What Happens to White Dwarfs and Black Dwarfs at the End of the Universe? (Kurzgesagt)

TL;DR

White dwarfs, the dense corpses of dead stars, may be humanity's last home before the universe dies, shining for up to 100 billion billion years. About 97% of all stars end this way, including our Sun, leaving a remnant the size of Earth but with half the Sun's mass, so dense a teaspoon weighs as much as a car. Read on to learn how life might survive around one and what a black dwarf is.

Transcript

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 corp... Read More

Key Insights

• 🤩 White dwarfs are dense star remnants, outliving regular stars by shining for trillions of years.
• 🤍 Life around a white dwarf is possible but extreme due to specific conditions.
• 🙂 White dwarfs may be humanity's last source of light and energy in a dying universe.
• 🥶 Black dwarfs, the final stage of white dwarfs, will exist in a dark and cold universe.
• 🖤 The universe's heat death will leave behind black holes and black dwarfs scattered across vast distances.
• 🖤 Proton decay may influence the fate of black dwarfs over trillions of years.
• 🤍 White dwarfs will continue to shine for an incomprehensibly long time, possibly up to 100 billion billion years.

Questions & Answers

Q: What is "The Last Light Before Eternal Darkness" by Kurzgesagt about?

It explains white dwarfs, the dense corpses of dead stars that could be humanity's last refuge before the universe dies. About 97% of all stars, including our Sun, end as white dwarfs. The video traces their trillions-of-years lifespan and their final fate as black dwarfs in a cold, dark universe.

Q: What are white dwarfs and how do they differ from regular stars?

A white dwarf is the leftover core of a dead star. While the Sun is about 100 times its diameter, a white dwarf is only about as big as Earth yet still holds roughly half the Sun's mass. This makes it extremely dense: a teaspoon is about as massive as a car, and its surface gravity is over 100,000 times higher than Earth's.

Q: How does a star like the Sun become a white dwarf?

When the Sun's core runs out of hydrogen, it begins burning helium into heavier elements and sheds its outer layers as a planetary nebula millions of kilometers across. More than half of the Sun's mass is lost into space, and what remains is its former core, a newborn white dwarf. Small red dwarfs reach the same end by quietly burning out over trillions of years.

Q: Could life exist around a white dwarf?

It is very unlikely but possible. Because white dwarfs are so small, a planet would need to orbit about 75 times closer than Earth is to the Sun to have liquid water, which would tidally lock it into permanent day and night zones. Life could be possible at the edges between those zones, and a white dwarf's very stable energy output may make it safer than orbiting many red dwarfs.

Q: Why do white dwarfs shine longer than other stars?

White dwarfs are extremely hot, up to 40 times hotter than our Sun, but not very active, so their trapped heat can only escape from the outer layer. Since space is mostly empty, that heat cannot leave by conduction and only radiates away, which is very inefficient. As a result they take trillions of years to cool, possibly shining as long as 100 billion billion years.

Q: What is a black dwarf?

A black dwarf is the final stage of a white dwarf once it has fully cooled. It becomes an inactive sphere with no energy left to give, near the coldest possible temperature in the universe and so dark it is practically invisible, though still massive enough to be deadly up close. The first black dwarf will only form far in the future, after regular stars have died and galaxies have evaporated.

Q: What happens to white dwarfs in the far future of the universe?

After the universe enters heat death, only black holes and black dwarfs remain, scattered over trillions of light-years. If the proton has a limited lifespan, black dwarfs will slowly evaporate over many trillions of years. If protons do not decay, they may instead turn into spheres of pure iron via quantum tunneling over an almost unimaginable timespan, then drift alone through a dark universe forever.

Q: Why does the video say this dark ending doesn't really matter for us?

Because it is so far away, a billion trillion years off, that for our purposes it might as well never happen. The video ends on the point that we exist at an excellent time, able to be in awe of a universe still full of stars, light, and planets, with enough time to one day visit them.

Summary & Key Takeaways

• Stars like our Sun will end as white dwarfs, lasting for trillions of years.

• White dwarfs are extremely dense, hot, and may support life in specific conditions.

• They might be the last source of light and energy in a dying universe.