Stars are some of the most abundant astronomical objects in the universe – overall, astronomers believe that there are around 200 billion trillion stars!
But nothing lasts forever and even stars have their own expiration date. Eventually, stars come to the end of their life and die, but some die with a bit more flare and drama than others. These stars die in a huge explosion called a supernova.
So what exactly is a supernova and how long do they last? Seconds? Hours? Years?
To find out the answer, keep on reading and find out a bunch of cool facts about supernovas!
What Is A Supernova?
Supernovas occur at the end of a star’s life. They are huge explosions and are the biggest explosions that us humans have ever seen. Supernovas are so powerful and bright that many astronomers refer to them as the ‘last hurrah’ of a dying star.
However, not every star dies in a supernova – only large stars that are about five times the size of our Sun have enough energy to go out with a bang! This is because a star needs a certain amount of energy to be able to go supernova and not all stars are large enough to do that.
Supernovas happen because massive stars burn huge amounts of nuclear fuel at their cores, producing tons of energy that makes the core burn at very high temperatures. The heat from these high temperatures creates a lot of pressure that pushes outwards.
The outward heat pressure of the core is balanced by the inward push of gravity. The star’s own gravity tries to squeeze the star down into a tight ball but is resisted by the heat pressure that wants to push outward and expand.
This is how stars keep their shape – the two forces live in balance, pushing against the other.
But when the core runs out of nuclear fuel to burn, it begins to cool down and the outward heat pressure starts to drop. Suddenly, the two forces are no longer balanced – gravity wins and pushes the star down into a ball, and the star collapses.
The collapse of the star creates a huge shock wave and explosion – known as a supernova!
So How Long Do Supernovas Last?
Supernovas only take seconds to happen, from start to finish, but we view them a little differently on Earth.
The moment the two opposite forces of pressure and gravity are thrown out of balance, the star collapses in around 15 seconds. This part depends on just how massive the star is as the smaller the star, the quicker it will take for it to fully collapse.
But overall, stars collapse very, very quickly and the shockwave that comes afterwards only lasts a few minutes. Supernovas are bright and powerful but they don’t last very long.
However, we have a different view from Earth.
Most supernovas that astronomers get to observe are happening outside of our galaxy, but our view is often blocked. Supernovas are also not very common, but they appear in telescopes as a star gradually getting brighter and brighter over the course of a few weeks or even months.
Eventually, once a star has reached its peak luminosity, it starts to fade away – and after a few years, the star is no longer visible.
From Earth, it looks like supernovas last for months when actually, they take just seconds to happen. This is because the radioactive material produced in the supernova keeps emitting energy and thus – light.
Supernovas can leave behind remnants that can remain for thousands of years, so for us here on Earth, it looks as though a supernova can last months – but it does not. Supernovas can last for anything between a few seconds to a few minutes, but they glow in our telescopes for months.
What Happens After A Supernova?
After a supernova is over, the very dense core of the star is left behind surrounded by a cloud of hot gas that once formed the star. The hot gas is referred to as a nebula.
In smaller stars, some astronomers mistakenly believed they saw a planet instead of a dead star – so some nebulas that are formed by smaller stars are called planetary nebulas instead. They actually have nothing to do with planets – it was just a mistake the astronomers initially made.
But nebulas are not the only thing left behind by a dead star. The largest and heaviest of stars can leave behind the densest object in our universe: a black hole!
A black hole is not actually a hole. They are the core left behind by stars that are at least ten times the size of our Sun. Because their mass is so huge, their gravity is also incredibly strong and black holes pull a lot of space matter towards them. Nothing can escape a black hole’s pull – not even light.
That is why to our eyes, these dense dead star cores appear as – well, black holes! – because light cannot reflect off it and into our eyes. So, we cannot visibly see a black hole but we know that it is there because we can see its effect on other space matter.
Do All Stars Go Supernova?
No – unfortunately, not all stars get to go out with such a bang.
Our Sun is one of them. Some stars are just too small to create such an explosion when they die.
For a star to go supernova, it must be at least several times more massive than our Sun. Most astronomers estimate that a star should be at least 8 to 15 times more massive, but none can agree on an exact solar mass.
So how do these smaller stars die?
Well, some just literally sputter out once they use up all of their energy. It burns brighter and then all of a sudden – it’s gone, leaving behind a lump of matter to just hang around in space. It’s not a very dramatic way to go.
Stars that sit in the middle (too small to go supernova, but too large to just give up the ghost quietly) become a red giant star. This is the fate our Sun will face in a couple of billion years.
These stars will first begin to shrink as it enters the last few stages of its life and begins to use up all its energy. The shrinking core then begins to heat up, bringing temperatures and pressures to a significant level to ignite again. The outer layers of the star start to swell up and cool down the further they get away from the star – eventually turning red.
Astronomers believe that when our Sun starts it’s red giant phase, it will swell up and nearly reach the Earth’s orbit!
A star will burn in its red giant phase for another billion years before it will either go supernova like other stars, or cool down and shrink into white dwarf stars if the star is still not large enough to go supernova (this is likely what will happen to the Sun).
So how long does a supernova last?
Supernovas are basically an exploding star, and it only takes a few seconds for the core to collapse and the shockwave to blast stellar material outwards into a nebula. Supernovas can also leave behind radioactive remnants that give off a lot of energy, making a supernova glow for months through our telescopes here on Earth.
Due to ongoing research, we are constantly learning more and more things about stellar phenomena like supernovas – so stay on the lookout for any new announcements from astronomers!
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