Ring Nebula
Encyclopedia
The famously named "Ring Nebula" (also catalogued as Messier
57, M57 or NGC 6720) appears in the northern constellation
of Lyra
and is located in the Carina–Sagittarius Arm. It is one of the most prominent examples of a planetary nebula
, the gaseous remains of a red giant
star that has ended its life by expelling its material into the surrounding interstellar medium.
in January, 1779, who reported that it was "...as large as Jupiter and resembles a planet which is fading." Later the same month, Charles Messier
independently found the same nebula while searching for comet
s. It was then entered into his catalogue as the 57th object. Messier and William Herschel
also speculated that the nebula was formed by multiple faint stars that were unable to resolve with his telescope.
In 1800, Count Friedrich von Hahn
discovered the faint central star in the heart of the nebula. In 1864, William Huggins
examined the spectra of multiple nebulae, discovering that some of these objects, including M57, displayed the spectra of bright emission lines characteristic of fluorescing glowing gases. Huggins concluded that most planetary nebulae were not composed of unresolved stars, as had been previously suspected, but were nebulosities.
, which forms the northwestern vertex of the Summer Triangle
asterism. It lies midway between β
and γ Lyrae
, making it an easy target for amateur astronomers.
The nebula is best observed using apertures of at least 20 cm (8-inches), but even a 7.5 cm (3-inch) telescope will reveal its elliptical ring shape. Larger instruments will show a few darker zones on the eastern and western edges of the ring, and some faint nebulosity inside the disk. The central star, at magnitude 14.8, is difficult to spot.
M57 is 0.7 kpc (2,300 light-year
s) from Earth. It has a visual magnitude
of 8.8v and photographic magnitude
of 9.7p. Photographically, over a period of 50 years, the rate of nebula expansion is roughly 1 arcsecond per century, which corresponds from spectroscopic observations to 20–30 km−1). M57 is illuminated by a central white dwarf
or planetary nebula nucleus (PNN) of 15.75v visual magnitude
, whose mass is approximately 1.2 MΘ (in solar mass
es.)
All the interior parts of this nebula have a blue-green tinge that is caused by the doubly ionized oxygen
emission lines at 495.7 and 500.7 nm. These observed so-called "forbidden lines" occur only in conditions of very low density containing a few atoms per cubic centimeter. In the outer region of the ring, part of the reddish hue is caused by hydrogen
emission at 656.3 nm, forming part of the Balmer series
of lines. Forbidden lines of ionized nitrogen
or [N II] contributes to the reddishness at 654.8 and 658.3 nm.
nebulae, whose thick equatorial rings visibly extend the structure through its main axis of symmetry. It appears to be a prolate spheroid
with strong concentrations of material along its equator
. From Earth, the symmetrical axis is viewed at about 30°. Overall, the observed nebulosity has been currently estimated to be expanding for approximately 1,610±240 years.
Structural studies find this planetary exhibits knots characterized by well developed symmetry. However, these are only silhouettes visible against the background emission of the nebula's equatorial ring. M57 may include internal N II emission lines located at the knots' tips that face the PNN; however, most of these knots are neutral and appear only in extinction lines. Their existence shows they are probably only located closer to the ionization front than those found in the Lupus
planetary IC 4406
. Some of the knots do exhibit well-developed tails which are often detectable in optical thickness from the visual spectrum.
(now part of Szombathely). Within the last two thousand years, the central star of the Ring Nebula has left the asymptotic giant branch
after exhausting its supply of hydrogen
fuel. Thus it no longer produces its energy through nuclear fusion
and, in evolutionary
terms, it is now becoming a compact white dwarf
star.
The PNN now consists primarily of carbon
and oxygen
with a thin outer envelope composed of lighter elements. Its mass is about 0.61–0.62 solar mass
, with a surface temperature of 125,000±5,000 K. Currently it is 200 times more luminous than the Sun
, but its apparent magnitude
is only +15.75.
Messier object
The Messier objects are a set of astronomical objects first listed by French astronomer Charles Messier in 1771. The original motivation of the catalogue was that Messier was a comet hunter, and was frustrated by objects which resembled but were not comets...
