Nebulae · planetary

The Helix Nebula: what will happen to the Sun

The Helix Nebula, a ring of orange and red gas round a blue-green centre, drawn in Exo-View

The Helix Nebula is the shell of gas a dying star shed about 10,000 years ago, 655 light-years away in the constellation Aquarius, with the hot core of the star, a white dwarf, shining at its centre. The Sun will do the same in about five billion years, so the Helix is a picture of our own future.

Fly to the Helix Nebula Fly to the Sun

Distance: About 655 light-years
Width: About 2.9 light-years, over half the Moon's width on our sky
Kind: Planetary nebula, nothing to do with planets
Catalogue number: NGC 7293
Age: About 10,000 years
Centre: A white dwarf, the star's bare core, at about 100,000 K

Why 'planetary'?

Nothing in it is a planet. William Herschel called such shells 'planetary nebulae' in the 18th century because through his telescope they were round and greenish, like the disc of Uranus. They are the final act of stars from about 0.8 to 8 times the Sun's mass.

How a Sun-like star dies

When a star like the Sun runs out of hydrogen to burn at its core it swells into a red giant and, over a few hundred thousand years, throws off its outer layers. What is left is the core, a white dwarf about the size of the Earth, white-hot, and so hot that its ultraviolet light makes the surrounding gas glow. A shell like this lasts about 10,000 to 20,000 years before it thins away into space.

The Sun is due to swell into a red giant in about five billion years. It will swallow Mercury and Venus, and perhaps the Earth, and then leave a nebula like this one round a white dwarf.

Thousands of comet-shaped knots

The Helix is close enough that telescopes see details in it: about 20,000 small knots of gas, each with a tail pointing away from the star like a comet, each about the size of our solar system. Its nickname, the Eye of God, comes from how it looks in photographs: an eye with a bright blue-green iris and a white pupil.

In Exo-View

The key below flies from the Sun to the Helix Nebula, a ring of orange and red round a blue-green centre. The shape is drawn from the nebula's photographs, an artist's impression, and the plate says so.