This is my favourite crash course series. Mainly due to Phil. I don't know, just the sheer amount of wonder and passion that he puts into this, makes appreciate this series on a whole other level than the others. Not to mention that he is talking about some of the most beautiful, powerful and eventful in... ever kinda helps.
I am not that interested in astronomy, but every time I see a CC:Astronomy pop-up in my subscription list I click it thinking "aw might as well". 3 minutes in I am staring at the screen going, "This is the most interesting thing I've ever heard of."
Phil hi, So I have a question that’s been bugging me for years. We’ve always been told that the gravity of a black hole is so strong that not even light can escape right? If that’s so, then how can material shoot out of the center of some these black holes? Does that mean that the matter shooting out is going faster than light? thanks for this series. Great stuff!!!!
+mcorrade The polar jets associated with some black holes aren't actually being shot out of the black hole. Rather, they are being shot out of the region just outside of the black hole (where matter can still escape). Matter tends to acrete around a black hole in a disk (called, somewhat uncreatively, an accretion disk). And as it sinks closer and closer to the hole's event horizon, continual collisions with other clumps of matter in the disk cause it to build up TREMENDOUS temperatures and pressures. Normally, that pressure would cause the material to expand back outward (even against the gravity of the black hole) but it is prevented from doing so by the rest of the accretion disk pushing in behind it. However, all that jostling can cause some of the matter to develop some up/down motion outside of the plane of the disk. Enough that when the material finally gets near the event horizon, it can have enough up/down velocity that it can "miss" the horizon and swing around it to the other side, like a spacecraft performing a flyby. If it happens to swing around in such a way that it ends up moving out of the plane of the accretion disk on the other side, then it suddenly finds itself free of the enormous pressure that was preventing it from expanding back outward. This, coupled with some very complicated magnetic effects due to the matter being fully ionized at the point, plus the gravitational acceleration imparted to it by its flyby of the black hole, gives it an enormous velocity (a significant fraction of the speed of light). And since it isn't actually inside the event horizon, that velocity is enough to allow it to escape the system along the poles of the accretion disk, producing polar jets.
if a white dwarf is comprised largely of carbon nuclei under immense pressure, shouldn't they be colossal sized diamonds? Or does the lack of electrons make that an impossibility?
+Pokemonlin99 No, neutron stars are different types of stars. They are held together by neutron degeneracy pressure not electron degeneracy pressure (like white dwarf). Neutron stars are end result of what happen when not too high mass goes supernova. I am sure they will cover this in their future episode.
Anyone else squeal like a little girl when you see there's a new CC:Astronomy video? I can't freaking wait to get to the black holes episode! You're one of my heroes Phil.
+Felipe josé I suspect next is novae then plausibly supernovae is the episode after. At some point beyond that we'll get into black holes, neutron stars and quasars I expect.
+Banana Hunter Pro Ours too! +1 to this excellent recommendation! Just to make it as easy as possible for anyone interested: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-vNaEBbFbvcY.html -Nicole
What happens to the orbit of a planet that gets swallowed? I imagine friction would slow it down and deteriorate the orbit. Do they fall into the center of the star or the star vaporizes it before that can happen?
A few years ago, I took an intro astronomy class taught by a respected astrophysicist in the community. She was incredibly smart, but I didn’t really learn much, and the class definitely wasn’t enjoyable. If I had been taught by Phil, it would’ve been my favorite class during my undergrad thus far. He’s so passionate and fascinated by this stuff, and rightly so, because it’s absolutely INSANE. Love this series. 10/10. It makes me want to take more astronomy courses.
Aw.. this is my third comments on this series. Would be really fun if ones can attend Phil Plait class. :D Love his way sharing knowledge so much! Thank you Phil Plait!
I love the way Phil presents this stuff. Not only does he make all the information easily digestible (with beautiful NASA photos), he also makes it relatable on our tiny, tiny level by talking about how these far-flung things in space have interacted with his own life in some way. Plus, I absolutely love all the silly faces, reactions, and truely awful jokes he puts in the episodes. Fantastic series!
That just blew my mind! The planets getting eaten by their star, BUT STILL ORBITING IT FROM INSIDE?! Like wtf?! That's the coolest thing ever!! Like how do you come up with that?! That's freaking incredible.
UUUhHHH, I learned something today. The idea for planets causing Planetary nebulae deformation is even new for me, and I am in the Astronomical community for 4 years. Although I am working with galaxies, soooo, ...
This crash course should be required learning in every school around the world. Phil makes it easy (somewhat) to digest and also fun to learn. Give this man a raise :)
Phil is absolutely my favourite crash course instructor. Trying really hard to get into the economics folks because I'd love to know more about how money works and how we think about it, but boy are they... noticeably new to being on camera.
So happy i found this. I loved astronomy when i was a kid but i watched Brian Coxs TV program on it and it destroyed my interest but now I've got it back thanks Phil
Several: 1) Mass of the dying star. White dwarfs are result of end of low mass stars. 2) Size. White dwarfs tend to about the size of planet Earth, while Neutron stars have a radius of about 20 km (and weight far in excess of white dwarf). 3) Nature of forming. White dwarfs are formed as a result of electron degeneracy, while neutron stars are formed as a result of neutron degeneracy. 4) Being smaller in size(but not weight!) neutron stars have a tremendous spin velocity. Hope this helps.
