NGC 6302
Encyclopedia
NGC 6302 is a bipolar
planetary nebula
in the constellation Scorpius
. The structure in the nebula is among the most complex ever observed in planetary nebulae. The spectrum of NGC 6302 shows that its central star is one of the hottest stars in the galaxy, with a surface temperature in excess of 200,000 K, implying that the star from which it formed must have been very large (cf. PG 1159 star
).
The central star, a white dwarf
, was only recently discovered , using the upgraded Wide Field Camera 3
on board the Hubble Space Telescope
. The star has a current mass of around 0.64 solar masses. It is surrounded by a particularly dense equatorial disc composed of gas and dust. This dense disc is postulated to have caused the star's outflows to form a bipolar structure similar to an hour-glass. This bipolar structure shows many interesting features seen in planetary nebulae such as ionization walls, knots and sharp edges to the lobes.
, this object has been known since at least 1888. The earliest known study of NGC 6302 is by Edward Emerson Barnard, who drew and described it in 1907 .
Since then it has been the focus of many works and displays many interesting characteristics worthy of study. Interest in recent years has shifted from discussions over the excitation method in the nebula (shock-excitation or photo-ionisation) to the properties of the large dust component.
It featured in some of the first images released after the final servicing mission of the Hubble Space Telescope in September 2009..
) similar to that found in Menzel 3 . The nebula is orientated at an angle of 12.8° against the plane of the sky.
This planetary nebula contains a prominent northwest lobe which extends up to 3′.0 away from the central star and is estimated to have formed from an eruptive event around 1,900 years ago. It has a circular part whose walls precisely follow a Hubble-type outflow (where outflow speed is proportional to distance from the central source). At an angular distance of 1′.71 from the central star, the flow velocity of this lobe is measured to be 263 km/s. At the extreme periphery of the lobe, the outward velocity exceeds 600 km/s. The western edge of the lobe displays characteristics suggestive of a collision with pre-existing globules of gas which modified the outflow in that region .
of the Hubble Space Telescope
revealed the faint star at the centre . A temperature of 200,000 Kelvin is indicated, and a mass of 0.64 solar masses. The original mass of the star was much higher, but most was ejected in the event which created the planetary nebula. The luminosity and temperature of the star indicate it has ceased nuclear burning and is on its way to becoming a white dwarf
, fading at a predicted rate of 1% per year.
, with other features which have been interpreted as the first extra-solar detection of carbonates . This detection has been disputed, due to the difficulties in forming carbonates in a non-aqueous environment . The dispute remains unresolved.
One of the most interesting characteristics of the dust detected in NGC 6302 is the existence of both oxygen-rich material (i.e. silicates) and carbon-rich material (i.e. poly-aromatic-hydrocarbons or PAHs) . Stars are usually either O-rich or C-rich, the change from the former to the latter occurring late in the evolution of the star due to nuclear and chemical changes in the star's atmosphere. NGC 6302 belongs to a group of objects where hydrocarbon molecules formed in an oxygen-rich environment
.
Bipolar 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...
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...
in the constellation Scorpius
Scorpius
Scorpius, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is . It lies between Libra to the west and Sagittarius to the east...
. The structure in the nebula is among the most complex ever observed in planetary nebulae. The spectrum of NGC 6302 shows that its central star is one of the hottest stars in the galaxy, with a surface temperature in excess of 200,000 K, implying that the star from which it formed must have been very large (cf. PG 1159 star
PG 1159 star
A PG 1159 star, often also called a pre-degenerate, is a star with a hydrogen-deficient atmosphere which is in transition between being the central star of a planetary nebula and being a hot white dwarf...
).
The central star, a 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...
, was only recently discovered , using the upgraded Wide Field Camera 3
Wide Field Camera 3
The Wide Field Camera 3 is the Hubble Space Telescope's last and most technologically advanced instrument to take images in the visible spectrum...
on board 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...
. The star has a current mass of around 0.64 solar masses. It is surrounded by a particularly dense equatorial disc composed of gas and dust. This dense disc is postulated to have caused the star's outflows to form a bipolar structure similar to an hour-glass. This bipolar structure shows many interesting features seen in planetary nebulae such as ionization walls, knots and sharp edges to the lobes.
Observation history
As it is included in the New General CatalogueNew General Catalogue
The 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...
, this object has been known since at least 1888. The earliest known study of NGC 6302 is by Edward Emerson Barnard, who drew and described it in 1907 .
Since then it has been the focus of many works and displays many interesting characteristics worthy of study. Interest in recent years has shifted from discussions over the excitation method in the nebula (shock-excitation or photo-ionisation) to the properties of the large dust component.
It featured in some of the first images released after the final servicing mission of the Hubble Space Telescope in September 2009..
Characteristics
NGC 6302 has a complex morphology, which may be approximated as bipolar with two primary lobes, though there is evidence for a second pair of lobes that may have belonged to a previous phase of mass loss. A dark lane runs through the waist of the nebula obscuring the central star at all wavelengths . Observations of NGC 6302 suggest that there may be an orthogonal skirt (or chakramChakram
The chakram , sometimes called a war quoit, is a throwing weapon from India. Its shape is of a flat metal hoop with a sharp outer edge from in diameter...
) similar to that found in Menzel 3 . The nebula is orientated at an angle of 12.8° against the plane of the sky.
This planetary nebula contains a prominent northwest lobe which extends up to 3′.0 away from the central star and is estimated to have formed from an eruptive event around 1,900 years ago. It has a circular part whose walls precisely follow a Hubble-type outflow (where outflow speed is proportional to distance from the central source). At an angular distance of 1′.71 from the central star, the flow velocity of this lobe is measured to be 263 km/s. At the extreme periphery of the lobe, the outward velocity exceeds 600 km/s. The western edge of the lobe displays characteristics suggestive of a collision with pre-existing globules of gas which modified the outflow in that region .
Central star
The central star, among the hottest stars known, had escaped detection because of a combination of its high temperature (so that it radiates mainly in the ultraviolet), the dusty torus (which absorbs a large fraction of the light from the central regions, especially in the ultraviolet) and the bright background from the star. It was not seen in the first HST images . But the improved resolution and sensitivity of the new Wide Field Camera 3Wide Field Camera 3
The Wide Field Camera 3 is the Hubble Space Telescope's last and most technologically advanced instrument to take images in the visible spectrum...
of 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...
revealed the faint star at the centre . A temperature of 200,000 Kelvin is indicated, and a mass of 0.64 solar masses. The original mass of the star was much higher, but most was ejected in the event which created the planetary nebula. The luminosity and temperature of the star indicate it has ceased nuclear burning and is on its way to becoming a 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...
, fading at a predicted rate of 1% per year.
Dust chemistry
The prominent dark lane that runs through the centre of the nebula has been shown to have an extraordinary dust chemistry, showing evidence for multiple crystalline silicates, crystalline water ice and quartzQuartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, with other features which have been interpreted as the first extra-solar detection of carbonates . This detection has been disputed, due to the difficulties in forming carbonates in a non-aqueous environment . The dispute remains unresolved.
One of the most interesting characteristics of the dust detected in NGC 6302 is the existence of both oxygen-rich material (i.e. silicates) and carbon-rich material (i.e. poly-aromatic-hydrocarbons or PAHs) . Stars are usually either O-rich or C-rich, the change from the former to the latter occurring late in the evolution of the star due to nuclear and chemical changes in the star's atmosphere. NGC 6302 belongs to a group of objects where hydrocarbon molecules formed in an oxygen-rich environment
.