Anne’s Picture of the Day: Protoplanetary Nebula IRAS 20068+4051

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December 22, 2012

IRAS 20068+4051, a protoplanetary nebula in Cygnus

Image Credit: ESA/Hubble & NASA

IRAS 20068+4051 is a bipolar protoplanetary nebula of about 13 light-years in length, located some 18,000 light-years away in the constellation of Cygnus (The Swan).

Despite their name, protoplanetary nebulae have nothing to do with planets. The name of planetary nebulae arose because of the visual similarity between some round planetary nebulae and the planets Uranus and Neptune when viewed through early telescopes.

Protoplanetary nebulae are clouds of dust and gas formed from material shed by an aging central star similar in mass to our Sun. For such a star death is a long process. After billions of years, the hydrogen fuel that powers the star begins to run out. The star balloons to great size and becomes a red giant. Eventually, however, the star collapses back on itself. This increases the temperature at its core and most of the stars material is catapulted into space, enveloping itself in clouds of gas, but the core is not yet hot enough to make the gas itself glow on its own. Instead, the gas is merely reflecting the light from the star.

But as the star continues to evolve, it becomes hot enough to emit strong ultraviolet light. At that point it will have the power needed to make the gas glow, and will become a real full-fledged planetary nebula. But before the nebula begins to shine, fierce winds of material ejected from the star will continue to shape the surrounding gas into intricate patterns. Then the star cools down and all that is left after this process is the exposed, hot and dead core, known as a white dwarf.

A protoplanetary nebula is a relatively short-lived phenomenon, so finding one is a rare opportunity for astronomers to learn more about them and to observe the beginning of the formation of planetary nebulae (hence the name protoplanetary, or preplanetary nebulae).

IRAS 20068+4051 is such a strange cloud of gas and dust that envelops a star at a late stage in its life. Its dusty wings, resembling a butterfly, formed when its progenitor star exhausted its hydrogen fuel for nuclear fusion, causing the outer layers of the star to expand and cool, creating a huge, surrounding envelope of dust and gas around the star. Its structure was once spherical, but powerful stellar winds have twisted it into the butterfly shape we see now.
Meanwhile, as the central star continues to evolve, finding new ways to prevent itself from collapsing under its own gravity, it will eventually become hot enough to make the gas glow as a spectacular planetary nebula. These objects emit a broad spectrum of radiation, including visible light, making them great targets for both amateur and professional astronomers.

However, protoplanetary nebulae, which often appear smaller and are seen best in infrared light, are much trickier to observe, particularly since water vapour in the Earth’s atmosphere absorbs most infrared wavelengths. But Hubble has exceptionally sharp vision and an unobstructed vantage point in space, making it possible to capture stunning images of peculiar objects like IRAS 20068+4051.

This image was created from pictures taken through yellow (coloured blue in this photo) and near-infrared (coloured red) filters using the High Resolution Channel of Hubble’s Advanced Camera for Surveys.

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