Nothing lasts forever be it cold November rain or the world on which you live. One day our sun is going to die and, in terms of apocalypses, things are going to get super bad no matter what neighborhood you live in. Lucky for us that’s not scheduled to happen anytime soon. Rest assured this is someone else’s problem.
The thing about apocalypses is that many of them are very hypothetical. Nuclear war, climate change, zombies. They may be possible but none of them are guaranteed. The death of the sun? Absolutely guaranteed.
Since we know it’s going to happen one day, and since maybe you’ve had too much positivity and optimism coming your way lately given how joyful the world is, why don’t we take a look at what’s going to happen when the Sun finally does die and what the Unlucky people of Earth can look forward to as it happens.
When Will it Happen?
The sun is made of about 92% hydrogen which is what is undergoing a non-stop fission reaction and creating energy up there all the time. At 27 million° F in its core, the pressure and heat are so intense that the hydrogen is fused into helium. In terms of mass, the sun is about 330,000 times the size of Earth. They barely have a number for the sun’s mass. In pounds, it’s 4.4 followed by 30 zeroes. It’s ungainly.
The sun is going to die once it has used up all of that hydrogen. You can ballpark that figure at about 5 billion years from now. It’s currently about 4.5 billion years old, so it’s not even middle-aged yet.
At this point, you might be thinking, “Oh no, I better check my calendar in five billion years.” Well, don’t worry just yet, because that’s just when the sun will run out of hydrogen. Once the hydrogen has been used up, there are still two or three billion years to endure the death throes of our star.
Our sun is a yellow dwarf star or a G-type main sequence star. In general, any star that is about the size of our sun and undergoes the same type of fusion reaction is a yellow dwarf. But, as the hydrogen is used up it will become a red dwarf and we’ll see more about that shortly. That’s going to be chaotic not just for the sun but for our whole solar system. And it’s not even done at that point. It still has to reach the white dwarf phase and that will be how it dies officially.
How Will the Sun Die Out?
As we already mentioned, the Sun is going to run out of fuel in another four or five billion years. Once all the hydrogen is gone all that’s going to be left is helium. Our sun doesn’t produce the heat or the pressure in its core to start burning helium.
Right now, the massive force of gravity produced by the sun is constantly pulling at the core but the production of helium during the fusion process pushes it back out again in a sort of balancing act. Helium is essentially waste material during the fusion process. The Sun doesn’t need it, and can’t use it. So, like a nuclear reactor here on Earth, it just makes this junk and it sits around because what else is it going to do? At least on Earth we can bury it in a mountain and pretend we don’t need to worry about it. The sun just has to keep it there and eventually, that’s going to become a problem.
As we run out of hydrogen to burn, gravitational forces are going to take over and make the core denser and denser. It will have more helium than hydrogen, and the hydrogen will start burning outside of the core. That’s going to turn a yellow dwarf into a red giant. If you don’t know what a red giant is, you can probably guess from the name that it’s going to be significantly different from what we have right now.
Because the core is going to be essentially dead and Incredibly compressed by gravity, the hydrogen burning outside is finally going to be able to expand instead of being held inside. That expansion is where the giant part of a red giant comes from. No longer bound by those gravitational forces, the sun will grow. It may reach as far as Mars.
What Happens Next?
Once the red dwarf is formed and has expanded as far as it’s going to, the remainder of what’s in the Sun only has a few options. It will burn off the fuel that it can until the red dwarf shrinks down to form a much cooler white dwarf. This is essentially the end state for most smaller stars. All the fuel has been burned up, there is no longer a reaction happening.
For years it was believed this was how our sun would end up for all time, a cold and forgotten lump in space, but computer models suggest that the rest of the sun’s material is going to be vented off into space. This is essentially just gas and dust and can be as much as half of the entire mass of the star, all being let go and creating a nebula in our solar system.
If you’ve seen pictures of nebulae online, and there are some amazing ones that you can look up, that’s what you’re seeing. The guts of a once bright star, illuminated by the last bits of energy from the intensely hot core of that star. In cosmic terms, these are very short-lived, and our sun’s nebula may only last for 10,000 years.
Could the Sun Become a Black Hole?
A massive, dense star can potentially form a black hole when it dies. These huge stars go through the same process our sun is going to go through, burning off all their fuel as the core gets denser and denser. Because of the size of the stars, the mass becomes so dense that when the star explodes it collapses into a black hole. This singularity is so powerful that light itself cannot escape. Anything nearby, including planets, could potentially be pulled in and destroyed.
