Ageing Gracefully

The Helix Nebula in the Constellation Aquarius. My image taken with the Bradford Robotic Telescope on Mount Teide, Tenerife.

Planetary nebulae are the remains of stars that once looked a lot like our sun. When sun-like stars run out of their hydrogen fuel, they fuse helium instead, get hotter and puff out their outer gaseous layers. Once the helium for fusion runs out, these same layers are heated by the very hot and dense original star core.  These cores are called white dwarf stars.  Our own sun, after it leaves the main sequence, will first become a red giant star and then, some five billion years in the future, blossom into a planetary nebula. Once a star becomes a white dwarf  all nuclear fusion ceases and the star radiates its residual heat slowly to space until it finally becomes a black dwarf.  The White dwarf star starts off very very hot and consequently it is estimated that the journey from white to black dwarf  for an average star may take as long as 10 billion years.  As the Universe is 'only' some 13.7 billion years old it is unlikely that there are many if any black dwarf stars currently anywhere in the cosmos.

Image I created in APS by overlaying my image with data provided by the Spitzer Infrared Space Telescope

The intense ultraviolet radiation from the white dwarf star heats up the expelled layers of gas, which shine brightly in the infrared.  In this image: blue shows infrared light of 3.6 to 4.5 microns; green shows infrared light of 5.8 to 8 microns; and red shows infrared light of 24 microns.  The red color in the middle of the eye denotes the final layers of gas blown out when the star died. The white circle in the very center is the glow of a dusty disk circling the white dwarf star (the disc itself is too small to be resolved and is probably about the same size as the planet earth).

Credits: Bradford Robotic Telescope, NASA/JPL-Caltech and Wikipedia