A Ghostly Green Bubble
ESO’s VLT snaps a planetary nebula
10 April 2013
This intriguing new picture from ESO’s Very Large Telescope shows the glowing green planetary nebula IC 1295 surrounding a dim and dying star located about 3300 light-years away in the constellation of Scutum (The Shield). This is the most detailed picture of this object ever taken.
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 colourful glowing clouds of ionised gas known as planetary nebulae.
This new image from the VLT shows the planetary nebula IC 1295, which lies in the constellation of Scutum (The Shield). 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 colours and the ghostly green shade that is prominent in IC 1295 comes from ionised oxygen.
At the centre 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 very faint white dwarf and slowly cool down over many billions of years.
Stars with masses like the Sun and up to eight times that of the Sun, will form planetary nebulae as they enter the final phase of their existence. The Sun is 4.6 billion years old and it will likely live another four 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 nineteenth 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 (coloured blue), visible light (coloured green), and red light (coloured red) have been combined to make this picture.
 Even early observers such as William Herschel, who discovered many planetary nebulae and speculated about their origin and composition, knew that they weren’t actually planets orbiting the Sun as they did not move relative to the surrounding stars.
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.