The cosmos is not the serene place it first appears… it is full of aggressive offenders

Reported by Colin Stuart

As ultraviolet radiation cascades down from space, Earth’s place as a life-friendly planet is under threat. The surface of our world is bathed in this high-energy radiation, and it penetrates our oceans to depths of 75 metres (246 feet). The damage is catastrophic. The intense glare fries ocean plankton, and those organisms which survive divert all their energy to repairing their DNA rather than photosynthesising. Oxygen levels then drop as carbon dioxide levels rise.

The knockout blow for many larger species comes as dwindling plankton numbers offer scant food resources, with the effect rocketing up the food chain. Thankfully this fictional future is very unlikely, but what would have caused such devastation? The answer is a gamma-ray burst (GRB). They often emit as much energy in a few seconds as our entire galaxy does in a year. If such a volley of gamma rays were to strike our planet, it would rip molecules in our atmosphere apart, releasing an army of ultraviolet photons to devastate the world’s biosphere. Luckily these catastrophic events are rare, particularly in our own Milky Way. In fact, we’ve never observed one in our galaxy. Even if one were to go off, it would have to be aligned almost perfectly with Earth. However, studying them reveals just how violent our universe can be.

THE MOST DESTRUCTIVE OBJECTS

Gamma-ray bursts

Caused either when a massive star collapses into a black hole or when two neutron stars collide, the total gamma-ray energy emitted is 100 trillion trillion times more than the largest nuclear weapon ever tested on Earth.

Supernovae

An explosion which occurs upon the death of a star, supernovae are at least eight times more massive than our Sun. A supernova can commonly release twice the amount of energy as a typical gamma-ray burst.