Humans can survive in this universe as long as we have an energy source. Unfortunately, the universe will die. It will happen slowly, over many billions of years, but it will happen. On a universal time scale, stars like our sun will be gone in no time. Luckily, there are places that will exist practically forever from a human perspective: the corpses of dead stars... white dwarfs. They could be humanity's last home right before the death of the universe. What are these strange things and what happens when they finally die? How long stars live varies drastically, depending on how massive they are. For example, really massive stars burn hot and fast, dying violently in supernovae a few million years after birth. But they're the exception. 97% of all stars will end their existence as white dwarfs. There are two ways this can happen: Small stars - so-called red dwarfs - burn out over trillions of years until they eventually quietly turn into white dwarfs. Medium-sized stars like our Sun are more interesting. Imagine the sun as a huge pressure cooker that fuses hydrogen into helium in its core through its gravity. The fusion of elements releases extreme amounts of energy, that pushes outwards and stabilizes the star, keeping it in a delicate balance. When the Sun is old, the hydrogen in the core is exhausted, and the Sun will begin to burn helium into heavier elements. While doing so, it will shed its outer layers. When this process is over more than half of the Sun's mass will be lost into space as a spectacular planetary nebula millions of kilometers across. What remains will be its former core: A white dwarf is born, a star corpse. While its former self was about 100 times its diameter, now it's only about as big as Earth, but still with about half of its former mass. This means it's extremely dense, a teaspoon of white dwarf is about as massive as a car. Its surface gravity is over 100,000 times higher than Earth's. If you tried to land on it, you'd immediately be compressed into a steaming puddle. Life around a white dwarf is very unlikely, but possible. Most of them that exist now were former stars that, well, died, which probably ruined any planets they once had. But that's not all: since they are so small, a planet would need to orbit them about 75 times closer than Earth is to the Sun to have liquid water. This proximity has up- and downsides: for one, it would tidally lock the planet giving it a permanent day and permanent night. At the edges of these day and night zones life could be possible. But white dwarfs have a very stable energy output, so they might actually be safer to live around than many red dwarfs. This is still speculation at this point, but if we could find the white dwarf with the right conditions to settle around, we could have a home for many billions of years. But why do they shine so much longer than other star types? White dwarfs are very, very hot - up to 40 times hotter than our Sun - ranking among the hottest objects in the universe. But they are not incredibly active. All the heat inside of them is trapped and has nowhere to go. Only on its outer layer can it escape into space. But space is mostly empty, so heat can't be transferred by conduction. The only way energy can escape is by radiation. This is so inefficient that white dwarfs will take trillions of years to cool down, which may make them humanity's last refuge. They might be the last sources of light and energy in a dying universe. According to some estimates white dwarfs might shine as long as 100 billion billion years, ten billion times longer than the universe has existed. So far into the future that no regular stars will shine any more, galaxies will have evaporated, and only then will the first white dwarf turn into the first black dwarf. When this happens the last hope for life will die off. Black dwarfs will be inactive spheres with no energy left to give, still massive enough to kill you if you get too close. So cold that they'll be near the coldest possible temperature in the universe, so dark that they are practically invisible. The universe will enter its last stage - heat death - which will leave the universe unrecognizable, an absolutely dark and cold graveyard, with black holes and black dwarfs scattered over trillions of lightyears. We don't know for sure what will happen with black dwarfs in the end. If the proton - one of the fundamental parts of atoms - has a limited lifespan, black dwarfs will slowly evaporate over many trillions of years. If the proton does not decay, black dwarfs will probably turn into spheres of pure ion via quantum tunneling, over a timespan so obscenely gigantic that calling it forever is okay. These ion spheres will then travel completely alone through a dark universe. Nothing new will happen anymore... forever. While this may sound kind of dark, this is so far away that for our purposes today, it might as well not happen at all. It doesn't matter what happens in a billion trillion years. Right now, we happen to exist at an excellent time, able to be in awe about a universe filled with endless stars and light and planets. And enough time to visit them one day. Our music is finally available on Spotify and iTunes. it's composed by our good friends at Epic Mountain, two guys with a studio who make music for a living. You can check them out here, and follow them on Facebook and Twitter. And if you like our videos, please consider supporting us on Patreon. It really would be extremely helpful. If you need an excuse to delay work a little bit longer, here's a playlist with more space videos.
