The Medusa Nebula is a large planetary nebula, about 4 light years across, in the constellation of Gemini on the Canis Minor border. It also known as Abell 21 and Sharpless 2-274 and was originally discovered in 1955 by UCLA astronomer
George O. Abell. The braided serpentine filaments of glowing gas suggests the serpent hair of Medusa found in ancient Greek mythology. Until the early 1970s, the Medusa was thought to be a supernova remnant. With the computation of expansion velocities and the thermal character of the radio emission, Soviet astronomers in 1971 concluded that it was most likely a planetary nebula.
Planetary nebulas are characterized by a particular form of glowing gas called doubly ionized oxygen. The gas is excited by ultraviolet radiation emanating from the star, which strips away electrons from the gas. The colourful display of gas some 1,500 light-years from Earth is happening because a star in the center of the nebula is shedding its outer layers into space. The gas will persist for a few tens of thousands of years until it moves away, leaving behind a cold remnant of the star, called a white dwarf. This is a common fate for stars that are about the size of our sun. The ejection of mass from stars at this stage of their evolution is often intermittent, which can result in fascinating structures within planetary nebulae. 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. Astronomers using ESO’s Very Large Telescope in Chile have captured the most detailed image ever taken of the Medusa Nebula.
Credits: AIS, ESO, NASA, Wikipedia.