The model indicated that the disk was inclined about 30 degrees with respect to the plane of the sky around an axis with a position angle of 22 degrees.ĮSO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) has captured this unusual view of the Helix Nebula (NGC 7293), a planetary nebula located 700 light-years away. Henry confirmed O’Dell’s model and found that the Helix was a disk about 1 parsec in diameter and 0.33 parsecs in thickness. O’Dell proposed that the ring was really a thick disk. The double-ring structure appears in images taken in every band, from ultraviolet to infrared. The appearance of the Helix Nebula is recognizable across the spectrum. The Helix is not to be confused with the Double Helix Nebula, an emission nebula near the centre of the Milky Way, which has the shape of a DNA molecule seen from the side. The double-ringed structure appears like two coils on a spring. NGC 7293 is called the Helix Nebula because, from our point of view, the nebula’s gases form a pattern similar to that of a helix structure seen from the top. An earlier study determined a mass of 0.93 solar masses for the white dwarf, while more recent studies found a mass of 0.57 solar masses with an effective temperature of 120,000 K and a luminosity 76 times that of the Sun.
Henry found a mass 6.5 times that of the Sun for the progenitor star.
About 80% of known white dwarfs have hydrogen-dominated atmospheres. The central star has the stellar classification DAO.5, indicating a hydrogen-rich white dwarf. This image was created from images through blue, green and red filters and the total exposure times were 12 minutes, 9 minutes and 7 minutes respectively. A careful look at the central part of this object reveals not only the knots, but also many remote galaxies seen right through the thinly spread glowing gas. Further out from the star and beyond the ring of knots, the red colour from hydrogen and nitrogen is more prominent. The blue-green glow in the centre of the Helix comes from oxygen atoms shining under effects of the intense ultraviolet radiation of the 120 000 degree Celsius central star and the hot gas. This colour-composite image of the Helix Nebula (NGC 7293) was created from images obtained using the the Wide Field Imager (WFI), an astronomical camera attached to the 2.2-metre Max-Planck Society/ESO telescope at the La Silla observatory in Chile.
The nebula’s age is believed to be in the range between 9,400 and 12,900 years based on the measured expansion rate of 31 km/s −1. The Helix Nebula is believed to have formed about 10,600 years ago, when the central star, catalogued as GJ 9785, reached the end of its life cycle and shed its outer layers into space. The intense ultraviolet radiation from these stars causes the ejected layers of gas to glow. White dwarfs are very dense, typically packing a mass similar to that of the Sun into a volume comparable to that of the Earth. The stars become white dwarfs – hot remnant stellar cores – that energize the ejected material. Planetary nebulae like the Helix are formed when stars that are not massive enough to go out as supernovae expel their outer envelopes at the end of their evolutionary cycles. Its striking appearance has earned it the nickname the Eye of God Nebula. With an apparent magnitude of 7.6 and an apparent size of 25 arcminutes, the nebula is visible in binoculars and easily observed in small telescopes in good conditions. It is one of the closest planetary nebulae to Earth, as well as one of the brightest. The Helix Nebula (NGC 7293) is a bright, large planetary nebula located 650 light years from Earth in the constellation Aquarius.
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