These two images, taken by the European Southern Observatory’s La Silla Observatory in Chile, show a peculiar cloud of gas 800 light years away in the Vela constellation known as the Pencil Nebula (NGC 2736).
The Pencil Nebula is a cloud of glowing gas left behind after a supernova explosion 11,000 years ago. It is only a portion of the entire supernova remnant, but it is the brightest region. The peculiar shape of this cosmic structure has earned it the moniker of the ‘Witch’s Broom’ as the glowing filaments resemble the strands on a broom.
The whole remnant is known as the Vela supernova remnant, a giant expanding shell of gas from the initial explosion that moved at millions of kilometres per hour when it first formed. Having moved through the gas between stars, the expanding shell is now slowing down with certain regions of it glowing brighter than others, such as the Pencil Nebula imaged here.
The brightest regions of the Pencil Nebula are areas where the supernova’s shock waves have hit dense regions of interstellar gas, at one point heating the gas to millions of degrees. The gas is now cooling down but it continues to give off a faint glow. The blue areas of the nebula are the hottest, full of ionised oxygen atoms, whereas the red regions are cooler and emit hydrogen.
The Pencil Nebula is 0.75 light years across and expanding at a ‘leisurely’ 650,000 kilometres per hour (400,000 miles per hour), about 0.06% the speed of light. Such is the rate of its expansion that within a human generation it will move to a different position in the night sky.
Image Credit: ESO