by Staff Writers
Garching, Germany (SPX) Jan 23, 2012
ESO's VISTA telescope, at the Paranal Observatory in Chile, has captured a striking new image of the Helix Nebula. This picture, taken in infrared light, reveals strands of cold nebular gas that are invisible in images taken in visible light, as well as bringing to light a rich background of stars and galaxies.
The Helix Nebula is one of the closest and most remarkable examples of a planetary nebula. It lies in the constellation of Aquarius (The Water Bearer), about 700 light-years away from Earth.
This strange object formed when a star like the Sun was in the final stages of its life. Unable to hold onto its outer layers, the star slowly shed shells of gas that became the nebula, before becoming a white dwarf, the tiny blue dot seen at the center of the image.
The nebula itself is a complex object composed of dust, ionized material as well as molecular gas, arrayed in a beautiful and intricate flower-like pattern and glowing in the fierce glare of ultraviolet light from the central white dwarf star.
The main ring of the Helix is about two light-years across, roughly half the distance between the Sun and the nearest star. However, material from the nebula spreads out from the star to at least four light-years. This is particularly clear in this infrared view since red molecular gas can be seen across much of the image.
While hard to see visually, the glow from the thinly spread gas is easily captured by VISTA's special detectors, which are very sensitive to infrared light. The 4.1-meter telescope is also able to detect an impressive array of background stars and galaxies.
The powerful vision of ESO's VISTA telescope also reveals fine structure in the nebula's rings. The infrared light can penetrate the obscuring dust and the hotter, ionized gas to show how the cooler, molecular gas is organized. The material clumps into filaments that radiate out from the center and the whole view resembles a celestial firework display.
Even though they look tiny, these strands of molecular hydrogen, known as cometary knots, are about the size of our Solar System. The molecules in them are able to survive the high-energy radiation that emanates from the dying star precisely because they clump into these knots, which in turn are shielded by the dust and ionized gas seen in optical images. It is currently unclear how the cometary knots may have originated.
 Planetary nebulae have nothing to do with planets. This confusing name arose because many of them show small bright discs when observed visually and resemble the outer planets in the Solar System, such as Uranus and Neptune. The Helix Nebula, which also bears the catalogue number NGC 7293, is unusual as it appears very large, but also very faint, when viewed through a small telescope.
Stellar Chemistry, The Universe And All Within It
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