Sure, man-made fireworks displays are exciting to watch, but they’ve got nothing on the massive light-shows put on by dying stars, or supernovas.
About once every second, somewhere in the known Universe, a star explodes. These massive explosions can shine more brightly than entire galaxies full of stars and, in a brief period of time, expend more energy than our own Sun will over its entire lifespan.
A supernova event is actually a massive scale nuclear reaction that occurs when a star becomes unstable. This can occur for one of two reasons. In the first, the star draws in matter from another nearby star until there is too much energy to contain, resulting in a type I supernova. In the second, the star runs out of nuclear fuel and collapses under its own gravity, resulting in a type II supernova.
These explosions, while destructive, are necessary to life in the Universe, because they expel the elements that are the building blocks of planets.
Not every star is capable of going supernova, though. Our own Sun, for instance, doesn’t have enough mass. Though it is large by our own reckoning, it is actually a relatively small star in the grand scheme of the Universe. Instead, our Sun is expected to swell into a red giant, swallowing up and incinerating our own planet in the process, when it runs out of fuel. While that prospect may sound terrifying, rest assured that the Sun has a few billion years left before it tires out.
To explode into a supernova, a star needs to be much larger than our Sun — about 10 to 15 times larger. Astronomers think that stars even larger than that — yes — they come even bigger — also don’t explode, but rather collapse into black holes.
The night sky is filled with the remnants of supernovas past. For instance, the much-celebrated Crab Nebula is thought to be the visible remains of a bright supernova recorded by Chinese astronomers in 1054 in the same region of the sky.
With an average of only one supernova event every 50 years in our own Milky Way, though, you might not want to cancel your Independence Day plans.
Watch this video of a supernova exploding!