57, M57 or NGC 6720) appears in the northern 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....
of Lyra
Lyra
Lyra is a small constellation. It is one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations recognized by the International Astronomical Union. Its principal star, Vega — a corner of the Summer Triangle — is one of the brightest...
and is located in the Carina–Sagittarius Arm. It is one of the most prominent examples of a planetary nebula
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...
, the gaseous remains of a red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
star that has ended its life by expelling its material into the surrounding interstellar medium.
History
This nebula was discovered by Antoine Darquier de PellepoixAntoine Darquier de Pellepoix
Antoine Darquier de Pellepoix was a French astronomer. He discovered the Ring Nebula in 1779.-External links:* *...
in January, 1779, who reported that it was "...as large as Jupiter and resembles a planet which is fading." Later the same month, Charles Messier
Charles Messier
Charles Messier was a French astronomer most notable for publishing an astronomical catalogue consisting of deep sky objects such as nebulae and star clusters that came to be known as the 110 "Messier objects"...
independently found the same nebula while searching for comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s. It was then entered into his catalogue as the 57th object. Messier and William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...
also speculated that the nebula was formed by multiple faint stars that were unable to resolve with his telescope.
In 1800, Count Friedrich von Hahn
Friedrich von Hahn
Friedrich II. Graf von Hahn was a German nobleman, a philosopher and astronomer.Von Hahn was born in Neuhaus, Holstein...
discovered the faint central star in the heart of the nebula. In 1864, William Huggins
William Huggins
Sir William Huggins, OM, KCB, FRS was an English amateur astronomer best known for his pioneering work in astronomical spectroscopy.-Biography:...
examined the spectra of multiple nebulae, discovering that some of these objects, including M57, displayed the spectra of bright emission lines characteristic of fluorescing glowing gases. Huggins concluded that most planetary nebulae were not composed of unresolved stars, as had been previously suspected, but were nebulosities.
Observation
M57 is located south of the bright star VegaVega
Vega is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus...
, which forms the northwestern vertex of the Summer Triangle
Summer Triangle
The Summer Triangle is an astronomical asterism involving an imaginary triangle drawn on the northern hemisphere's celestial sphere, with its defining vertices at Altair, Deneb, and Vega, being the brightest stars in the three constellations of Aquila, Cygnus, and Lyra.The English term was...
asterism. It lies midway between β
Beta Lyrae
Beta Lyrae is a binary star system approximately 882 light-years away in the constellation Lyra. Beta Lyrae has the traditional name Sheliak , from الشلياق šiliyāq, the Arabic name of the constellation Lyra.Beta Lyrae is an eclipsing semi-detached binary system made up of a B7II primary star and...
and γ Lyrae
Gamma Lyrae
Gamma Lyrae is a star in the constellation Lyra. It has the traditional names Sulafat , from the Arabic al-sulḥafāt "turtle", and Jugum, from the Latin "yoke"...
, making it an easy target for amateur astronomers.
The nebula is best observed using apertures of at least 20 cm (8-inches), but even a 7.5 cm (3-inch) telescope will reveal its elliptical ring shape. Larger instruments will show a few darker zones on the eastern and western edges of the ring, and some faint nebulosity inside the disk. The central star, at magnitude 14.8, is difficult to spot.
Properties
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s) from Earth. It has a visual magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of 8.8v and photographic magnitude
Photographic magnitude
Before the advent of photometers which accurately measure the brightness of astronomical objects, the apparent magnitude of an object was obtained by taking a picture of it with a camera. These images, made on photoemulsive film or plates, were more sensitive to the blue end of the visual spectrum...
of 9.7p. Photographically, over a period of 50 years, the rate of nebula expansion is roughly 1 arcsecond per century, which corresponds from spectroscopic observations to 20–30 km−1). M57 is illuminated by a 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...
or planetary nebula nucleus (PNN) of 15.75v visual magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
, whose mass is approximately 1.2 MΘ (in solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
es.)
