What is a Hypernova?

A hypernova is a special type of supernova created when a star at least 40 times more massive than our Sun expends its nuclear fuel and collapses directly into a black hole, ejecting twin plasma jets at almost the speed of light. A hypernova is the most energetic event in the universe, with Sun-sized chunks of matter being converted almost instantly into electromagnetic radiation. If a hypernova exploded in our vicinity of the galactic neighborhood, it could cut the density of the ozone layer in half, presenting a grave threat to all forms of life. Thankfully, the nearest star even theoretically capable of undergoing hypernova is over thousands of light years away. Still, a hypernova may be considered an existential risk to humanity, albeit a relatively low-probability one.

A conventional supernova is very energetic, capable of outshining its host galaxy for weeks or months on end. A hypernova is even more powerful, but significantly more rare – in our galaxy, hypernova only occurs about five times every million years. Like conventional supernovae, hypernovae are a source of heavy elements such as uranium. Normal fusion processes can only create elements as heavy as iron. To create heavier atoms than iron requires temperature and pressure of such intensity that they are not found in the normal operating lifetime of a star, but only upon its death.

It was only recently discovered that hypernovae are the source of the previously mysterious gamma-ray bursts, intense blasts of light which last between a few seconds and a few hours. The shortest gamma-ray bursts occur in star systems composed of only two neutron stars, or a neutron star and a black hole. Neutron stars are extremely dense stellar remnants which release massive energies when they collide with each other.

Because the gravity created by neutron stars and black holes is so strong, star systems based on them have little other material, and when they collide, energy is released from them but not from anything else. In a normal star system, there are substantial quantities of gas and rock surrounding the star, creating a longer-duration burst as the material is “ignited” by the hypernova explosion. Some of these explosions have been blamed for mass extinctions in earth’s ancient history.