If the sun does explode in the far future, what would make it explode?


If the sun does explode in the far future, what would make it explode?

In: Physics

The Sun is a gigantic nuclear reactor. It produces a lot of energy, and in the case that gravity collapses the core, it can release a lot of it at once, in the form of expansion and explosion.

Also our sun won’t explode, bigger stars do though.

Stars generate energy in their cores, and this inflates the rest of the gas in the star like a giant balloon. More massive stars produce more energy and inflate to incredible sizes – near the ends of their lives they can inflate to preposterous volumes larger than Mars’ orbit.

Large stars explode when their core suddenly stops producing enough energy to keep the rest of the star inflated. They collapse inward at hypersonic speed and the catastrophic shockwave when the innards of the star crumple into core obliterates it.

The sun is too small for this, and will fizzle out with a sad stellar fart instead.

The sun is constantly exploding nuclear bombs by fusing hydrogen atoms together to form helium. The large size of the sun causes intense pressures and heat due to gravity at the sun’s core, driving these reactions.

When the sun eventually runs out of hydrogen to fuse, it will start fusing the helium products into carbon and oxygen. This reaction releases more energy than the previous hydrogen reaction, causing the overall size of the sun to expand due to the energy release. This generates a red giant.

Once the helium is all gone, the later reactions are not as powerful and eventually the energy released cannot balance out against gravity. This causes a sudden collapse in the star as gravity pulls it together. In some cases, this single rapid shrinking grants enough energy for one last fusion explosion: a supernova. Supernovas can fuse atoms into various other atoms, providing the building blocks for planets.

Stars are the size they are because the nuclear reactions pushing everything out and the gravity pulling everything in balance each other out. Eventually stars run out of fuel and when they do their nuclear reactions stop pushing things out and gravity will pull everything in. In big stars the gravity pulling everything in so quickly is enough force to cause one last nuclear mega-explosion (called a supernova). Our sun isn’t massive enough to cause a mega-explosion. When our sun finally runs out of nuclear fuel it will shrink to a small, dim, dense ball about the size of earth. This ball is called a white dwarf.

Stars fuse lighter elements into heavy elements. This fusion releases energy and stops the star from collapsing under its own weight. When the star runs out of material to fuse, it collapses. If the star is massive enough, his inward collapse bounces and causes a huge explosion.

Brian Greene did an excellent demonstration of this on Stephen Colbert’s show:

The Sun is a nuclear reactor. It will run low on Hydrogen to fuse in 4-5B years. Then it will become a red giant star, and it will reach out to where the Earth is now. It won’t explode, because it’s not big enough.

The Sun won’t explode (aka supernovae), it’t not big enough for that, but here the process.

Stars like our sun have enough mass that the pressure at their center keep the material there. Meaning that the hydrogen they have in their core stay there and that they will only be able to consume the fuel they have in their core and not the rest in their outer layers.

Stars are in an equilibrium between two forces. The first is the gravity of their own mass trying to squeeze the star inward, and the second is the nuclear fusion that create an outward force. But when a star consume all their hydrogen in their core, the fusion inside stop, and without a outward force, gravity win. The core of the star is squeeze more and more and since it take time for the residual heat to get out of the core (it can take millions of years), the core of the star actually go up in temperature. This heat up the outer layers and like you probably know when something is heat up it become bigger, so that’s what the outer layer does. It grow to massive since and we call the star at that stage a Red Giant.

Now as the core of the star get compacted more and more by the gravity, the temperature rise enough that it can now fuse the helium in the core. Fusion start again, the outward force come back to fight back the graivty. The core get bigger absorbing the heat from the outer layer and the star is not a red Giant anymore, it goes back to looking more like it used to.

But eventually the helium get all consumed and the cycle continue. The core get compressed by the gravity, the star grew into a Red Giant, eventually the temperature in the core get high enough to fuse the next element. Each time the star get bigger and then smaller and then bigger against, it will launch material into space, slowly losing mass. Eventually, the mass of the star isn’t enough to keep the temperature in the core rising, so nothing happen anymore. Usually at this point all the outer layer was blasted away in space and what is left is just a naked core called a white dwarf. That’s what will happen to our sun.

If the star is massive enough, the cycle don’t stop. The core keep rising in temperature and fusion happen with bigger and bigger atoms until you reach Iron. Iron is important because it’s the first element that absorb more energy than it release when fusion happen. So now instead of nuclear explosion that create an outward force, the core start to suck all the heat from the star. Suddenly nothing is stopping gravity, no more fusion to keep the star stable. The star collapse under it’s own mass.

The only thing left that stop that collapse is a force that stop neutron from occupying the same space. The collapsing star smash into that force like a car would crash into a wall and this create the supernovea.

But star can be so massive that even the force that keep neutron from occupying the same space is not strong enough. The star collapse on itself into a black hole. Something so dense that even light can’t escape.

This is perhaps best explained in a video:


The gist is that hydrogen is fused into helium and the gravitational force balances out the nuclear forces. Eventually, hydrogen will run out and the sun will collapse because of gravity. But that will eventually create conditions sufficient enough to fuse helium and re-expand into a red giant.

As others explained, our sun won’t explode. However it will become a red giant and become as large as the orbit of the Earth. (However, the earth will be pushed away, so it may or may not actually engulf the earth. Life as we know it on earth will still end, though).

Not the most educated opinion, but stars don’t explode, at least not by our definition. They collapse, turning into either super novas or black holes. Both of these processes take way too long a time to mimic any sort of explosion you’d see down here on earth.

All the answers are that it won’t – which isn’t really what was asked.

The sun is not massive enough, so what if the sun merged with another rogue star that puts it into the the mass range that would go supernova?

What if it interacted with a wandering primordial black hole? Maybe not quite an explosion, but it would get ripped to shreds, right?

What if it encountered a region of space where some constant in physics was different? Or hit a cosmic string?