Humans can survive as long as they have an energy source. In our case, it’s the sun. But eventually, the universe will die. It will be a couple of million years, but it will. On a universal timescale, the sun will be gone in no time! However, there are a few things that, on a human timescale, will last forever! And surprisingly, these things are the corpses of real stars. White dwarfs. They might be humanity’s last hope before the end of the universe. What are these things, how do they form, and how will they die?
Formation
White dwarfs come from stars.
Okay, that’s a bit boring.
Here is a better explanation:
Stars have a limited lifespan, and the lifespan varies with each star, depending on how massive they are.
For example, really massive stars burn through their “fuel” (“fuel” is in quotes here because the “fuel” is really hydrogen fusing into helium) very quickly and die quickly. These stars explode in a fantastic supernova, creating either a neutron star or a black hole depending on how massive the star is.
But those types of stars are the exception. 97% of all stars end their lives as white dwarfs.
There are a few ways how this can happen. The first way is how red dwarfs become white dwarfs, by fusing hydrogen into helium. These aren’t that exciting. They don’t do anything when they die, just sort of… fizzle out.
Medium-sized stars like our sun are more interesting. Inside stars like our sun, fusion is happening. Fusion releases massive amounts of energy. This energy pushes back against the weight of the star, stabilizing it.
When a star runs out of hydrogen in its core, it begins to fuse helium into heavier elements. While doing so, it will shed over half its mass in a spectacular planetary nebula.
What remains is a white dwarf, about the size of the Earth. The white dwarf is extremely dense. A teaspoon of white dwarf material is about as massive as a car. Its surface gravity is over 100 times as strong as Earth’s.
So, is it possible to survive around a red dwarf?
Life
Life around a white dwarf is unlikely, but plausible. But since most white dwarfs formed from stars that violently died, it’s unlikely that any planets survived. But that’s not all. Since a white dwarf is so much smaller and gives off less heat than an actual star, A planet would need to orbit 75 times closer than the earth is to the star to have liquid water.
This proximity has pros and cons. For one, the white dwarf’s immense density and gravity will totally lock any planet in the habitable zone, giving the planet a permanent day and night side. That means that one side will be a desert, and the other, a freezing tundra. But right down the middle could be the sweet spot for life to thrive!
On the other hand, white dwarfs have a pretty stable energy output, and are pretty safe! Definitely safer than red dwarfs, which vary a lot in energy output, which is deadly for life.
This is still hypothetical, but if we can find the right white dwarf with the right conditions to settle around, we could have a civilization for many millions of years.
But why do white dwarfs shine so much longer than other types of stars?
White dwarfs are very, VERY hot, up to forty times hotter than the sun, ranking one of the hottest objects in the universe. But they aren’t very active. All the heat inside them is trapped and has nowhere to go. Only on its surface can the heat escape. Bur space is mostly empty, so heat can’t actually “latch on” to anything to transfer itself. The only way energy can escape is through radiation. This is so very insignificant that it takes trillions of years to cool down, meaning that they might be the only warm things in the universe trillions of years from now, making them humanity’s last refuge. They might be the last sources of light in a dying universe.
According to some estimates, white dwarfs can shine for over 100 billion billion years, 10 billion times longer than the current age of the universe! So long that all normal stars would be gone, galaxies would have evaporated, and only then will the first white dwarf turn into the first black dwarf. When that happens, any hope for life would be extinguished. The universe will enter its last stage of life — heat death — leaving the universe unrecognizable. In this phase, the universe would look like a few black dwarfs and black holes scattered over trillions of light-years.
Nobody knows what happens with black dwarfs in the end. It’s theorized that the proton actually has a limited lifespan, and if that’s true, black dwarfs will slowly decay over trillions of years.
If the proton doesn’t actually decay, then black dwarfs would slowly turn into spheres of iron via a complex process called quantum tunnelling. Then these dark metallic spheres will drift through empty space forever.
Conclusion
While this might seem sort of dark, it’s so far into the future that for our purposes, it might not happen at all. It doesn’t really matter what happens in a billion trillion years. Right now, we happen to live at an excellent time, and let’s enjoy! I hope you learned a lot!
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