GJ 440
Encyclopedia
GJ 440 (also known by the designation WD 1142-645) is a white dwarf
star
located 15 light years from the solar system
. According to a 2009 paper, it is the fourth closest known white dwarf to the Sun (after Sirius B, Procyon B, and van Maanen's star
.)
White dwarfs are no longer generating energy at their cores through nuclear fusion
, and instead are steadily radiating away their remaining heat. GJ 440 has a DQ spectral classification, indicating that it is a rare type of white dwarf which displays evidence of atomic or molecular carbon
in its spectrum.
GJ 440 has only 75% of the Sun's mass, but it is the remnant of a massive main sequence
star that had an estimated 4.4 solar mass
es. While it was on the main sequence, it probably was a spectral class B star (in the range B4-B9). Most of the star's original mass was shed after it passed into the asymptotic giant branch
stage, just prior to becoming a white dwarf.
A survey with the Hubble Space Telescope
revealed no visible orbiting companions, at least down to the limit of detection.
GJ 440 may be a member of the Wolf 219 moving group, which has seven possible members. These stars share a similar motion through space, which may indicate a common origin. This group has an estimated space velocity of 160 km/s and is following a highly eccentric orbit
through the Milky Way
galaxy.
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
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
located 15 light years from the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
. According to a 2009 paper, it is the fourth closest known white dwarf to the Sun (after Sirius B, Procyon B, and van Maanen's star
Van Maanen's star
Van Maanen's star is a white dwarf star. Out of the white dwarfs known, it is the third closest to the Sun, after Sirius B and Procyon B, in that order, and the closest known solitary white dwarf...
.)
White dwarfs are no longer generating energy at their cores 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 instead are steadily radiating away their remaining heat. GJ 440 has a DQ spectral classification, indicating that it is a rare type of white dwarf which displays evidence of atomic or molecular 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...
in its spectrum.
GJ 440 has only 75% of the Sun's mass, but it is the remnant of a massive main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
star that had an estimated 4.4 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. While it was on the main sequence, it probably was a spectral class B star (in the range B4-B9). Most of the star's original mass was shed after it passed into 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....
stage, just prior to becoming a white dwarf.
A survey with 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 no visible orbiting companions, at least down to the limit of detection.
GJ 440 may be a member of the Wolf 219 moving group, which has seven possible members. These stars share a similar motion through space, which may indicate a common origin. This group has an estimated space velocity of 160 km/s and is following a highly eccentric orbit
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
through the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
galaxy.