Astronomers using ESO’s Very Large Telescope (VLT) in Chile have managed to obtain the most detailed image ever taken of the Medusa Nebula.
This image uses data from the FORS instrument on the Very Large Telescope. The stellar core of the Medusa Nebula is not the bright star in the center of this image – this is a foreground star called TYC 776-1339-1. Medusa’s central star is a dimmer, bluish star lying just off-center of the crescent shape and in the right-hand part of this image. Image credit: ESO.
The Medusa Nebula, also known as Sharpless 2-274, Abell 21 or PN A66 21, is a nebula approximately 800 light-years away in the constellation Gemini.
It was discovered in 1955 by the American astronomer George Abell, who classified it as an old planetary nebula.
The nebula represents a final stage in the evolution of low mass stars like our Sun and is estimated to be over 4 light-years across.
For some time astronomers debated whether the object could be the remnant of a supernova explosion. In the 1970s, however, they were able to measure the movement and other properties of the material in it and clearly identify it as a planetary nebula.
The nebula’s mythological namesake, Medusa Gorgon, was a hideous creature with snakes in place of hair.
These snakes are represented by the serpentine filaments of glowing gas in the Medusa Nebula. The red glow from hydrogen and the fainter green emission from oxygen gas extends well beyond this frame, forming a crescent shape in the sky. The ejection of mass from stars at this stage of their evolution is often intermittent, which can result in fascinating structures within planetary nebulae.
Harsh UV radiation from the very hot star at the core of the nebula causes atoms in the outward-moving gas to lose their electrons, leaving behind ionized gas. The characteristic colors of this glowing gas can be used to identify objects.
In particular, the presence of the green glow from doubly ionized oxygen is used as a tool for spotting planetary nebulae.
By applying appropriate filters, astronomers can isolate the radiation from the glowing gas and make the dim nebulae appear more pronounced against a darker background.
When the green emission from nebulae was first observed, astronomers thought they had discovered a new element that they named nebulium. They later realized that it was simply a rare wavelength of radiation from an ionized form of the familiar element oxygen.
