Helix Nebula: A Nearby Dying Star in Aquarius

What is the Helix Nebula?

The Helix Nebula is also listed as NGC 7293 or Caldwell 63 ¹. It sits in the constellation Aquarius ¹². It belongs to a group called planetary nebulae, which have nothing to do with planets.

The name describes how they look in small telescopes. In plain terms, it is a shell of gas let go by a star of middling or small mass near the end of its life ¹. Seen from Earth, the gas forms a ring that some people link to an eye.

Because of that look, it has sometimes been nicknamed the Eye of God and the Eye of Sauron in popular culture ¹. Its form is said to be much like the Cat's Eye Nebula and the Ring Nebula ¹. The light we see comes from the hot core left behind. That core warms and lights the gas around it.

Where is it and how far away?

The Helix is among the nearest bright planetary nebulae to us ¹. One listing gives the distance as 201 parsecs ². A space mission called Gaia measured 655±13 light-years, often rounded to about 650 light-years ¹.

It was found by Karl Ludwig Harding ². The listed year is 1824 ², while another account says the find was most likely before 1824 ¹.

The cloud is about 2.5 light-years wide, or about 0.8 parsecs ¹. Its age is put at about 10,600 years, with an upper range of 2,300 years more and a lower range of 1,200 years less, based on size and a spread speed of 31 km per second ¹. Researchers picture it as a stretched ball tipped toward us by about 21 to 37 degrees, with thicker gas around its middle ¹.

What makes it special to scientists?

The Helix was the first of its kind where small comet-like lumps were seen ¹. Similar lumps have since been found in a few other near planetary nebulae with gassy outer layers, such as the Ring Nebula and the Dumbbell Nebula ¹. The Helix is thought to hold about 40,000 of these knots ¹.

Each lump has a cool gassy heart ¹. The side facing the central star looks brighter, and a faint tail points outward ¹. Without the tail, each lump is roughly as wide as our Solar System ¹. One idea is that fast, thin, charged gas is pushing into slower, thicker gas thrown off earlier, creating these shapes ¹.

The central star is a very hot white dwarf ¹. It is listed as WD 2226-210, PHL 287, and GJ 9785 ¹. It has about 0.678 times the mass of the Sun packed into about 0.025 times the Sun's radius, with a heat of 120,000 Kelvin ¹. Extra glow in mid-infrared light hints at dust tens to about one hundred times farther from the star than Earth is from the Sun, perhaps fed by many distant icy bodies ¹.