![]() These velocities indicate a spatial expansion velocity of the inner disk of 40 and 32 km s -1 for the outer ring, which yields expansion ages of 6560 and 12,100 yr, respectively. Published radial velocities of the knots provide support for the two-component structure of the main ring of the nebula and for the idea that the knots found there are expanding along with the nebular material from which they recently originated. The inner disk has an extended distribution of low-density gas along its rotational axis of symmetry, and the disk is optically thick to ionizing radiation, as is the outer ring. This outer ring is surrounded by an outermost ring of 1500" (1.76 pc) diameter, which is flattened on the side colliding with the ambient interstellar medium. ![]() These images have allowed us to determine that the main ring of the nebula is composed of an inner disk of about 499" diameter (0.52 pc) surrounded by an outer ring (in reality a torus) of 742" diameter (0.77 pc) whose plane is highly inclined to the plane of the disk. It is currently unclear how the cometary knots may have originated.Through Hubble Space Telescope (HST) imaging of the inner part of the main ring of the Helix Nebula, together with CTIO 4 m images of the fainter outer parts, we have a view of unprecedented quality of the nearest bright planetary nebula. 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 dust and molecular gas. The material clumps into filaments that radiate out from the centre and the whole view resembles a celestial firework display.Įven though they look tiny, these strands of molecular hydrogen, known as cometary knots, are about the size of our Solar System. The infrared light picks out how the cooler, molecular gas is organised. The powerful vision of ESO's VISTA telescope also reveals fine structure in the nebula's rings. The 4.1-metre telescope is also able to detect an impressive array of background stars and galaxies. 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. ![]() This is particularly clear in this infrared view since red molecular gas can be seen across much of the image. However, material from the nebula spreads out from the star to at least four light-years. The main ring of the Helix is about two light-years across, roughly half the distance between the Sun and the nearest star. Acknowledgment: Cambridge Astronomical Survey Unit The infrared vision of VISTA reveals strands of cold nebular gas that are mostly obscured in visible light images of the Helix. ![]() This video compares a new view of the Helix Nebula acquired with the VISTA telescope in infrared light with the more familiar view in visible light from the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory. The nebula itself is a complex object composed of dust, ionised 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 hot star. It is evolving to become a white dwarf star and appears as the tiny blue dot seen at the centre of the image. Unable to hold onto its outer layers, the star slowly shed shells of gas that became the nebula. This strange object formed when a star like the Sun was in the final stages of its life. It lies in the constellation of Aquarius (The Water Bearer), about 700 light-years away from Earth. The Helix Nebula is one of the closest and most remarkable examples of a planetary nebula.
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