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Fireworks display in the
Helix Nebula

DR EMILY BALDWIN
ASTRONOMY NOW

Posted: JULY 7, 2009


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A new image taken by the Subaru Telescope shows tens of thousands of previously unseen comet-shaped knots lighting up the Helix Nebula like a spectacular fireworks display frozen in time.

Optical image of the Helix Nebula showing diffuse gas around a central star. Image: NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner [STScI], and T.A. Rector [NRAO]

The Helix Nebula, NGC 7293, is located just 710 light years from Earth and was the first planetary nebula in which knots were observed. Planetary nebula represent the final stages in the lives of low-mass stars, like our Sun, as they throw off shells of gaseous material into space. Although planetary nebulae can look like explosive fireworks displays, the process takes between some 10,000 to 1,000,000 years.

New near-infrared image of the Helix Nebula, showing comet-shaped knots within. These features look like a fireworks display in space. Image: Subaru Telescope.

An international team of astronomers used the Subaru telescope in Hawaii to study the hydrogen molecule emission of the nebula in the infrared, and discovered knots of material throughout the entire nebula. Usually these molecules are destroyed by the ultraviolet radiation in space, but in this case have been protected by the knots of gas and dust observed in optical images. The comet-like shape of these objects result from the steady evaporation of gas from the knots, produced by strong winds and ultraviolet radiation from the dying star in the heart of the nebula.

"This research shows how the central star slowly destroys the knots and highlights the places where molecular and atomic material can be found in space," says lead astronomer Mikako Matsuura, previously at the National Astronomical Observatory of Japan and now at University College London.

Enlarged image, showing an enormous number of knots. The size of each knot is about five times as big as Pluto's orbit in the Solar System. Image: Subaru Telescope.

Enlarged image, showing cometary shaped knots. Knots have gradually formed from material ejected from stars in the past, which are now exposed to ultraviolet radiation and wind from the central star. Image: Subaru Telescope.

The infrared images show the knots extending out to greater distances than previously observed, with the extent of the 'tails' varying with the distance from the central star, mimicking the behaviour of Solar System comets which have larger tails when they are closer to the Sun and when wind and radiation is stronger.

The astronomers suggest there may be as many as 40,000 knots in the nebula, each of which are billions of kilometers across and amounting to a combined mass of 30,000 Earths. The origin of the knots – whether remnants of the star's planetary system or material ejected from the star itself – is currently unknown, but either way, will shed light on the lives of stars and planetary systems.

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