which then combines with a proton to make more Ne. Oxygen can also be made via carbon burning, but it’s more likely to be made via neon burning. The next fusion stage.
@claudianreyn4529 that’s right. If you want a better idea you can check out this video that gives a more detailed (but still simplified) overview of later nuclear burning stages. th-cam.com/video/A08lz7ufkvU/w-d-xo.htmlsi=ZymSAk-C67vWL5z_
In the first step of the proton-proton-chain reaction , where 2 protons collide , Deuterium is formed because 1 of the protons is turned into a neutron thru beta + decay. Does this beta decay always happen ? If so , how does one proton know when to turn into a neutron ? Why don't they both turn into a neutron ?
Excellent question. Beta decay is probabilistic. So it doesn’t happen every time. In fact most of the time it doesn’t happen. As a result both protons decaying at the same time is very unlikely. Anyway two bound neutrons is energetically unstable, so in the off chance it does happen they break up almost immediately.
You say the nuclear force is not strong enough to bind 2 free neutrons. Then how can a neutron star be stable? Is that purely due to gravity ? Thankx for answering my question and thankx for your excellent videos.
@@pellythirteen5654 I wouldn't say the nuclear force is not strong enough to bind two neutrons together. A better way of saying it is that two free neutrons have less energy than two bound neutrons. Nature "wants" to minimize energy, so the bound state is (highly) unstable. free neutrons are also unstable it turns out. They will decay to protons and electrons. To understand what determines stability and binding energy of a nucleus you can watch my two videos on the topic: binding energy: th-cam.com/video/CgA7IocT4N4/w-d-xo.htmlsi=hAXLLC7UNR9kMKlP Nuclear stability: th-cam.com/video/mJlGRveBXYg/w-d-xo.htmlsi=IVQsYghm2D8Nouvh They are a little more technical than this video, but essentially its whatever state has lower energy is more stable. The reason a neutron star is stable, is in short, as you said: gravity is so strong that it holds it together. It is a little more complicated than that as neutron stars are made of degenerate neutrons, so the thermodynamics of that kind of material is rather strange, and this contributes as well. Ultimately the answer is the same: given the particular configuration (gravity, degenerate matter, etc.) it is more energetically favorable (lower energy) to have a bunch of neutrons, rather than neutrons, protons, and electrons. I have a few videos in this series on degenerate matter and neutron stars as well if you're interested.
Thanks for your elaborate answer. I was mainly interested whether the strong force could build a neutron star and the answer is NO ! I think I have watched all of your vidoes but will go over them again. Degenerate matter (electrons/neutrons) is still something I'm having trouble to understand , but I think of it as : The Pauli-exclusion principle no longer holds. P.S I have written a Delphi-program to calculate the semi-empirical mass and having fun doing reaction energies. Next step is to calculate cross-sections and have a toy "reactor".
@@pellythirteen5654 "The Pauli-exclusion principle no longer holds" It's the exact opposite! Degenerate matter is matter pushed to the point where the physics is entirely dominated by the Pauli exclusion principle. The particles, say electrons, are crunched together so tightly that an enormous pressure results from the Pauli exclusion principle preventing further contraction. This is degeneracy pressure. For neutron stars, they are so compact that in order to overcome this pressure, it becomes energetically favorable (less energy) to convert electrons and protons into neutrons (normally an electron + proton has less energy than a neutron). This allows the star to crunch down further until the degenerate limit is reached for neutrons, and the neutron degeneracy pressure balances out gravitational collapse.
I don't recall the exact history, but I think you're basically right. Experiments involving beta decay found energy, momentum, and angular momentum weren't conserved. So it was posited (by Pauli I think) that a small neutrally charged particle was also being emitted to conserve all three (yes neutrinos have momentum and angular momentum as well).
Technically fusion can occur past iron 56 and still produce energy, however, the nuclei produced get less tightly bound and the Coulomb barrier will become much stronger and almost impossible to overcome.
