Sunday Science: Supernovae

The Crab Nebula is the remnant of a supernova explosion at a distance of about 6,000 light-years, observed almost 1,000 years ago, in the year 1054. It contains a neutron star near its centre that spins 30 times per second around its axis. Credit: ESO

If a star has enough mass, it will explode in a monumental supernova explosion at the end of its life.

When a supernova occurs, it burns brighter than an entire galaxy and radiates more energy than our Sun will in its entire lifetime, all within just over a minute. According to NASA, supernovae are “the largest explosion that takes place in space.”

​For a supernova to happen, the star must be between eight and 15 solar masses. One supernova also occurs roughly every second in our universe, but you can't see them all. In fact, a supernova occurs in our galaxy once roughly every 50 years.

Most of the universe's chemical elements are also made in a supernova thanks to the phenomenal heat and pressure in these explosions.

There are two ways a star can go supernova.

Type I supernovae

A star can pull matter from a nearby neighbour until it has sufficient mass that a runaway nuclear reaction starts and ends in a supernova explosion.

For a Type I supernovae, a White Dwarf usually pulls matter from its companion star in a binary system and builds up enough mass to go supernova.

Type 1 supernovae are thought to blaze with equal brightness at their peaks, so they are used by astronomers as "standard candles" to measure cosmic distances.

Type II supernovae

A large star runs out of nuclear fuel and collapses under its own gravity. But, instead of ballooning to a Red Giant and contracting to a White Dwarf, it explodes in a supernova. 

Before it reaches the supernova stage, heavier elements gradually build up in the centre of the star. The star forms layers, like an onion, with the heavier elements sat at the centre and the lighter ones towards the outside.

Once the star has built up enough mass (and passes something called the Chandrasekhar limit) the star implodes. The core heats up and becomes even denser before the outer layers are thrown off in a dramatic supernova explosion.

A neutron star is left behind. We'll look at neutron stars next week.

If the original star is 25 times more massive than our Sun, a black hole is left behind. And if the star is more than 100 times more massive than our Sun, nothing is left behind. The star just explodes and leaves nothing behind.

Extra reading and watching

LEFT: Just before a Type II supernovae explosion, the star is layered like an onion with increasingly heavy element. Iron(man) sits at its core. TOP RIGHT: Before a Type Ib supernova, the outer hydrogen layer is missing. BOTTOM RIGHT: Before a Type Ic supernova, the outer hydrogen and helium layers are missing.

I've oversimplified here as there are three subsets of the type I supernovae: Ia, Ib and Ic. The Ia category supernovae begin as the binary systems we described earlier where the White Dwarf pulls matter from its companion.

Type Ib and Ic supernovae are caused by the implosion of massive stars that have already shed some of their outer layers. Type Ib has lost its hydrogen layer and Type Ic has lost its hydrogen and helium layers.

But supernovae don't like to conform. For example, a very bizarre supernova was recently detected that explodes again and again.

NASA also managed to catch a supernova explosion with the Kepler Space Telescope last year. This animation was produced from the telescope's data as it recorded the supernova:

What is Sunday Science?

Hello. I’m the freelance writer who gets tech. I have two degrees in Physics and, during my studies, I became increasingly frustrated with the complicated language used to describe some outstanding scientific principles. Language should aid our understanding — in science, it often feels like a barrier.
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So, I want to simplify these science sayings and this blog series “Sunday Science” gives a quick, no-nonsense definition of the complex-sounding scientific terms you often hear, but may not completely understand. 

If there’s a scientific term or topic you’d like me to tackle in my next post, fire an email to gemma@geditorial.com or leave a comment below. If you want to sign up to our weekly newsletter, click here.