Supernova

This bright object in space is a star – a gigantic ball of extremely hot, ionised gases. The ionised gases are held together by an immense gravitational force that pushes them inwards, towards the star’s centre. There, in the star's core, the pressure is so high that nuclei of lighter elements combine to form heavier elements. This process is called nuclear fusion. Nuclear fusion produces so much energy that it pushes outwards and counteracts the gravitational force.

This fine balance between gravitational force and energy from nuclear fusion allows the star to exist. But only as long as there are gases that can act as fuel to run the nuclear fusion. Over time, the fuel burns out, and the gravitational force overpowers the energy pushing outwards. The star reaches the end of its lifetime. And that’s what’s happening to this star right now.

This star is an especially large one — it’s more than eight times the mass of our Sun. Stars this big or bigger are known as massive stars. In a massive star, gravitational force is extremely large. When the nuclear fuel burns out, there is no more energy produced to counteract the gravitational force. The overpowering gravitational force causes the star to collapse inwards within seconds!

What used to be the star's core becomes extremely dense. In massive stars between eight to ten times the mass of our sun, the remains of the core form a very small but dense neutron star. Cores of massive stars bigger than that, are likely to turn into a black hole instead. The rapid collapse of a star produces a huge shock wave. The shock wave, in turn, causes the still collapsing outer part of the star to explode.

This powerful explosion that follows the collapse of a star is a supernova. A supernova shoots the debris of the star out into space, forming an expanding cloud of hot gas — a nebula. Eventually, the chemical elements from the nebula combine to form new stars, planets, and everything else in the universe. A massive star exploding at the end of its lifetime is one way a supernova can occur. Another type of supernova explosion can happen when two stars orbit one another.

One of them needs to be a small dense star at the end of its lifetime — a so-called white dwarf, that’s similar in mass to our sun. The other star has to be much larger. In such a case, the gravitational pull of the white dwarf might attract, or "steal", matter from the bigger star. When the white dwarf accumulates enough stolen matter to reach about 1.4 times the mass of the Sun, it explodes as a supernova! Scientists who study space can learn a lot about the universe from supernovas.

But you don’t need to be a scientist to see a supernova. Whether resulting from the explosion of a massive star or a white dwarf, all supernovas emit large amounts of radiation, some of it in the spectrum of visible light. Supernovas are so powerful that they can sometimes be observed as bright, star-like spots in the sky. They can outshine all other stars, and some could be bright enough to be visible even during the day! Who knows, maybe you’ll be lucky enough to spot one someday!