+Leo Staley Actually, it's everyone else who pronounces it strangely. When discussing metric units of distance, "kilometer" should be pronounced the same way as all the others distance units. Mi-lee-mee-ter, cen-tee-meet-er, kee-lo-meet-er. The "aw-met-er" pronunciation is used when one is referring to a device used to make measurements. Such as a bar-aw-met-er, a therm-aw-met-er, or a ray-dee-aw-met-er. So unless you are talking about a device used to measure a distance of a km, the correct pronunciation is kee-lo-meet-er, (not kil-aw-met-er).
Thank you very much for making this video, Phil Plait and the others at _CrashCourse_ Astronomy! I really enjoyed hearing about white dwarfs, planetary nebulæ and how they form. So beautiful! I hope you will mention black dwarfs sometime. ;D 10:14 Love that laughter! Love it!
Not only that, but white dwarfs are some of the most photometrically simple and stable objects in the universe. Their atmospheres are an almost perfect black body, with very few spectral features; and unlike main sequence stars (which have spots and flares, and yearly cycles) the amount of light put out by a white dwarf is stable on the
The gravity you feel depends on mass and your distance from the center of mass. A white dwarf has the same mass as the core of the star that formed it, but the white dwarf's surface is much closer to its center, so its surface gravity is higher. Imagine if you could travel straight through a star. As you approach the star's surface, the gravity you would feel pulling you toward the star's core would increase. However, once you reach the surface and start travelling inside it, some of the star's mass is behind you and is no longer pulling you toward the core. As you keep travelling, the force pulling you down would gradually drop to zero. If the star had the same mass, but was smaller (higher density like a white dwarf), you could get much closer to its center of mass before you reach its surface. Therefore the gravity you feel at its surface is stronger. If you really exaggerate the example and compress the mass down to a point, the "surface" IS the center of mass, so the gravity would keep increasing as you approached the center of mass, and would never decrease. This is why black holes are so interesting. Eventually, as that gravity increases, it reaches a point where nothing, including light, can escape.
Another question: If everything is simply, 'star stuff', as Carl Sagan claimed, how do you get the heavier elements, if by scientists own admission, the heaviest elements created in the belly of stars and the violence of novas and supernovas, where do the heavier elements come from? Is there some other celestial process that we have not covered that is pressing atoms together to create the heavier elements?
Man that's actually pretty sad... If we manage to survive millions of years until the sun burns us up, our only solace is that maybe some other alien life can at least see the system where *we* started at. But in the end, our star will end up just silently disappearing...
I still do not understand how stellar life cycles are presented as facts, when the time scales that stars go through are longer the the Earth itself? I agree with the measurements and everything about scale of what these things are, but their life cycles should come with a disclaimer that this is just theory. There is no way they have observed main sequence stars or Wolf Rayets going through any of these steps.
5:45 I accidentally did this to a black hole in Universe Sandbox 2. I made it explode, and it turned into many stars at just the right mass and density to become supernova, which caused a dozen jets to come off in a beautiful pattern. I didn't even mean to blow up my black hole... Clicked it by accident, but it was awesome. Totally unrealistic, but awesome.
Quick Question Phil: If light takes hundreds or thousands of years to reach us from this nebulae, are they already gone? If so, it brings up the possibility that all the farthest cosmic objects we have discovered in the last few decades, may not even physically exist today!
Just a question. A white dwarf is super compressed matter. Under such compression shouldn't the temperature remain hot forever? If a white dwarf has completely cooled down, will it be cold down to it's centre?