Yes, fusion definitely takes place after iron (otherwise we wouldn't have most of the periodic table). And yes due to the binding energy vs atomic number curve being bumpy, technically there are processes that release energy, but on net all have more energy than iron. So energy is absorbed rather than released beyond iron. This means that despite plenty of fusion beyond iron taking place inside stars (the coulomb barriers are much higher, but they're not difficult to overcome given the extreme temperatures in a collapsing core), there is no longer an energy source to provided pressure support against gravity, and the star collapses before exploding in a supernova. Beyond iron nuclei created during the collapse don't matter as they are destroyed (and then recreated) during the supernova. I covered this and the other nuclear burning stages in detail in chapter 5 of this series if you're interested.
@Hydrolysisisfun I’m not sure I understand what you’re saying. What produces energy? The energy in stars is created via fusion. If there is no fusion there is no energy produced. And nuclei heavier than iron have more energy per baryon than iron, so they have absorbed energy after iron, rather than produced it.
@@physicsalmanac Well I think it depends on what you are fusing with iron, lighter elements like hydrogen , helium, and lithium, can combine exothermically with iron, but these elements rarely coexist in the core of stars because by the time significant iron is produced, all of the helium and hydrogen in the core have been burned up.
@@Auroral_Anomaly Oh I see what you're saying. When I say iron, it's really a shorthand for iron peak nuclei. At the onset of collapse most of it is iron any way. This video is just a basic overview of the nuclear burning stages. I go into greater detail in chapter 5.
That’s right! You can check out my video on helium fusion/triple alpha, and I talk all about his contributions th-cam.com/video/bV-YZ441z4Q/w-d-xo.htmlsi=DABDl-P5eIQCL0SW
@@gr8points17 It really just depends on what your theory/paper is about exactly. Different journals are geared towards different fields. Here's a list of physics journals by subfield: en.wikipedia.org/wiki/List_of_physics_journals
It's crazy how the heat and cold are important for the protons to continue being active and grow like a tree growing bearing different proton fruit in hot weather summer but also live through the cold nights too in the winter. Like a hot magnet that hovers in cold ice. I was always training in hot conditions but also ice myself training in the winter cold outside to where I had way too much energy dunking before high-school running the fastest and had a stiff cocktail all the time. I want to add magnets on me to suppress my training days
![The Insane Science of Neutron Stars [4K]](http://i.ytimg.com/vi/qX6h72IyKSo/mqdefault.jpg)
the best fusion explanation I have ever encountered, bravo 👏
The reason why they're called planetary nebulas is that they have a similarity with the (back then newly discovered planet) uranus/neptune (can't remember which one). They are small, bright and often round(-ish). Also: Great video! Love this series!
Thanks for the info! The first astronomy course I ever took, the professor off-handedly said something like, "they're called like that cuz they look like planets... since both are round." I always thought he was being facetious, essentially saying the name makes no sense. But I guess it's actually true!
At 3:05 atomic number only relates to number of protons. So the ²H still has an atomic number 1, but does have a nucleon number of 2.
Oh you’re right. I meant A = mass number.
2:20 : the neutrino is necessary to conserve spin
At last ! Refreshing explenation. some others are good too, but this one just adds to the hole. please excise my english ! thanks good presentation. it was up to my expectative.
At 2:24
Since Neutrons are heavier than protons, how is mass conserved in this first fusion event?
Mass is not conserved in nuclear reactions. Energy is. The total mass of the nucleus is lower than the sum of the free nucleon masses. The lost mass is carried away by the emitted particles via E = mc^2.
The time back in the early eighties when the sun glowed blood orange and people panicked and thought it was a sign of the end times is the reason this this video might have been made
That’s definitely why I made it ;)
1:45 : two hydrogen nuclei, not helium
Could you please share some resources where we can learn the math also? Thank you very much!
I covered nuclear reactions, stability, and the more common processes found in stars in much greater detail in chapter 5 of this series:
th-cam.com/play/PLpkegBCPWkWMkWKHajtpGRK11kCnNiKro.html&si=H_d6KQy8dRN-stKI
Having said that, I explain how it works more qualitatively. If you really want full mathematical derivations, that requires an advanced understanding of thermo, quantum, E&M, and particle physics. Beyond the scope of this series. You can check out a book called "Principles of Stellar Evolution and Nucleosynthesis" by Donald Clayton
Am i correct in thinking that after the core runs out of hydrogen in high mass stars, there are phases where the star expands into a red giant followed by a phase of contraction?