All the interior parts of this nebula have a blue-green tinge that is caused by the doubly ionized oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
emission lines at 495.7 and 500.7 nm. These observed so-called "forbidden lines" occur only in conditions of very low density containing a few atoms per cubic centimeter. In the outer region of the ring, part of the reddish hue is caused by hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
emission at 656.3 nm, forming part of the Balmer series
Balmer series
The Balmer series or Balmer lines in atomic physics, is the designation of one of a set of six different named series describing the spectral line emissions of the hydrogen atom....
of lines. Forbidden lines of ionized nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
or [N II] contributes to the reddishness at 654.8 and 658.3 nm.
Nebula structure
M57 is an example of the class of planetary nebulae known as bipolarBipolar nebula
A bipolar nebula is a distinctive nebular formation characterized by an axially symmetric bi-lobed appearance.Many, but not all, planetary nebulae exhibit an observed bipolar structure...
nebulae, whose thick equatorial rings visibly extend the structure through its main axis of symmetry. It appears to be a prolate spheroid
Prolate spheroid
A prolate spheroid is a spheroid in which the polar axis is greater than the equatorial diameter. Prolate spheroids stand in contrast to oblate spheroids...
with strong concentrations of material along its equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
. From Earth, the symmetrical axis is viewed at about 30°. Overall, the observed nebulosity has been currently estimated to be expanding for approximately 1,610±240 years.
Structural studies find this planetary exhibits knots characterized by well developed symmetry. However, these are only silhouettes visible against the background emission of the nebula's equatorial ring. M57 may include internal N II emission lines located at the knots' tips that face the PNN; however, most of these knots are neutral and appear only in extinction lines. Their existence shows they are probably only located closer to the ionization front than those found in the Lupus
Lupus (constellation)
Lupus is a constellation in the southern sky. Its name is Latin for wolf. Lupus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations...
planetary IC 4406
IC 4406
IC 4406 is a planetary nebula near the western border of the constellation Lupus, the Wolf. It has dust clouds and has the shape of a torus. Despite this, it looks somewhat rectangular because it is seen from its side as viewed from Earth, almost in the plane of its equator.-Structure:IC 4406 is...
. Some of the knots do exhibit well-developed tails which are often detectable in optical thickness from the visual spectrum.
Planetary nebula nucleus (PNN)
The central PNN was discovered by Hungarian astronomer Jenő Gothard on September 1, 1886 from images taken at his observatory in Herény, near SzombathelySzombathely
Szombathely is the 10th largest city in Hungary. It is the administrative centre of Vas county in the west of the country, located near the border with Austria...
(now part of Szombathely). Within the last two thousand years, the central star of the Ring Nebula has left the asymptotic giant branch
Asymptotic Giant Branch
The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass stars. This is a period of stellar evolution undertaken by all low to intermediate mass stars late in their lives....
after exhausting its supply of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
fuel. Thus it no longer produces its energy through nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
and, in evolutionary
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...
terms, it is now becoming a compact 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...
star.
The PNN now consists primarily of 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 oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
with a thin outer envelope composed of lighter elements. Its mass is about 0.61–0.62 solar mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
, with a surface temperature of 125,000±5,000 K. Currently it is 200 times more luminous than 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...
, but its apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
is only +15.75.
See also
- List of planetary nebulae
- Messier objectMessier objectThe Messier objects are a set of astronomical objects first listed by French astronomer Charles Messier in 1771. The original motivation of the catalogue was that Messier was a comet hunter, and was frustrated by objects which resembled but were not comets...
- New General CatalogueNew General CatalogueThe New General Catalogue of Nebulae and Clusters of Stars is a well-known catalogue of deep sky objects in astronomy. It contains 7,840 objects, known as the NGC objects...
- List of Messier objects
External links
- M57: Calar Alto Observatory
- SEDS: Messier Object 57
- Astronomy Picture of the DayAstronomy Picture of the DayAstronomy Picture of the Day is a website provided by NASA and Michigan Technological University . According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation written by a professional astronomer."The photograph is not necessarily...
- Infrared Ring Nebula 2005 March 11
- Ring Nebula Deep Field 2009 November 6
- M57: The Ring Nebula 2009 November 15
- NightSkyInfo.com - The Ring Nebula
- M57 The Ring Nebula in Lyra
- M57 at ESA/Hubble