Not all nebulas are built alike. Some emit no light at all, appearing as dark streaks across the cosmos. Some reflect the light of nearby stars. Others emit their own light in optical wavelengths. This last kind -- emission nebulas -- is magnificent to behold, as evidenced by the Prawn Nebula (aka IC4628 or Gum 56). A high-resolution image of the nebula was released Wednesday by the European Southern Observatory in Chile.
While perhaps the most famous emission nebula is the Orion Nebula, the Prawn Nebula has a lot going for it too. It's a stellar nursery, which means it contains a lot of very hot, bright, young stars.
Two of these stars are rare O-type stars, very large and very hot, glowing blue-white. They're also known as blue giants, and they're very short lived. Because they're so large and hot, they tend to burn out quickly, ending their brief lives in intense supernovas before collapsing into black holes or neutron stars.
These two blue giants are what makes the gas of the Prawn Nebula glow, with some help from the other young stars. They give off enormous amounts of ultraviolet radiation, which breaks down the nebula's hydrogen gas into the component nuclei and electrons in a process called ionisation.
When the nuclei and electrons recombine, they have much higher energy levels that before, which gets released in the form of light, causing the nebula to glow.
The Prawn Nebula is huge, coming in at around 250 light-years in diameter. It's also very active. As well as fostering the two blue giants and other very young stars, it is also still in the process of stellar formation, where dust and gas collapse into a core to form the very early stages of a baby star.
Regions in which stellar formation is still taking place are visible in the new image as particularly dense clouds. These are created when stars go supernova, leaving behind clouds of dust and gas, which then go on to perpetuate the cycle of stellar life.
If you're in the southern hemisphere and have a powerful telescope, point it in the direction of the constellation Scorpius. The Prawn Nebula is some 6,000 light-years distant, and is projected to cover a region of sky around four times the size of the full moon. Keep in mind, it's very faint, and can't be spotted with a smaller telescope.