All stars will turn to red giants after hydrogen runs out (with a few possible exceptions). High mass stats will burn all the way to iron. Even though the red giants look bigger, this is only because the envelope expands, and that’s what we see (where light leaves the star). But the core and the bulk of the mass contracts with each subsequent nuclear burning phase.
You were careful to note that a positron must be emitted when two protons and one changes into a neutron. But then the positron just annihilates with an electron… so doesn’t that still leave the star with a net positive charge?
Initially there are equal numbers of protons and electrons. A proton converts to a neutron, emitting a positron. The positron then annihilates with an electron. The net effect is: loss of a proton (positive) + loss of an electron (negative) + gain of a neutron (neutral). Net charge remains 0 as equal amounts of positive and negative charge has been lost/gained. Hope this clears things up.
Why is the Neon layer on top of the Oxygen layer? Neon is heavier than Oxygen.
Good question. Keep in mind the onion diagram is a gross oversimplification. It only shows the most common nucleus. But in fact there are all sorts of nuclei being produced. Really this layer has a Ne-O-Mg mix. Ne is just most abundant. After carbon is made the various combinations for making heavier nuclei gets pretty complex. But it turns out the most likely interaction for carbon fusion is C + C -> Ne + He. The next most likely interaction makes Na which then combines with a proton to make more Ne. Oxygen can also be made via carbon burning, but it’s more likely to be made via neon burning. The next fusion stage.
@@physicsalmanac Thanks for the answer, yes, I guess there are a lot of fusion stages until Fe.
@claudianreyn4529 that’s right. If you want a better idea you can check out this video that gives a more detailed (but still simplified) overview of later nuclear burning stages.
th-cam.com/video/A08lz7ufkvU/w-d-xo.htmlsi=ZymSAk-C67vWL5z_
In the first step of the proton-proton-chain reaction , where 2 protons collide , Deuterium is formed because 1 of the protons is turned into a neutron thru beta + decay.
Does this beta decay always happen ? If so , how does one proton know when to turn into a neutron ? Why don't they both turn into a neutron ?
Excellent question. Beta decay is probabilistic. So it doesn’t happen every time. In fact most of the time it doesn’t happen. As a result both protons decaying at the same time is very unlikely. Anyway two bound neutrons is energetically unstable, so in the off chance it does happen they break up almost immediately.
You say the nuclear force is not strong enough to bind 2 free neutrons. Then how can a neutron star be stable? Is that purely due to gravity ?
Thankx for answering my question and thankx for your excellent videos.
@@pellythirteen5654 I wouldn't say the nuclear force is not strong enough to bind two neutrons together. A better way of saying it is that two free neutrons have less energy than two bound neutrons. Nature "wants" to minimize energy, so the bound state is (highly) unstable. free neutrons are also unstable it turns out. They will decay to protons and electrons. To understand what determines stability and binding energy of a nucleus you can watch my two videos on the topic:
binding energy: th-cam.com/video/CgA7IocT4N4/w-d-xo.htmlsi=hAXLLC7UNR9kMKlP
Nuclear stability: th-cam.com/video/mJlGRveBXYg/w-d-xo.htmlsi=IVQsYghm2D8Nouvh
They are a little more technical than this video, but essentially its whatever state has lower energy is more stable.
The reason a neutron star is stable, is in short, as you said: gravity is so strong that it holds it together. It is a little more complicated than that as neutron stars are made of degenerate neutrons, so the thermodynamics of that kind of material is rather strange, and this contributes as well. Ultimately the answer is the same: given the particular configuration (gravity, degenerate matter, etc.) it is more energetically favorable (lower energy) to have a bunch of neutrons, rather than neutrons, protons, and electrons. I have a few videos in this series on degenerate matter and neutron stars as well if you're interested.
Thanks for your elaborate answer.
I was mainly interested whether the strong force could build a neutron star and the answer is NO !
I think I have watched all of your vidoes but will go over them again.
Degenerate matter (electrons/neutrons) is still something I'm having trouble to understand , but I think of it as : The Pauli-exclusion principle no longer holds.
P.S I have written a Delphi-program to calculate the semi-empirical mass and having fun doing reaction energies. Next step is to calculate cross-sections and have a toy "reactor".
