Stars the size of the Sun end their lives as tiny and faint white dwarf stars. But as they make the final transition into retirement, their atmospheres are blown away into space. For a few tens of thousands of years, they are surrounded by the spectacular and colorful glowing clouds of ionized gas known as planetary nebulae.
This new image from the VLT shows the planetary nebula IC 1295. It has the unusual feature of being surrounded by multiple shells that make it resemble a micro-organism seen under a microscope, with many layers corresponding to the membranes of a cell.
These bubbles are made out of gas that used to be the star’s atmosphere. This gas has been expelled by unstable fusion reactions in the star’s core that generated sudden releases of energy, like huge thermonuclear belches. The gas is bathed in strong ultraviolet radiation from the aging star, which makes the gas glow. Different chemical elements glow with different colors, and the ghostly green shade that is prominent in IC 1295 comes from ionized oxygen.
At the center of the image, you can see the burnt-out remnant of the star’s core as a bright blue-white spot at the heart of the nebula. The central star will become a faint white dwarf and slowly cool down over billions of years.
Stars with masses like the Sun and up to 8 solar masses will form planetary nebulae as they enter the final phase of their existence. The Sun is 4.6 billion years old, and it likely will live another 4–5 billion years.
Despite the name, planetary nebulae have nothing to do with planets. This descriptive term was applied to some early discoveries because of the visual similarity of these unusual objects to the outer planets Uranus and Neptune, when viewed through early telescopes, and it has been catchy enough to survive. These objects were shown to be glowing gas by early spectroscopic observations in the 19th century.
This image was captured by ESO’s Very Large Telescope, located on Cerro Paranal in the Atacama Desert of northern Chile, using the FORS instrument (FOcal Reducer Spectrograph). Exposures taken through three different filters that passed blue light (colored blue), visible light (colored green), and red light (colored red) have been combined to make this picture.