Supernovas are such massive violent explosions that they can create and change the very nature of elements, scattering them into the universe to be absorbed by new planets, stars, and even life itself.
That all sounds great — unless it happens in your cosmic backyard. If our own Sun were to go supernova, it would certainly take Earth along with it.
But could our Sun ever go supernova? The easy answer is no, because it lacks either of the two main conditions that can cause a supernova.
“Our Sun can’t go supernova because it is too small to have its core collapse, and it doesn't have a binary companion to steal matter from when the core of ash is left over as a white dwarf,” says Andy Howell, an astronomer at Los Cumbres Observatory in California.
What Is a Supernova?
In short, a supernova is a colossal explosion. (NASA describes a supernova as "the biggest explosion that humans have ever seen.") These explosions manifest as brilliant bursts of light when a massive star reaches the end of its life.
Notably, supernova are also the main source of heavy elements in the universe. As these stars collapse, they generate a shockwave that can trigger fusion reactions in the star's outermost shell. Those reactions then produce new atomic nuclei, a process known as nucleosynthesis.
When a star goes supernova, the elements forged through this process — as well as those stored within the star's core, including carbon and nitrogen — are distributed throughout space.
Read More: Is Betelgeuse About to Become a Supernova?
What Causes a Supernova?
Truly massive stars can go supernova when they run out of fuel. During the healthy part of a star's lifespan — about where our Sun is currently — stars burn hydrogen until it fuses into helium. Gravity compresses the hydrogen to such a large degree that the element actually changes.
This produces an enormous amount of energy, but once the hydrogen in the center runs out, the ante is upped: Stars pass what's known as the "main sequence" phase and begin to turn into red giants. As there is no hydrogen left in the center, the star will begin to fuse helium into carbon, nitrogen, and oxygen — heavier elements than helium.
During this whole time, the star will be puffing up, pushing its outer layer outwards —against the force of gravity that pulls it back. If this occurred to our Sun, for example, the expansion would likely swallow up the inner plants — potentially including Earth, says Howell.
What Happens After a Supernova?
What happens next depends on the size of the star. In larger stars — say roughly five times the mass of our Sun or more — the pressure of the gravity is enough that elements like oxygen and carbon will fuse into metals like iron and nickel. But once the fuel is gone, the star will begin to cool.
This means that the pressure pushing the outer layer away from the core loses power against the gravity pulling it in. Thus, the star eventually collapses on itself, causing a supernova explosion.
Read More: What Happens When a Star Dies?
Are There Different Types of Supernova?
The supernova just described is sometimes referred to as a type 2 supernova. But there is also another kind, called a type Ia (pronounced “one-A”). This supernova only occurs in solar systems with two stars — one of which is a white dwarf.
While the details can get a bit complicated, the white dwarf will essentially steal matter from the other star, says Howell. White dwarfs are usually relatively inactive, but this process reignites them. “Tidal forces can strip the matter from that other star,” adds Howell.
The increase in mass and energy can then lead to a supernova, leaving the star as a neutron star or a black hole.
Read More: This is What a Black Hole Sounds Like
Will Our Sun Ever Go Supernova?
Our Sun doesn’t match the requirements for either of these two types of supernova. It’s the only star in our solar system, for one — so we couldn’t have a type Ia.
What's more, the Sun isn’t anywhere near large enough to go supernova without another star. Instead, once the core of our Sun has burned all its hydrogen and helium to become a mixture of oxygen and carbon, it will likely become a red giant for a period before cooling down into a white dwarf.
“Our Sun will basically continue to fuse hydrogen to helium, up to carbon and oxygen, then it will be left as a ball of carbon and oxygen, and continue to die down,” Howell says, adding that this may occur in roughly 5 billion years. “Because the Sun is not massive enough, the Sun will not have the pressure of these outer layers.”
Read More: Here's What Happens to the Solar System When the Sun Dies
Are Supernovas Destructive?
The explosions unleashed by supernovas are among the strongest known in the world. The energy is so massive, that the exploded star can be converted into an ultra-dense neutron star or a black hole. The Crab Nebula is an example of a supernova that was observed exploding by some Chinese astronomers nearly on millennium ago. The crab pulsar visible by powerful telescopes today is a neutron star that sits at the center of this nebula.
The force from these explosions can damage atmospheres of other planets, perhaps as far as 160 light years away. For context, even the seemingly-far-flung Pluto isn’t anywhere near a single light year from Earth.
Read More: How Many Ways Can the Sun Kill Us?
While violent, supernovas are very important for the genesis of the elements created in the massive explosions. The large majority of the elements that make up the human body were created in supernovas. Even the iron in your blood, for example, came from these cosmic explosions — long before our own Sun was a glimmer in the sky.
“They are really responsible for the material that makes us,” Howell says. “This process of supernovae is important to our existence."
Still, for better or for worse — and for life on Earth, it's certainly for the better — our Sun won’t be participating in that process.
Frequently Asked Questions About Supernovas
What Does a Supernova Look Like?
A supernova appears as a bright, expanding burst of light in the sky. Initially, it can outshine entire galaxies and is visible even in daylight. As it evolves, the supernova's appearance changes, often forming a nebulous, glowing shell of gas and dust.
How Hot Is a Supernova?
At its core, a supernova can reach temperatures of several billion degrees Celsius. This extreme heat is a result of the immense energy released during the explosion, which is powerful enough to fuse atomic nuclei.
How Long Does a Supernova Last?
The visible light from a supernova can last from a few days to months. However, the aftereffects and the remnant can persist for much longer.
When Was the Last Supernova in the Milky Way?
The last known supernova in the Milky Way occurred in 1604 and is known as Kepler's Supernova. It was observed by Johannes Kepler and is the most recent supernova in our galaxy to have been observed with the naked eye.
When Is the Next Supernova?
Predicting the next supernova is challenging due to the unpredictable nature of these events. However, given the estimated rate of supernovas, it's statistically probable that one might occur within the next few decades. Astronomers have predicted Supernova Requiem to appear in the year 2037.
