PrajwalSood Just a small town guy who gazes out of his window to wonder what's up

Dying Light and Dark Future

Dying Light and Dark Future

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, some places will exist practically forever from a human perspective:

๐—ง๐—ต๐—ฒ ๐—ฐ๐—ผ๐—ฟ๐—ฝ๐˜€๐—ฒ๐˜€ ๐—ผ๐—ณ ๐—ฑ๐—ฒ๐—ฎ๐—ฑ ๐˜€๐˜๐—ฎ๐—ฟ๐˜€โ€ฆ

๐—ช๐—ต๐—ถ๐˜๐—ฒ ๐—ฑ๐˜„๐—ฎ๐—ฟ๐—ณ๐˜€

In a universe, slowly dying a cold death, they could very well be our last hope. 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 theyโ€™re the exception.

For many, precisely speaking 97% of all the stars, the end would be in form of a white dwarf. There are two ways this can happen:

Small stars - so-called red dwarfs - blow out over trillions of years until they eventually quietly become white dwarfs.

๐— ๐—ฒ๐—ฑ๐—ถ๐˜‚๐—บ-๐˜€๐—ถ๐˜‡๐—ฒ๐—ฑ ๐˜€๐˜๐—ฎ๐—ฟ๐˜€ ๐—น๐—ถ๐—ธ๐—ฒ ๐—ผ๐˜‚๐—ฟ ๐—ฆ๐˜‚๐—ป ๐—ฎ๐—ฟ๐—ฒ ๐—บ๐—ผ๐—ฟ๐—ฒ ๐—ถ๐—ป๐˜๐—ฒ๐—ฟ๐—ฒ๐˜€๐˜๐—ถ๐—ป๐—ด.

Imagine the sun as an enormous autoclave 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 Sunโ€™s mass will be lost into space as a spectacular planetary nebula millions of kilometers across.

๐—ช๐—ต๐—ฎ๐˜ ๐—ฟ๐—ฒ๐—บ๐—ฎ๐—ถ๐—ป๐˜€ ๐˜„๐—ถ๐—น๐—น ๐—ฏ๐—ฒ ๐—ถ๐˜๐˜€ ๐—ณ๐—ผ๐—ฟ๐—บ๐—ฒ๐—ฟ ๐—ฐ๐—ผ๐—ฟ๐—ฒ

A white dwarf is born a star corpse. In its former life, its diameter was about 100 times, now itโ€™s only about as big as Earth, but still with about half its former mass. This means itโ€™s extremely dense, a teaspoon of a white dwarf is about as massive as a car. Its surface gravity is over 100,000 times higher than Earthโ€™s. If you tried to land on it, youโ€™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 thatโ€™s not all: since they are so small, a planet would wish to orbit them about 75 times closer than Earth is to the Sun to possess liquid water.

๐—ง๐—ต๐—ถ๐˜€ ๐—ฝ๐—ฟ๐—ผ๐˜…๐—ถ๐—บ๐—ถ๐˜๐˜† ๐—ต๐—ฎ๐˜€ ๐˜‚๐—ฝ- ๐—ฎ๐—ป๐—ฑ ๐—ฑ๐—ผ๐˜„๐—ป๐˜€๐—ถ๐—ฑ๐—ฒ๐˜€

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 really 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.

๐—•๐˜‚๐˜ ๐˜„๐—ต๐˜† ๐—ฑ๐—ผ ๐˜๐—ต๐—ฒ๐˜† ๐˜€๐—ต๐—ถ๐—ป๐—ฒ ๐˜€๐˜‚๐—ฐ๐—ต ๐—ฎ ๐—น๐—ผ๐˜ ๐—น๐—ผ๐—ป๐—ด๐—ฒ๐—ฟ ๐˜๐—ต๐—ฎ๐—ป ๐—ผ๐˜๐—ต๐—ฒ๐—ฟ ๐˜€๐˜๐—ฎ๐—ฟ ๐˜๐˜†๐—ฝ๐—ฒ๐˜€?

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. Its the minuscule surface of the white dwarf that offers respite to the tiny yet a very hot star. But space is mostly empty, so heat canโ€™t be transferred by conduction. Unlike its former self, its energy can escape only by radiation.

This is so inefficient that white dwarfs will take trillions of years to cool down, which may make them humanityโ€™s last refuge. They might be the last sources of light and energy in a dying universe. According to some estimates, white dwarfs can be the beacons of light as long as 100 billion billion years, ten billion times longer than the universe has existed. So far into the longer term that no regular stars will shine any longer, galaxies will have evaporated, and only then will the primary white dwarf star become the primary black dwarf.

๐—ช๐—ต๐—ฒ๐—ป ๐˜๐—ต๐—ถ๐˜€ ๐—ต๐—ฎ๐—ฝ๐—ฝ๐—ฒ๐—ป๐˜€ ๐˜๐—ต๐—ฒ ๐—น๐—ฎ๐˜€๐˜ ๐—ต๐—ผ๐—ฝ๐—ฒ ๐—ณ๐—ผ๐—ฟ ๐—น๐—ถ๐—ณ๐—ฒ ๐˜„๐—ถ๐—น๐—น ๐—ฑ๐—ถ๐—ฒ ๐—ผ๐—ณ๐—ณ

Black dwarfs are going to be inactive spheres with no energy left to offer, still massive enough to kill you if you get too close. So dark, that they, for all intents and purposes are invisible, so cold that they might as well challenge the mercury for bout with the absolute zero. The universe will enter its last stage - heat death - which can leave the universe unrecognizable, an absolutely dark and cold graveyard, strewn across trillions and trillions of kilometers with only black dwarfs and black holes as universe slowly dwells into darkness. Stars that fall short of the mass to make a black hole, might end up as neutron star.

We donโ€™t know needless to say what is going to happen with black dwarfs within 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 balls of ions will hike alone across the ever so silent fabric of space time. Nothing new will happen anymoreโ€ฆ

F๐—ผ๐—ฟ๐—ฒ๐˜ƒ๐—ฒ๐—ฟ โ€ฆ

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 doesnโ€™t matter what happens in a billion trillion years. Right now, we happen to exist at a superb time, able to be in awe a few universe crammed with endless stars and lightweight and planets. And enough time to visit them one day.

Inspiration and References

  • Carl Segan and his works

  • Kurskesagt

  • PBS Space time and the papers they refer to in the description of their videos

  • Last but not the least, wikipedia

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