Abell 39 is a low
surface brightnessSurface brightness is a concept used in astronomy when describing extended astronomical objects such as galaxies and nebulae.-General description:...
planetary nebulaA planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas and plasma ejected during the asymptotic giant branch phase of certain types of stars late in their life...
in the constellation of
HerculesHercules is a constellation. It is named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today...
. It is the 39
th entry in
George Abell'sGeorge Ogden Abell was an astronomer at UCLA. He worked as a research astronomer, teacher, administrator, popularizer of science and education, and skeptic. Abell received his B.S. , M.S. and Ph.D. from the California Institute of Technology...
1966 Abell Catalog of Planetary Nebulae (and 27
th in his 1955 catalog) of 86 old planetary nebulae which either Abell or
Albert George WilsonAlbert George Wilson is an American astronomer.He was born in Houston, Texas. He received his Ph.D. in mathematics from Caltech in 1947; his thesis title was Axially Symmetric Thermal Stresses in a Semi-Infinite Solid....
discovered before August 1955 as part of the
National Geographic Society - Palomar Observatory Sky SurveyThe National Geographic Society - Palomar Observatory Sky Survey is a major photographic survey of the night sky completed at Palomar Observatory in 1958.-Observations:...
. It is estimated to be about 6,800
light-yearAs defined by the International Astronomical Union , a light-year is the distance that light travels in a vacuum in one Julian year.The speed of light is 299,792,458 metres per second...
s from earth and 4,600 light-years above the Galactic plane. It is almost perfectly spherical and also one of the largest known spheres with a radius of about 2.5 light-years.
Its central star is slightly west of center by about 2″ or 0.1 light-years.
Abell 39 is a low
surface brightnessSurface brightness is a concept used in astronomy when describing extended astronomical objects such as galaxies and nebulae.-General description:...
planetary nebulaA planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas and plasma ejected during the asymptotic giant branch phase of certain types of stars late in their life...
in the constellation of
HerculesHercules is a constellation. It is named after Hercules, the Roman mythological hero adapted from the Greek hero Heracles. Hercules was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations today...
. It is the 39
th entry in
George Abell'sGeorge Ogden Abell was an astronomer at UCLA. He worked as a research astronomer, teacher, administrator, popularizer of science and education, and skeptic. Abell received his B.S. , M.S. and Ph.D. from the California Institute of Technology...
1966 Abell Catalog of Planetary Nebulae (and 27
th in his 1955 catalog) of 86 old planetary nebulae which either Abell or
Albert George WilsonAlbert George Wilson is an American astronomer.He was born in Houston, Texas. He received his Ph.D. in mathematics from Caltech in 1947; his thesis title was Axially Symmetric Thermal Stresses in a Semi-Infinite Solid....
discovered before August 1955 as part of the
National Geographic Society - Palomar Observatory Sky SurveyThe National Geographic Society - Palomar Observatory Sky Survey is a major photographic survey of the night sky completed at Palomar Observatory in 1958.-Observations:...
. It is estimated to be about 6,800
light-yearAs defined by the International Astronomical Union , a light-year is the distance that light travels in a vacuum in one Julian year.The speed of light is 299,792,458 metres per second...
s from earth and 4,600 light-years above the Galactic plane. It is almost perfectly spherical and also one of the largest known spheres with a radius of about 2.5 light-years.
Central star
Its central star is slightly west of center by about 2″ or 0.1 light-years. This offset does not appear to be due to interaction with the
interstellar mediumIn astronomy, the interstellar medium is the gas and dust that pervade interstellar space: the matter that exists between the star systems within a galaxy. It fills interstellar space and blends smoothly into the surrounding intergalactic space...
, but instead, it is hypothesized that a small asymmetric
mass ejection has accelerated the central star. The mass of the central star is estimated to be about 0.61
M☉The solar mass , , is a standard way to express mass in astronomy, used to describe the masses of other stars and galaxies. It is equal to the mass of the Sun, about two nonillion kilograms or about 332,950 times the mass of the Earth or 1,048 times the mass of Jupiter.The solar mass can be...
with the material in the planetary nebula comprising an additional 0.6 M
☉.
This planetary nebula has a nearly uniform spherical shell. However, the eastern
limbLimb can refer to:*Limb , an appendage of a human or animal*Limb darkening, in astronomy, the appearance of the border of the disk of a celestial body*Limb Music, a record label*Limb , a compilation album by Foetus...
of the nebula is 50% more luminous than the western limb. Additionally, irregularities in the surface brightness are seen across the face of the shell. The source of the east-west asymmetry is not known but it could be related to the offset of the central star.
Structure and composition
The bright rim of the planetary nebula has an average thickness of about 10″.1 or about 0.34 light-years. There is a faint halo that extends about 18″ beyond the bright rim giving a complete diameter of around 190″ under the assumption that this emission is uniform around the planetary nebula.
This planetary nebula has been expanding for an estimated 22,100 years, based on an assumed expansion velocity between 32 and 37 km/s and a 0.78 parsec radius.
Background
galaxiesA galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek root galaxias [γαλαξίας], meaning "milky," a reference...
are visible near the nebula, and some can be seen through the translucent nebula.
OxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
is only about half as abundant in the nebula as it is in our own
sunThe Sun is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 99.86% of the Solar System's mass....
.
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