How Will the Sun Die?

(Last Updated On: October 29, 2020)

Well it’s not time to get into the spooky spirit without a heaping of existential dread, right? Apparently it’s not a too uncommon experience for us to have had the existential dread of the Sun exploding as kids. Point is, the Sun exploding is an important consideration of mortality for at least a good handful of us–especially if we haven’t yet gotten a grasp of how stupid long it will be before the Sun dying even enters the radar for “things to deal with.” But let’s indulge in the thought experiment for a bit. When the Sun one day goes, what’s gonna happen? How will the Sun die?

How the Sun Lives

Perhaps it may be relevant to talk a bit about how the Sun actually works. Broadly speaking the Sun is a giant (roughly 1.9e30 kg, also known as 2 with 30 zeros after it) fusion reactor that generates energy. Which is like the opposite of how modern nuclear reactors work–which do so through fission (splitting atoms). 

Anyway, it’s this fusion that gives each star their energy and, for us scrubs on Earth, gives us everything we have on Earth. Stars do have a finite amount of stuff to fuse–and that affects their size and color. 

As far as our Sun is concerned, it’s fusing hydrogen into helium into its core. It’ll continue doing so for a projected ~5 billion years. Also known as, the future of the Sun is not going to be relevant to anyone reading this post. Contrary to that time Gary Johnson said we shouldn’t deal with climate change because the Sun will expand in 2016

What Happens in 5 Billion Years?

Right now the Sun is fusing hydrogen with hydrogen–which if you’ve seen a periodic table, you know hydrogen is basically just a proton and an electron. Hydrogen is fused into helium, which is, you guessed it, two protons and two electrons (and also two neutrons). 

We know that, eventually, the Sun will eventually run out of hydrogen. To power itself, it will have to fuse something else–which in this case is helium. Helium gets fused into carbon and for many stars we move down the periodic table until it’s too much energy to keep the fusion going. With some exceptions, it’s a sufficient generalization to say that it takes more energy to fuse helium into carbon than it takes to fuse hydrogen into helium. 

Depending on the star, heavier elements can be fused within the star’s core (where the fusion occurs). That’s where we get a lot of important and common elements like oxygen and iron in the universe. 

Anyway, once we get into fusing helium into carbon (opposed to hydrogen), we open some new pathways. Carbon can be used with some other helium lying around to create oxygen or even some hydrogen to create nitrogen. 

If you understand nuclear chemistry and do some math, you probably figured out that these pathways also create some spare neutrons that can’t stick around for a long time. But these allow for other pathways to fill out even more of the periodic table. 

By this point, the Sun is fusing mostly through the helium pathway, and it’s a red giant now. Nothing like the Sun we know and love today. By this point, Earth will largely be incompatible with life. In becoming a red giant, it will balloon in size, swallowing Mercury, Venus, and likely Earth. Hopefully we’ll have figured something out for that in 5 billion years.

For more perspective on stellar sizes, here’s some further reading: What Is the Biggest Star?

The Stuff We Have

As an aside, a lot of the most common naturally occurring elements on Earth can be tied back to the Sun. You know, stuff like hydrogen, carbon, nitrogen, and oxygen. Which is pretty neat–it’s all a byproduct of our Sun’s formation. There’s also the Big Bang, such a massive release of energy that we get the fusion and creation of a lot of early elements too!

Anyway, it’s just pretty neat. 

Explosions!

You’ve probably heard of the legendary supernova, the final hurrah of a dying star as it collapses in on itself. Perhaps the formation of an all-consuming black hole

For our Sun, it won’t be seeing such a cosmically powerful end. 

When it becomes a red giant, it will do so for about a billion years, burning helium as the last of the hydrogen within it depletes. Yeah, the red giant phase is a lot shorter than the rest of a star’s life cycle. 

Eventually the Sun will fuse more and more heavier elements like carbon and oxygen–ones that basically take more energy to create than the Sun can reasonably continue recycling for more fusion. With nothing left to fuse, the Sun will shrink once again.

It’ll shrink a lot–and not just by deflating in the same way it will inflate when it becomes a red giant. 

All that stuff around the Sun’s core? It’ll just be ejected in a cosmic puff of stellar gas. It’s significantly more violent than a little poof, but it’s significantly less violent than a supernova. 

The ejected gasses, which might be as much as half the Sun’s mass at the time, will give us a planetary nebula. We’ve seen these with other stars before too–some are quite pretty.

What’s Left?

After the Sun ejects some 50% of its mass, all that will be left is its core. It’ll be a roughly Earth sized ball, but packed way more densely. Like 200,000 times more. Which means standing on a white dwarf (barring the fact that you would definitely burn to death) would have you weighing 350,000 times what you weigh on Earth.

As a white dwarf, the Sun will continue to peddle away for a long time, until it radiates all its heat and energy away into the cosmos, becoming a dead, black dwarf. At least in theory, the calculated time for a white dwarf to fizzle out is longer than the current age of the universe. 

You can celebrate the Sun with some Beatles lyrics here.

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About Kyler 728 Articles
Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.