NGC 7027
Encyclopedia
NGC 7027 is a very young and dense planetary nebula
located around 3000 ly away in the constellation
Cygnus
. It was discovered in 1878 by Édouard Jean-Marie Stephan
, using the 31 inch reflector at Marseille Observatory
. It is one of the smallest planetary nebulae, and by far the most extensively studied.
NGC 7027 is one of the visually brightest planetary nebulae. It is about 600 years old.
It is unusually small, measuring only 0.2 by 0.1 light-years whereas the typical size for a planetary nebula is 1 light-year. It has a very complex shape, consisting of an elliptical region of ionized gas within a massive neutral cloud. The inner structure is surrounded by a translucent shroud of gas and dust.
The nebula is shaped like a prolate ellipsoidal shell and contains a photodissociation
region shaped like a "clover leaf". NGC 7027 is expanding at 17 km/s. The central regions of NGC 7027 have been found to emit X-ray
s, indicating very high temperatures. Surrounding the ellipsoidal nebula are a series of faint, blue concentric shells.
It is possible that the central white dwarf
of NGC 7027 has an accretion disk that acts as a source of high temperatures. The white dwarf is believed to have a mass approximately 0.7 times the mass of the Sun and is radiating at 7,700 times the Sun's luminosity
. NGC 7027 is currently in a short phase of planetary nebula evolution in which molecules in its envelope are being dissociated into their component atoms, and the atoms are being ionized.
The expanding halo of NGC 7027 has a mass of about three times the mass of the Sun
, and is about 100 times more massive than the ionized central region. This mass loss in NGC 7027 provided important evidence that stars a few times more massive than the Sun can avoid being destroyed in supernova
explosions.
NGC 7027 has a rich and highly ionized spectrum
caused by its hot central star. The nebula is rich in carbon
, and is a very interesting object for the study of carbon chemistry in dense molecular material exposed to strong ultraviolet
radiation. The spectrum of NGC 7027 contains fewer spectral lines from neutral molecule
s than is usual for planetary nebulae. This is due to the destruction of neutral molecules by intense UV radiation. The nebula contains ions of extremely high ionization potential
. NGC 7027 is a promising place to look for HeH+, a molecule which is believed to exist in interstellar space, but which has never been conclusively identified. There is evidence for the presence of nanodiamond in NGC 7027.
It was photographed by the Hubble Space Telescope
in 1996. Prior to these observations, NGC 7027 was thought to be a proto-planetary nebula with the central star too cool to ionize any of the gas, but it is now known to be a planetary nebula in the earliest stage of its development. The central star is believed to have been about 3–4 times the mass of the Sun.
Despite being so well known and studied, NGC 7027 does not have a popular name. In a 6" telescope at around 50x it appears as a relatively bright bluish star. It is best viewed with the highest magnification possible.
Planetary nebula
A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
located around 3000 ly away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Cygnus
Cygnus (constellation)
Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...
. It was discovered in 1878 by Édouard Jean-Marie Stephan
Édouard Jean-Marie Stephan
Édouard Jean-Marie Stephan was a French astronomer. His surname is sometimes spelled Stéphan in some literature, but this is apparently erroneous....
, using the 31 inch reflector at Marseille Observatory
Marseille Observatory
Marseille Observatory or Observatoire de Marseille is an astronomical observatory run by the University of Provence. It is located near Marseille, France. In its first incarnation, it was the discovery site of a group of galaxies known as Stephan's Quintet or Hickson 92, discovered by Édouard...
. It is one of the smallest planetary nebulae, and by far the most extensively studied.
NGC 7027 is one of the visually brightest planetary nebulae. It is about 600 years old.
It is unusually small, measuring only 0.2 by 0.1 light-years whereas the typical size for a planetary nebula is 1 light-year. It has a very complex shape, consisting of an elliptical region of ionized gas within a massive neutral cloud. The inner structure is surrounded by a translucent shroud of gas and dust.
The nebula is shaped like a prolate ellipsoidal shell and contains a photodissociation
Photodissociation
Photodissociation, photolysis, or photodecomposition is a chemical reaction in which a chemical compound is broken down by photons. It is defined as the interaction of one or more photons with one target molecule....
region shaped like a "clover leaf". NGC 7027 is expanding at 17 km/s. The central regions of NGC 7027 have been found to emit X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s, indicating very high temperatures. Surrounding the ellipsoidal nebula are a series of faint, blue concentric shells.
It is possible that the central white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
of NGC 7027 has an accretion disk that acts as a source of high temperatures. The white dwarf is believed to have a mass approximately 0.7 times the mass of the Sun and is radiating at 7,700 times the Sun's luminosity
Luminosity
Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...
. NGC 7027 is currently in a short phase of planetary nebula evolution in which molecules in its envelope are being dissociated into their component atoms, and the atoms are being ionized.
The expanding halo of NGC 7027 has a mass of about three times the mass of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, and is about 100 times more massive than the ionized central region. This mass loss in NGC 7027 provided important evidence that stars a few times more massive than the Sun can avoid being destroyed in supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
explosions.
NGC 7027 has a rich and highly ionized spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
caused by its hot central star. The nebula is rich in carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, and is a very interesting object for the study of carbon chemistry in dense molecular material exposed to strong ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
radiation. The spectrum of NGC 7027 contains fewer spectral lines from neutral molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s than is usual for planetary nebulae. This is due to the destruction of neutral molecules by intense UV radiation. The nebula contains ions of extremely high ionization potential
Ionization potential
The ionization energy of a chemical species, i.e. an atom or molecule, is the energy required to remove an electron from the species to a practically infinite distance. Large atoms or molecules have a low ionization energy, while small molecules tend to have higher ionization energies.The property...
. NGC 7027 is a promising place to look for HeH+, a molecule which is believed to exist in interstellar space, but which has never been conclusively identified. There is evidence for the presence of nanodiamond in NGC 7027.
It was photographed by the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
in 1996. Prior to these observations, NGC 7027 was thought to be a proto-planetary nebula with the central star too cool to ionize any of the gas, but it is now known to be a planetary nebula in the earliest stage of its development. The central star is believed to have been about 3–4 times the mass of the Sun.
Despite being so well known and studied, NGC 7027 does not have a popular name. In a 6" telescope at around 50x it appears as a relatively bright bluish star. It is best viewed with the highest magnification possible.