The Helix Nebula (also known as NGC 7293 or Caldwell 63 ) is a planetary nebula (PN) located in the constellation Aquarius . Discovered by Karl Ludwig Harding , most likely before 1824, this object is one of the closest of all the bright planetary nebulae to Earth. The distance, measured by the Gaia mission, is 655±13 light-years. It is similar in appearance to the Cat's Eye Nebula and the Ring Nebula , whose size, age, and physical characteristics are similar to the Dumbbell Nebula , varying only in its relative proximity and the appearance from the equatorial viewing angle. The Helix Nebula has sometimes been referred to as the "Eye of God" in pop culture , as well as the " Eye of Sauron ".
18-513: C63 or C-63 may refer to: Caldwell 63 , a planetary nebula Convention concerning Statistics of Wages and Hours of Work, 1938 of the International Labour Organization JNR Class C63 , a proposed Japanese steam locomotive Lockheed C-63 Hudson , an American military transport aircraft Mercedes-AMG C 63 , a German automobile Ruy Lopez ,
36-504: A chess opening [REDACTED] Topics referred to by the same term This disambiguation page lists articles associated with the same title formed as a letter–number combination. If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=C63&oldid=1224126978 " Category : Letter–number combination disambiguation pages Hidden categories: Short description
54-523: A cometary knot located in the inner region of the nebula are about 2.5'(arcmin) from the CS, and is calculated at about 900 K in the outer region at the distance of 5.6'. The central star of the Helix Nebula is a white dwarf of spectral type DAO. It has the designations WD 2226-210, PHL 287, and GJ 9785. The star has a radius of 0.025 solar radii (17,000 km), a mass of 0.678 M ☉ ,
72-573: A core of neutral molecular gas and containing bright local photoionization fronts or cusps towards the central star and tails away from it. All tails extend away from the Planetary Nebula Nucleus (PNN) in a radial direction. Excluding the tails, each knot is approximately the size of the Solar System , while each of the cusp knots are optically thick due to Lyc photons from the CS. There are about 40,000 cometary knots in
90-722: A ground-state molecule and the target ion. This can be initialized by computing the vibrations of a molecule and associated cation (post ionization) using quantum chemical software e.g. QChem. For photon energies below the ionization threshold, the photoionization cross-section is near zero. But with the development of pulsed lasers it has become possible to create extremely intense, coherent light where multi-photon ionization may occur via sequences of excitations and relaxations. At even higher intensities (around 10 – 10 W/cm of infrared or visible light), non-perturbative phenomena such as barrier suppression ionization and rescattering ionization are observed. Several photons of energy below
108-402: A radius of 0.021 solar radii (15,000 km), or about 2.3 times the radius of Earth . Photoionization Photoionization is the physical process in which an ion is formed from the interaction of a photon with an atom or molecule . Not every interaction between a photon and an atom, or molecule, will result in photoionization. The probability of photoionization is related to
126-406: A temperature of 120,000 Kelvin and has an apparent magnitude of 13.5. A 2024 study hypothesized that the central star might be orbited by a planet based on periodic variations in its light curve , but it cannot be ruled out that these variations are due to intrinstic stellar variability. Assuming an inclination of 25° (aligned with the nebula itself), this hypothetical planet is estimated to have
144-423: Is different from Wikidata All article disambiguation pages All disambiguation pages Caldwell 63 The Helix Nebula is an example of a planetary nebula, formed by an intermediate to low-mass star, which sheds its outer layers near the end of its evolution. Gases from the star in the surrounding space appear, from Earth's perspective, a helix structure. The remnant central stellar core, known as
162-451: The photoionization cross section of the species – the probability of an ionization event conceptualized as a hypothetical cross-sectional area. This cross section depends on the energy of the photon (proportional to its wavenumber) and the species being considered i.e. it depends on the structure of the molecular species. In the case of molecules, the photoionization cross-section can be estimated by examination of Franck-Condon factors between
180-557: The Helix Nebula. The knots are probably the result of Rayleigh-Taylor instability . The low density, high expansion velocity ionized inner nebula is accelerating the denser, slowly expanding, largely neutral material which had been shed earlier when the star was on the Asymptotic Giant Branch . The excitation temperature varies across the Helix nebula. The rotational-vibrational temperature ranges from 1800 K in
198-424: The atom. The excess energy gives the released electron higher kinetic energy than the usual case of just-above threshold ionization. More precisely, the system will have multiple peaks in its photoelectron spectrum which are separated by the photon energies, indicating that the emitted electron has more kinetic energy than in the normal (lowest possible number of photons) ionization case. The electrons released from
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#1732797519619216-422: The central star (CS) of the planetary nebula, is destined to become a white dwarf star. The observed glow of the central star is so energetic that it causes the previously expelled gases to brightly fluoresce . The nebula is in the constellation of Aquarius , and lies about 650 light-years away, spanning about 0.8 parsecs (2.5 light-years). Its age is estimated to be 10 600 +2300 −1200 years, based on
234-573: The inner disk. The Helix Nebula was the first planetary nebula discovered to contain cometary knots . Its main ring contains knots of nebulosity, which have now been detected in several nearby planetary nebulae, especially those with a molecular envelope like the Ring nebula and the Dumbbell Nebula . These knots are radially symmetric (from the CS) and are described as "cometary", each centered on
252-457: The ionization threshold may actually combine their energies to ionize an atom. This probability decreases rapidly with the number of photons required, but the development of very intense, pulsed lasers still makes it possible. In the perturbative regime (below about 10 W/cm at optical frequencies), the probability of absorbing N photons depends on the laser-light intensity I as I . For higher intensities, this dependence becomes invalid due to
270-422: The outer-most ring is about 25 arcmin in diameter (1.76 pc). The outer-most ring appears flattened on one side due to it colliding with the ambient interstellar medium . Expansion of the whole planetary nebula structure is estimated to have occurred in the last 6,560 years, and 12,100 years for the inner disk. Spectroscopically, the outer ring's expansion rate is 40 km/s, and about 32 km/s for
288-429: The ratio of its size to its measured expansion rate of 31 km·s . The Helix Nebula is thought to be shaped like a prolate spheroid with strong density concentrations toward the filled disk along the equatorial plane, whose major axis is inclined about 21° to 37° from our vantage point. The size of the inner disk is 8×19 arcmin in diameter (0.52 pc); the outer torus is 12×22 arcmin in diameter (0.77 pc); and
306-418: The target will have approximately an integer number of photon-energies more kinetic energy. When either the laser intensity is further increased or a longer wavelength is applied as compared with the regime in which multi-photon ionization takes place, a quasi-stationary approach can be used and results in the distortion of the atomic potential in such a way that only a relatively low and narrow barrier between
324-414: The then occurring AC Stark effect . Resonance-enhanced multiphoton ionization (REMPI) is a technique applied to the spectroscopy of atoms and small molecules in which a tunable laser can be used to access an excited intermediate state . Above-threshold ionization (ATI) is an extension of multi-photon ionization where even more photons are absorbed than actually would be necessary to ionize
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