The last question was asked for the first time, half in jest, on May 21, 2061, at a time when humanity first stepped into the light.
http://multivax.com/last_question.html
Nuclear astrophysicist here!
Since this video is going to blow up (pun intended, wait for it), I just wanted to share some fun facts about white dwarfs. Not all white dwarfs will become black dwarfs. Some will fucking explode.
If a white dwarf is in a binary (that means two stars orbiting each other), it can steal mass from its neighbor.
This is because the white dwarf is incredibly compact, so it has strong surface gravity. It's very possible that matter from the neighbor star will actually be more strongly attracted to the WD than to the star it's in, especially when that neighbor star swells in a giant phase.
That stuff that falls onto the WD is mostly hydrogen and helium. As it falls, it gets hot, and after it arrives on the WD it gets buried by the hydrogen and helium that arrives later. So now you've got hot hydrogen being squeezed. This is a fucking time bomb (that was the pun I was telling you to wait for).
That's the recipe for fusion in any star. Take hydrogen, and squeeze. Only now it's happening on the surface of the star, not the core, for all the universe to see.
Once the temperature and density are high enough for thermonuclear fusion, that hydrogen can burn explosively, like a match to gasoline. This is observed as a classical nova. A conflagration consumes the surface of the star, making these dim objects brighten up to the point that new stars seem to appear in the night sky where none was seen before.
Of course, these things are far more frequent than supernova, but far dimmer.
To get a supernova, we need to burn the entire fucking star.
White dwarfs are, as the video says, the corpses of stars like our sun, made of elements like carbon and oxygen. But you can still burn carbon and oxygen (elements 6 and 8) all the way up to elements like iron (element 26) and get energy out.
If a white dwarf gains enough mass from its neighbor, the temperature can get driven high enough to begin burning this carbon and oxygen. We don't know if it happens in the core first, or if it starts like a classical nova that eventually consumes the star, or if it can happen both ways, but the point is this: you can detonate the entire goddamn star in the largest thermonuclear detonation in the universe, the type 1a supernova. You do not pass go, you do not collect 200 dollars, go directly to iron and nickel. In reddit parlance, this kills the star.
For a brief time (a few weeks), these beasts can outshine entire galaxies. This is a picture of SN1994D You see that dot in the lower left? That's a supernova. One star, shining just as bright as many other billions of stars combined.
How fucking dope is that?
Back to your regularly scheduled existential crisis?
When I first watched one of their videos, I couldn't believe the production value. It's on a another level compared to some of the stuff you see on TV. It makes you want to learn new things and that is the most important thing for today youths.
I hope one day someone will take these guys seriously and support them with a lot of money for even better content.
Until then, here is a link to their patreon that helps them make videos.
That went from nice and cheery to unbelievably depressing so fast. One second they were talking about white dwarfs giving off energy basically forever, straight to a universe filled with nothing but dead stars and black holes.
These Kurzgesagt videos are so good they've almost become like a little treat you wait for each month. Really hoping the Youtube advertising controversy isn't affecting his channel.
I feel stupid for asking this question, but where does the universe's energy go in heat death? Or is it just that the cold space between stars is so cold and vast that even if you leaked all the energy out of everything (stars, planets, etc) and into the void, it would just kind of dissipate without causing any real temperature change.
Also, does anyone know of any good sci-fi stories that take place with humanity living during that time period of white dwarfs?
These guys make educational videos better than any tv show I've ever seen.
This is incredible. When I have a kid and he's like 7, I'm putting the little shit in front of the computer and going to play all of their videos. Easy parenting.
why do things tend to form into iron when talking about suns?