Anne’s Picture of the Day: Planetary Nebula Fleming 1

January 17, 2013

Fleming 1, a planetary nebula in Centaurus

Fleming 1, a planetary nebula in Centaurus

Image Credit: ESO/H. Boffin

Fleming 1 is a planetary nebula that lies about 10,000 light-years away in the constellation of Centaurus, while moving away from us at approximately 28.6 kilometers per second. It is named after the Scottish astronomer Williamina Fleming, who discovered the nebula in 1910.

Despite their name, planetary 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.

When a star with a mass up to eight times that of the Sun runs out of fuel at the end of its life, it blows off its outer shells and begins to lose mass. This allows the hot, inner core of the star (collapsing from a red giant to a white dwarf) to radiate strongly, causing this outward-moving cocoon of gas to glow brightly as a planetary nebula.

Over the next several thousand years, the nebula will gradually disperse into space, and then the star will cool and fade away for billions of years as a white dwarf. Our own Sun is expected to undergo a similar fate, but fortunately this will not occur until some 5 billion years from now.

In the case of Fleming 1, it is likely that not one but two white dwarfs lie at the heart of the nebula, circling each other every 1.2 days. Although binary stars have been found at the hearts of planetary nebulae before, systems with two white dwarfs orbiting each other are very rare.

It is also found that Fleming 1 has a knotted ring of material within the inner nebula. Such a ring of material is also known to exist in other binary systems, and appears to be a tell-tale signature of the presence of a stellar couple.

However, their orbital motions can fully explain the remarkably symmetric structures of the jets in this and similar objects.

The jets of Fleming 1 appear to shoot from both poles of the central region in S-shaped flows. These patterns, that weave into knotty, curved patterns in the surrounding gas clouds, are the result of the close interaction between the binary white dwarf stars.

As the stars aged, they expanded, and sometimes one star became a stellar vampire, sucking matter from its twin. That matter was drawn towards the vampire and accreted around it in a disk. As the two stars circle each other, they cause the disk to wobble like a spinning top.

That movement forces matter outward at the poles of the system – the jets. Such a wobbling disk of gaseous matter in binary star systems is the cause of the remarkably symmetrical shapes appearing around planetary nebulae like Fleming 1.

This image is taken with ESO’s Very Large Telescope.

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