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Current time:0:00Total duration:10:09

Video transcript

in the last video we saw that if we started with a massive star about 9 to 20 times the mass of the Sun and when it finally matures the remnant of the star is roughly or that remnant core of the star is roughly one and a half to three times the solar mass or the mass of the Sun then this remnant right here and let me just be clear this 9 to 20 times is the mass of That star when it's in its when it's in its main sequence this one and a half to three times is the mass once it's shed off a lot of the I guess outer material of the star and this is really the mass of the remnant of the star it kind of the core of the star but at that remnant once it stops using once it stops having outward pressure once it has enough density this we saw in the last video will cause a supernova little caused a shockwave to move out through the rest of the material and essentially caused it to blow up and this will condense this will condense into a neutron star into a neutron star now in this video what I want to talk about is what if we're starting with a star that has a mass more then this is give or take we don't know the actual firm boundaries here but what if we have a star what if we have a star that is more than 20 times the mass of the Sun and this is kind of the original mass before the star burns itself out or when when that star has kind of reached this old age once it has that iron core it has more than so I could say the remnant the remnant the dense remnant has more than three to four times the mass of the Sun and remember it's going to have more than three it's going to have three to four times the mass of some it's going to be far denser it's just going to be a core it's going to be an iron nickel core that's no longer fusing so what happens to these stars so it turns out that these are so massive that even even the neutron degeneracy pressure will not be enough to keep the mass from imploding and these stars all of the mass in these stars will just keep imploding so in the neutron so we imagine the first and kind of sun-like stars things would collapse into white dwarf so maybe I should draw that in white so they would collapse into white dwarfs now that's not white either there you go they would collapse into white dwarfs eventually so this is a white dwarf white dwarf and here the pressure that's keeping this from collapsing further is electron degeneracy pressure the atoms are squeezed so much that the electrons are essentially keeping them from squeezing anymore but if the pressure gets large enough then you have the neutron star so you have even more mass and even a smaller and I'm not drawing this to scale neutron stars are tiny white draw what white dwarf stars are on the scale of an earth-like planet neutron stars we learned in the last video are on the scale of a city so there's a super dense weird onion this has more mass than this over here tech maybe I'll actually just draw it as a dot just so you have a sense of how dense it is it's really just like one big atomic nucleus or well it's still small but the size of a city it's like a nucleus the size of a city but this right here is a neutron star neutron star and what's unintuitive about what I'm drawing is each of these smaller things have more mass this over came the electron degeneracy pressure to collapse even further but if the mass is large enough and this is what we're talking about in this video even the neutron degeneracy power will pressure will not be able to keep that mass from collapsing and there's even theoretical a quark stars where the cork degeneracy pressure but if you could even beyond that that all collapses into a into a single point and I'm simplifying here but it's simple APS's it to a single point of infinite density infinite mass density and this this is really the mass of a black hole and I'm calling it the mass of a black hole because there's different ways how you can view where a black hole starts and ends or what exactly is the black hole so this is all the mass all the mass of the black hole of the black or we could say of the original star so when we're talking about that remnant being 3 to 4 times 3 to 4 solar masses all of that mass is now being contained well not all of it some of it was released as energy during the supernova and that was also true of the neutron star but most of that mass is now being contained in this infinitely small point and you'll hear physicists and mathematicians talk about singularities singularities and singularities are really points and even in mathematics where everything breaks down where nothing starts to make sense anymore where the where the the mathematical equations don't give you a define answer and this is a singularity because you have you have a ton of mass in an infinitely small space you essentially have an infinite density right here and this is hard to visualize but you have kind of an infinite curvature in space-time right here and I can't visualize that so maybe we'll think about that in more videos but the reason why I said that it's it's there's different ways to think about where a black hole is or where it starts and ends is that this is where the mass is so and if there was any other mass that was over here would obviously be attracted to this mass and then become part of that singularity would add to that mass that that already huge mass it's in an infinitely small point in space but the reason why the boundaries hard to define is because there's some point at which there's some point in space around that singularity at which no matter what that thing is no matter how much energy that thing is it will not be able to escape the gravitational influence of the black hole of that ultra dense mass so even if it was even if it was electromagnetic radiation even if it was light and even if it's light that's that's shown away from the mass it will eventually have to go back it will not be able to escape the gravitational influence and so the boundary the boundary where if you're within that boundary that's really a sphere so that boundary around the singularity and that boundary around singularity where if you're within the boundary no matter what you do no matter if your electromagnetic radiation you're still going to you're never going to be able to escape the black hole if you are beyond that boundary you might be able to escape the black hole so this guy could escape this guy over here no matter what he does is going to have to go back into the black hole this boundary right here is called the event horizon this right here is the event horizon another word used in a lot of science fiction movies and for good reason because it's fascinating and we'll actually learn in the in future videos hopefully about Hawking radiation we'll see that that is not radiation from the black hole itself it's it's the byproduct of quantum effects that are occurring at the event horizon but the event horizon is just this it's it's this kind of point in space or the sphere in space or this boundary in space anything closer than or within the event horizon has to eventually end up in the singularity contributing to that mass anything on the outside has a chance of escaping so what would a black hole look like well not even light can escape from it so it will be black it will be black in in in the purest sense it will not emit any type of radiation from the black hole itself from with from that mass and so here are some here are some depictions I got from NASA of black holes and so just to be clear what's happening here what you're seeing here is black that is not you can view that as the black hole when people talk about the black hole that's often what they're talking about but there's there's a point of infinite density at the center of this of this black sphere right here and what you see is that black sphere that really is the boundary of the event horizon so this right here is the boundary of the event horizon and what we're seeing right here is the accretion disk around the black hole as as all of this matter gets closer and closer to it it's being squeezed more and more it's moving faster and faster and getting hotter and hotter and that's why the way this artist depict it looks like this stuff over here is redder and hotter than the stuff further out it's just accelerating as it approaches that event horizon once it approaches that once it's in the event horizon we cannot even see the light that is emitting even though it would be a you know starting to become unbelievably energetic here's some other pictures this is a this is a picture of a star being ripped apart not a picture this is actually artist's depiction all of these are artist depictions we never were able to get such good pictures of actual action occurring near black holes these are artist depiction but this is a star being ripped apart by a black hole so this the star is getting pretty close pretty close to this black hole already out here very you know where the star is it's very strong gravitational attraction so any mass any a that's being emitted from the star in that direction is slowly being pulled into the black hole so the star is kind of being ripped apart by the black hole this is maybe a better depiction of it this is the star at first and once it gets under once it becomes under the influence of of the black hole's gravitational on gate and gets ripped apart and it's matter goes start spiraling in closer and closer that black hole and then once it's in the event horizon we won't even see it anymore because even the light from that from that matter that intensely hot can matter that's entering into the black hole cannot even escape the black hole itself anyway hopefully you found that interesting and you know I want to be clear we still don't understand a lot about black holes in fact you know this whole notion of a singularity the fact that all the math and all the theory breaks down at the singularity is a pretty good sign that our theory isn't complete because if our theory is complete we would maybe get something a little bit more sensical than just all of our equations not making sense at that infinitely dense point anyway hopefully you found that interesting