The most detailed image ever obtained of the Medusa Nebula was taken using ESO’s VLT (Very Large Telescope) in Chile. It reveals in a much better way the filaments of glowing gas that make it up. Those are snake-like filaments that led to the nickname Medusa with which is commonly known, inspired by the myth of the creature with snakes in place of hair. This nebula shows what might happen to the Sun some billion years in the future.
The Medusa Nebula is scientifically known by various names and acronyms: Sharpless 2-274, Abell 21 or PN A66 2. It’s a planetary nebula, which means a nebula that is composed of ionized gases that emit electromagnetic radiation. The name was given in the 18th century by the astronomer William Herschel, who thought that they were planets in formation. Today we know that these are different phenomena but the name stuck.
Planetary nebulae can form when a star becomes a red giant and its outer layers are ejected. The ionization caused by the intense ultraviolet emitted from the star’s core make these layers of gas in turn emit electromagnetic radiation. In the case of the Medusa Nebula, the emission is very weak, also due to the fact that it’s about 1,500 light years from Earth, making it difficult to observe.
The star that originated the Medusa Nebula was perhaps similar to the Sun. Initially, after its discovery in 1955, astronomers thought that it was a nebula made of a supernova remnants. In the ’70s, thanks to the calculation of its expansion and a thermal analysis it was determined to be a planetary nebula.
The Medusa Nebula was photographed many times over the decades but the VLT allowed to obtain much greater detail. A characteristic of planetary nebulae that had initially misled astronomers was their green glow, which in the 19th century was attributed to a new element. Only in the 20th century it was determined that the color was caused by doubly ionized hydrogen([OIII]).
This study of the Medusa Nebula was made within the ESO Cosmic Gems programme, which aims to produce intriguing or visually attractive astronomical images with ESO telescopes for educational purposes or to reach the public. However, they’re also useful for scientific purposes, in this case showing better than ever a nebula that could show what will happen in a few billion years when the Sun will reach the last phase of its life becoming a red giant before shrinking into a white dwarf creating a planetary nebula.