11 November 2015

Journeys of a lifetime: Events in a far galaxy tweak your DNA

Billions of years ago, an iron nucleus forged in another galaxy was flung into space at close to the speed of light – headed for your cells

Journeys of a lifetime: Events in a distant galaxy tweak your DNA

TRAVELLER A cosmic ray
ORIGIN A galaxy far, far away
DESTINATION Our atmosphere
DURATION Billions of years, or weeks

Its nursery is the heart of a supergiant star about to explode into a radiant supernova. At a temperature of about 100 million kelvin, atomic nuclei collide and fuse, adding still more heat to the furnace. Just there on the outer edge of the core is our traveller, a product of that fusion: a nucleus of iron.

The star’s core has been growing for a few hundred thousand years. Eventually it gets too big to hold itself together and suddenly collapses, generating a supernova blast of radiation that shreds the entire star. Caught in the explosion, the iron picks up speed, is bounced around by a combination of shock waves and turbulent electromagnetic fields, gains more and more energy as it goes, until finally it breaks out of the fireball and flies free.

This is a gentle beginning. Our iron speeds through space, leaving behind it the dead star’s glowing nebula. It is headed for the centre of the galaxy, where a monster awaits: a supermassive black hole, a billion times the mass of our sun. Swept up by a stream of gas, the nucleus is dragged perilously close to the point of no return, where it would be inevitably pulled through the black hole’s event horizon to who-knows-what beyond. But at the eleventh hour it is caught by the intense magnetic tornado that circles the black hole, catapulted into a jet of plasma, and squirted out at 90 per cent of the speed of light.

The shock …


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