Stars that collapse into black holes are typically 8 to 10 times the size of our star. Relatively speaking, we have a very small star in our solar system. Not only is the Sun not big enough to form a black hole, but it’s not even big enough to go supernova when it dies or turns into a neutron star. Not that the fate of our solar system is any better or worse off as a result of this, there’s no happy ending to the death of a star for the solar system at large, but no, no black hole will form.
Can Earth Survive?
Obviously, we don’t know exactly how the Sun is going to look as it dies out and changes from a yellow dwarf into a red giant. However, based on what we know of the sun’s current density, its elemental makeup, and things like that, computer models have suggested that the red giant it becomes is going to swallow up Mercury, Venus, and, maybe, the Earth itself.
Again, if you’re planning on being alive in a few billion years, you may want to make preparations for what’s going to happen before the entire planet is swallowed by a red giant sun. To start with, in a few hundred million years, maybe a billion years, Earth will probably become uninhabitable. Some predictions say we have about 500 million years before the heat of the sun gets to be so bad that the oceans boil off and the Earth becomes a massive, inhospitable greenhouse.
The sun has been getting brighter the entire time you’ve been alive. It’s been getting hotter and brighter the entire time the Earth has been around. It’s obviously a slow process, but our sun is brighter than it was in the days of the dinosaurs. In fact, the luminosity has increased 30% since it was formed.
The brightness of the Sun is intimately related to how life on Earth functions. In a billion years it’s expected the luminosity will increase by another 10%. It increases by 10% every billion years. This may lower CO2 levels so dangerously that complex plant life is no longer able to survive. That would effectively kill off most life on the planet.
However, some optimistic researchers believe that this cycle governing CO2 isn’t as temperature-dependent as we originally thought, and plants might actually get another 0.6 billion years before they die off. Isn’t that great? At that point, they believe something called the moist greenhouse transition will be what kills off all the plants, as our atmosphere becomes so saturated with moisture from increased temperatures that plants can’t survive. That’s essentially that 500 million year prediction we mentioned earlier, only on a longer timeline.
Any way you slice it, eventually the atmosphere of the earth will not be able to withstand the power of the Sun and will be stripped away. That will basically be the end of all life here. The Earth will become not unlike Venus; a scorched landscape of unbreathable air chiefly made of carbon dioxide.
Now, whether it’s in a billion years or 1.6 billion years, let’s say the most complex life on Earth has died off. Then in another three billion years or so until that red dwarf event happens. There’s no way that Venus or Mercury will survive that. Scientists aren’t sure if the Earth will get swallowed whole or if we’ll just be right at the border of the new, red sun.
If we do get swallowed by the sun, it will take less than a day to destroy the entire planet. It may just take a few minutes. If we don’t get swallowed, we’re going to be so close that the sun will scorch every single thing on the planet into nothingness except for the iron core. Everything on the surface, the crust, the mantle, all the rock, all the way down will be dissolved.
For fun, some of the outer planets like Pluto may actually end up existing in a habitable realm with liquid water on their surface. Not that life is going to evolve there, or will even have much time to get started, but it is possible.
Long story short, there is no scenario in which the Earth outlives the sun.
Can The Sun’s End Be Stopped?
So, let’s say humans are alive in one billion years. The Sun keeps getting brighter, it’s getting hotter, and as a species, we realize that the end is coming. Is there any way to stop the Sun from destroying us and itself?
The plot of the 2007 movie Sunshine was essentially this. Astronauts headed out into space with the goal of saving the sun by detonating a nuclear device inside of it. In real life, that’s probably not entirely plausible. But keep in mind that we have one billion years to come up with a better idea. You have to hope that technology will improve beyond what 2007 could imagine.
People have pondered the technical challenges of trying to fix the Sun so it doesn’t die. Essentially, this means either getting rid of excess helium or injecting more hydrogen. Most of the solar system’s hydrogen is already in the sun, so finding a substantial supply would be an issue.
The idea of “stirring” the sun has been proposed since the outer layer is not being burned, it’s the inner core that’s being consumed. Much of the exterior hydrogen is being lost and will be vented off into space before it ever gets a chance to be used up in the sun. Any technology capable of mixing it, however, would probably increase the brightness and heat of the sun. One to five million tons of helium per second would need to be vented to make it work.
Other ideas could see the use of lasers to literally cut away hydrogen in an attempt to make several smaller red dwarf stars that burn less intensely but much longer.
Injecting hydrogen directly into the core could cause instability as well, leading to intense flares and temperature spikes. Making smaller suns would drastically reduce their temperatures. In other words, even theoretically, trying to manipulate an entire star is very risky business. But in a billion years, who knows?