science & techESA/Hubble
A dying Sun-like star's glowing shell is far richer in nitrogen and neon than the Sun
NGC 6153 is a planetary nebula about 4,000 light-years away, the glowing shell a Sun-like star throws off at the end of its life. Ultraviolet light from the hot core ionises the ejected gas, which makes it glow. Measurements show the nebula holds neon, argon, oxygen, carbon and chlorine up to three times the levels found in the Solar System, and five times the Sun's nitrogen. The likeliest explanation is that the star formed from a cloud already rich in these elements rather than making them itself, which tells astronomers about the chemistry of the region where it was born.
A Sun-like star sheds its outer layers in slow winds late in life. Its exposed hot core emits intense ultraviolet light, which strips electrons from the gas and makes it fluoresce. The shell thins over tens of thousands of years while the core cools into a white dwarf.
Elements heavier than hydrogen and helium are forged in stars and returned to space, so the chemistry of a nebula records the gas it formed from. Measuring clouds like this helps astronomers trace how galaxies have enriched themselves over billions of years.
Planetary nebulae have nothing to do with planets; 18th-century astronomers named them because through small telescopes they looked like round planetary discs.