@@pellythirteen5654 "The Pauli-exclusion principle no longer holds" It's the exact opposite! Degenerate matter is matter pushed to the point where the physics is entirely dominated by the Pauli exclusion principle. The particles, say electrons, are crunched together so tightly that an enormous pressure results from the Pauli exclusion principle preventing further contraction. This is degeneracy pressure. For neutron stars, they are so compact that in order to overcome this pressure, it becomes energetically favorable (less energy) to convert electrons and protons into neutrons (normally an electron + proton has less energy than a neutron). This allows the star to crunch down further until the degenerate limit is reached for neutrons, and the neutron degeneracy pressure balances out gravitational collapse.
I assume neutrinos were first predicted to assure conservation of energy. Are neutrinos also involved in conservation of momentum?
I don't recall the exact history, but I think you're basically right. Experiments involving beta decay found energy, momentum, and angular momentum weren't conserved. So it was posited (by Pauli I think) that a small neutrally charged particle was also being emitted to conserve all three (yes neutrinos have momentum and angular momentum as well).
@@physicsalmanac the neutrino is now my favorite particle. The whole star freezer thing & "phasing through" matter.
@@Gunth0r You and every supernova expert! 😆 You're well on your way to being and astrophysicist.
Technically fusion can occur past iron 56 and still produce energy, however, the nuclei produced get less tightly bound and the Coulomb barrier will become much stronger and almost impossible to overcome.
Yes, fusion definitely takes place after iron (otherwise we wouldn't have most of the periodic table). And yes due to the binding energy vs atomic number curve being bumpy, technically there are processes that release energy, but on net all have more energy than iron. So energy is absorbed rather than released beyond iron. This means that despite plenty of fusion beyond iron taking place inside stars (the coulomb barriers are much higher, but they're not difficult to overcome given the extreme temperatures in a collapsing core), there is no longer an energy source to provided pressure support against gravity, and the star collapses before exploding in a supernova. Beyond iron nuclei created during the collapse don't matter as they are destroyed (and then recreated) during the supernova.
I covered this and the other nuclear burning stages in detail in chapter 5 of this series if you're interested.
@@physicsalmanac It produces energy, but not enough to initiate its own fusion and therefore stops.
@Hydrolysisisfun I’m not sure I understand what you’re saying. What produces energy? The energy in stars is created via fusion. If there is no fusion there is no energy produced. And nuclei heavier than iron have more energy per baryon than iron, so they have absorbed energy after iron, rather than produced it.
@@physicsalmanac Well I think it depends on what you are fusing with iron, lighter elements like hydrogen , helium, and lithium, can combine exothermically with iron, but these elements rarely coexist in the core of stars because by the time significant iron is produced, all of the helium and hydrogen in the core have been burned up.
@@Auroral_Anomaly Oh I see what you're saying. When I say iron, it's really a shorthand for iron peak nuclei. At the onset of collapse most of it is iron any way. This video is just a basic overview of the nuclear burning stages. I go into greater detail in chapter 5.
Fred hoyle worked in this area.
That’s right! You can check out my video on helium fusion/triple alpha, and I talk all about his contributions
th-cam.com/video/bV-YZ441z4Q/w-d-xo.htmlsi=DABDl-P5eIQCL0SW
Nice Video
Thanks! I'm glad you liked it.
@@physicsalmanac Welcome, I have created a theory so where can I publish it.
@@gr8points17 Submit it to some physics journals. Hopefully it will be accepted.
@@physicsalmanac Can you recommend some physics journals.
@@gr8points17 It really just depends on what your theory/paper is about exactly. Different journals are geared towards different fields. Here's a list of physics journals by subfield: en.wikipedia.org/wiki/List_of_physics_journals
why??????
hl physics was not the move guys
Martinez Timothy Thomas Steven Rodriguez Shirley
Now I'm really making fun of your superstitions
It's crazy how the heat and cold are important for the protons to continue being active and grow like a tree growing bearing different proton fruit in hot weather summer but also live through the cold nights too in the winter.
Like a hot magnet that hovers in cold ice. I was always training in hot conditions but also ice myself training in the winter cold outside to where I had way too much energy dunking before high-school running the fastest and had a stiff cocktail all the time.
I want to add magnets on me to suppress my training days