What If Our Sun Became a Black Dwarf?

What if instead of shining brightly for another 5 billion years, the only star in our Solar System turned into a dark and cold remnant? A black dwarf.

How long would the Earth last without all the heat and light it gets from the Sun? What would happen to the rest of our Solar System?

And how would the Sun going dark change the Universe? All stars have an expiration date: they don’t just fade to black, though. Giant ones, ones that are at least ten times bigger than our Sun, explode in supernovas and collapse into neutron stars.

Stars like our Sun don’t have enough mass to become a neutron star. They end up expanding to red giants and then shedding their outer layers until only their core remains. That’s when they become white dwarfs.

Unlike hydrogen-burning sunlike stars, white dwarfs don’t have fusion reactions fueling them up. They gradually cool down, radiating whatever energy they have left. Until one day, theoretically, they become black dwarfs. The thing is, there are no black dwarfs anywhere in the Universe…

Black dwarfs just haven’t formed yet. You see, white dwarfs may not produce any energy, but they have still enough of it left to keep them shining, faintly, for hundreds of billions of years.

Given that the Universe is only 13.8 billion years old, even the oldest white dwarfs are still glowing at temperatures of a few thousand degrees Kelvin.

In the case of our Sun, it will take another quadrillion years for it to cool down and become a black dwarf. That’s one million million million million years from now… give or take a few millions.

Think that humans will be around for that long? Well, let’s switch it up. What if the Sun burnt out tomorrow?

I hope you have good supply of batteries on hand because the entire Solar System would be thrown into darkness. Put on a few sweaters, because it would become much colder, too.

Planetarily speaking, we’re pretty spoiled here on Earth. With all the heat and light provided by the Sun, we’re able to make a comfortable home on a rock hurtling through space at 110,000 km/h (68,000 mph). It’s easy to forget that we’re just another speck in the Universe. But if the Sun stopped burning, it would be immediately evident that we’re just floating in space.

After the first week without the Sun’s heat, the Earth’s surface temperature would drop to 0°C (32°F). After a year, it would go down even more – dropping to a freezing cold -100°C (-150°F).

By that time, all our oceans would be covered in ice. Despite that, the only warm place on the planet that you’d have even a slight chance for survival would be near the Earth’s geothermal vents at the bottom of one of these oceans.

That is, if the Sun turned into a black dwarf instantly, which is unlikely even for our hypothetical scenario.

Realistically, to become a black dwarf, the Sun would have to go through all stages of the stellar life cycle. From the main-sequence star it is now, the Sun would expand into a red giant, fade out to a white dwarf state, and only then cool down to become a black dwarf.

At the red giant stage, it would bake the Earth. Most likely, swallowing it completely along with Venus and Mercury. Oops. At least we wouldn’t have to worry about freezing to death once the Sun shrank to a black dwarf.

What about the rest of the planets? The ones lucky enough to have evaded the burning flames of the red giant?

Well, they’d keep orbiting the remnant of the Sun as if nothing had happened. Even though the Sun would shrink to the size of the Earth, its mass would stay the same, meaning that its gravitational pull would remain unchanged.

In the grand scale of the Universe, the death of the Sun wouldn’t change anything either. The Sun would be just another star to go dark, too small and insignificant to make the Universe even a tiny bit darker.

But what if all the stars died at the same time?