Chown's Cosmos: The eye of Sauron

Behold the future. Wind the clock forward five billion years and this could be the spectacular death throes of the Sun. It is a long story. Stars, paradoxically, get hotter as they lose heat – or at least their cores, compressed by the steadily accumulating ash of nuclear burning, get hotter. Eventually, in a low-mass star like the Sun, the core gets so hot that the blistering heat puffs out the cool outer envelope to create a bloated “red giant” that swallows its innermost planetary children and renders the rest little more than chunks of blackened slag. As the core gets ever hotter, it triggers new heat-generating nuclear reactions, ones that are not as placid as the ones that powered the star through its youth. The nuclear paroxysms of the dying star concuss the envelope, driving off its outer layers one at a time, so that they sail out across space. And this is what we are seeing here in the case of the Helix Nebula, 700 light years away in the constellation of Aquarius. Imaged by NASA’s Spitzer Space Telescope, the picture shows not the visible light of hot things but the infrared light of cold dust. The core of the star – the tiny white dot at the centre – has now exhausted all its nuclear fuels and has become a “white dwarf”, a super-dense, Earth-sized ember, slowly fading. The blue, green and red show progressively colder expanding shells of dust. And the tiny orange disk at the centre is made from dust blasted from the star’s incinerated comets.