IRAS 13208-6020, a protoplanetary nebula in Centaur

IRAS 13208-6020, a protoplanetary nebula in Centaur

Image Credit: ESA/Hubble & NASA

IRAS 13208-6020 is a bipolar protoplanetary nebula in the constellation Centaur, formed from material that is shed by a dying central star. The nebula has two very similar outflows of material in opposite directions and a clearly visible dusty ring surrounding the central star.

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. Then the core shrinks and heats up. At the same time the star ejects its cooler outer layers, 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 that can only be truly appreciated later once the nebula begins to glow. 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).

Despite their name, planetary nebulae and (thus) 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.

Although there are lots of (proto)planetary nebulae shaped like IRAS 13208-6020, with twin outflows of material resembling a butterfly, its shape is really strange. A star all alone in space would normally emit gas in a rough sphere around itself, but in this case something is shaping the wind. Most likely it’s some sort of companion: a star orbiting very close in, perhaps. Or, it’s possible that the central star had planets, and as it was dying it expanded, engulfing those planets. As they orbited inside the star, frying the whole time, they would help accelerate the star’s spin. That too could produce the bipolar shape of the gas around the star.

This picture was created from images taken with the NASA/ESA Hubble Space Telescope, using the High Resolution Channel of Hubble’s Advanced Camera for Surveys. Images taken in visible light and in infrared light have been combined to create this picture.

Usually, (proto)planetary nebulae are faint in the infrared, but this one is quite bright in that light; the gas itself doesn’t emit much infrared light, but the star sure does, and the gas is reflecting it.

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