A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume is comparable to that of Earth. A white dwarf's faint luminosity comes from the emission of stored thermal energy; no fusion takes place in a white dwarf wherein mass is converted to energy.[1] The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun.[2] The unusual faintness of white dwarfs was first recognized in 1910.[3] The name white dwarf was coined by Willem Luyten in 1922. The universe has not existed long enough to experience a white dwarf releasing all of its energy as it will take many billions of years.[4] White dwarfs are thought to be the final evolutionary state of stars whose mass is not high enough to become a neutron star, which would include the Sun and over 97% of the other stars in the Milky Way.[5], §1. After the hydrogen-fusing period of a main-sequence star of low or medium mass ends, such a star will expand to a red giant during which it fuses helium to carbon and oxygen in its core by the triple-alpha process. If a red giant has insufficient mass to generate the core temperatures, around 1 billion K, required to fuse carbon, an inert mass of carbon and oxygen will build up at its center. After such a star sheds its outer layers and forms a planetary nebula, it will leave behind a core, which is the remnant white dwarf.[6] Usually, white dwarfs are composed of carbon and oxygen. If the mass of the progenitor is between 8 and 10.5 solar masses (M☉), the core temperature will be sufficient to fuse carbon but not neon, in which case an oxygen-neon-magnesium white dwarf may form.[7] Stars of very low mass will not be able to fuse helium, hence, a helium white dwarf[8][9] may form by mass loss in binary systems. The material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy. As a result, it cannot support itself by the heat generated by fusion against gravitational collapse, but is supported only by electron degeneracy pressure, causing it to be extremely dense. The physics of degeneracy yields a maximum mass for a non-rotating white dwarf, the Chandrasekhar limit-approximately 1.44 times of M☉-beyond which it cannot be supported by electron degeneracy pressure. A carbon-oxygen white dwarf that approaches this mass limit, typically by mass transfer from a companion star, may explode as a type Ia supernova via a process known as carbon detonation.[1][6] (SN 1006 is thought to be a famous example.) A white dwarf is very hot when it forms, but because it has no source of energy, it will gradually radiate its energy and cool. This means that its radiation, which initially has a high color temperature, will lessen and redden with time. Over a very long time, a white dwarf will cool and its material will begin to crystallize (starting with the core). The star's low temperature means it will no longer emit significant heat or light, and it will become a cold black dwarf.[6] Because the length of time it takes for a white dwarf to reach this state is calculated to be longer than the current age of the universe (approximately 13.8 billion years),[10] it is thought that no black dwarfs yet exist.[1][5] The oldest white dwarfs still radiate at temperatures of a few thousand kelvins.
A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, this type of star expels most of its outer material, creating a planetary nebula. Only the hot core of the star remains. This core becomes a very hot white dwarf, with a temperature exceeding 100,000 Kelvin. Unless it is accreting matter from a nearby star (see Cataclysmic Variables), the white dwarf cools down over the next billion years or so. Many nearby, young white dwarfs have been detected as sources of soft, or lower-energy, X-rays. Recently, soft X-ray and extreme ultraviolet observations have become a powerful tool in the study the composition and structure of the thin atmosphere of these stars. Evolution of a main sequence star An Artist's conception of the evolution of our Sun (left) through the red giant stage (center) and onto a white dwarf (right). A typical white dwarf is half as massive as the Sun, yet only slightly bigger than Earth. An Earth-sized white dwarf has a density of 1 x 109 kg/m3. Earth itself has an average density of only 5.4 x 103 kg/m3. That means a white dwarf is 200,000 times as dense. This makes white dwarfs one of the densest collections of matter, surpassed only by neutron stars. What's inside a white dwarf? Because a white dwarf is not able to create internal pressure (e.g. from the release of energy from fusion, because fusion has ceased), gravity compacts the matter inward until even the electrons that compose a white dwarf's atoms are smashed together. In normal circumstances, identical electrons (those with the same "spin") are not allowed to occupy the same energy level. Since there are only two ways an electron can spin, only two electrons can occupy a single energy level. This is what's known in physics as the Pauli Exclusion Principle. In a normal gas, this isn't a problem because there aren't enough electrons floating around to fill up all the energy levels completely. But in a white dwarf, the density is much higher, and all of the electrons are much closer together. This is referred to as a "degenerate" gas, meaning that all the energy levels in its atoms are filled up with electrons. For gravity to compress the white dwarf further, it must force electrons where they cannot go. Once a star is degenerate, gravity cannot compress it any more, because quantum mechanics dictates that there is no more available space to be taken up. So our white dwarf survives, not by internal fusion, but by quantum mechanical principles that prevent its complete collapse. Degenerate matter has other unusual properties. For example, the more massive a white dwarf is, the smaller it is. This is because the more mass a white dwarf has, the more its electrons must squeeze together to maintain enough outward pressure to support the extra mass. However, there is a limit on the amount of mass a white dwarf can have. Subrahmanyan Chandrasekhar discovered this limit to be 1.4 times the mass of the Sun. This is appropriately known as the "Chandrasekhar limit." With a surface gravity of 100,000 times that of Earth, the atmosphere of a white dwarf is very strange. The heavier atoms in its atmosphere sink, and the lighter ones remain at the surface. Some white dwarfs have almost pure hydrogen or helium atmospheres, the lightest of elements. Also, gravity pulls the atmosphere close around it in a very thin layer. If this occurred on Earth, the top of the atmosphere would be below the tops of skyscrapers. Scientists hypothesize that there is a crust 50 km thick below the atmosphere of many white dwarfs. At the bottom of this crust is a crystalline lattice of carbon and oxygen atoms. Since a diamond is just crystallized carbon, one might make the comparison between a cool carbon/oxygen white dwarf and a diamond.
7:20 Interesting how ideas are considered "nutty" by the scientific community until proven true, then they're obvious. Makes you wonder what other "nutty" ideas we hold now that might be obvious in the future.
06:45 , centrifugal force? Not centripetal force? I thought centrifugal force wasn't "real" but arises from moving frames of reference. Can someone please explain how it would be an applicable force here, or, why it's not centripetal force. Thanks!
I will ask again... you say that the core will become "almost pure carbon"... i suspect under tremendous pressure: will some part of it be like a diamond the size of... don't know... a small planet?
