These images of planetary nebulae in infrared light were released by NASA's Spitzer Space Telescope in time for Halloween. Planetary nebulae represent the last stages of evolution for Sun-like stars, where their ejected outer layers are lit up by ultraviolet light from the remnants of the central star. The name ‘planetary nebula’ is a bit of a misnomer, as when they were first observed their apparent disk-like structure and similarity to Uranus and Neptune led them to be linked with planets.
All low- and intermediate-mass stars like our Sun will suffer a similar fate. Depending on the mass of the star, it will run out of fuel millions to billions of years after it formed. After its supply of hydrogen in the core is gone, the nuclear fusion there ceases and puff up into giant red stars called ‘red giants’. The red giants eventually eject their outer layers which then expand away from the star. The ultraviolet light from the core of the star energises the ejected layers, causing the floating material to glow and accentuate the shape.
Exposed Cranium Nebula (left image)
More formally known as PMR 1, this planetary nebula is located around 5,000 light-years away in the Vela constellation. Within the nebula is a hot, massive dying star that is rapidly losing its mass. The nebula’s insides appear red in this image and mainly consist of ionised gas. The outer green shell is cooler and is composed of glowing hydrogen molecules.
Ghost of Jupiter Nebula (middle image)
This planetary nebula, also known as NGC 3242, can be found around 1,400 light-years away in the constellation Hydra. The infrared image demonstrates the cooler outer halo of the dying star, which is coloured in red. Concentric rings can be seen around the object, the result of material being ejected every now and then during the star's death.
Little Dumbbell Nebula (right image)
Also known as NGC 650, this planetary nebula is about 2,500 light-years from Earth in the Perseus constellation. NGC 650 has a butterfly or bipolar shape due to its disk of thick material that runs from the lower left to the upper right. Fast winds are blowing material away from the star and the green and red clouds are from the glowing hydrogen molecules within. The green area is hotter than the red.
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