Van Maanen 2, or van Maanen's Star, is the closest known solitary
white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
to the Solar System. It is a dense, compact
stellar remnant
In astronomy, the term compact object (or compact star) refers collectively to white dwarfs, neutron stars, and black holes. It could also include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects have a ...
no longer generating energy and has equivalent to about 68% of the Sun's mass but only 1% of its radius.
At a distance of 14.1 light-years it is the third closest of its type of star after
Sirius B
Sirius is the brightest star in the night sky. Its name is derived from the Greek word (Latin script: ), meaning 'glowing' or 'scorching'. The star is designated Canis Majoris, Latinized to Alpha Canis Majoris, and abbre ...
and
Procyon B, in that order.
Discovered in 1917 by Dutch–American astronomer
Adriaan van Maanen
Adriaan van Maanen (March 31, 1884 – January 26, 1946) was a Dutch-American astronomer. Born in Friesland, he studied astronomy at the University of Utrecht, earning his Ph.D. in 1911, and worked briefly at the University of Groningen. In 1 ...
,
Van Maanen 2 was the third white dwarf identified, after
40 Eridani B and Sirius B, and the first solitary example.
Observation history
While searching for a companion to the large-
proper-motion star
Lalande 1299, in 1917 Dutch–American astronomer
Adriaan van Maanen
Adriaan van Maanen (March 31, 1884 – January 26, 1946) was a Dutch-American astronomer. Born in Friesland, he studied astronomy at the University of Utrecht, earning his Ph.D. in 1911, and worked briefly at the University of Groningen. In 1 ...
discovered this star with an even larger proper motion a few
arcminute
A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...
s to the northeast. He estimated the annual proper motion of the latter as 3
arcsecond
A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...
s. This star had been captured on a plate taken November 11, 1896 for the
Carte du Ciel
The Carte du Ciel (; literally, 'Map of the Sky') and the Astrographic Catalogue (or Astrographic Chart) were two distinct but connected components of a massive international astronomical project, initiated in the late 19th century, to catalogue ...
Catalog of Toulouse and it showed an apparent magnitude of 12.3.
[ Prominent absorption features of calcium ]K-line
K-Line Electric Trains is a brand name of O gauge and S gauge model railway locomotives, rolling stock, and buildings. Formerly the brand name under which Chapel Hill, North Carolina–based MDK Inc. sold its products, K-Line was then acquired b ...
to H-beta
The Balmer series, or Balmer lines in atomic physics, is one of a set of six named series describing the spectral line emissions of the hydrogen atom. The Balmer series is calculated using the Balmer formula, an empirical equation discovered b ...
in the spectrum
A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...
led van Maanen to assign it a spectral classification of F0, and it was initially known as "van Maanen's F star".[
In 1918, American astronomer Frederick Seares obtained a refined visual magnitude of 12.34, but the distance to the star remained unknown.][ Two years later, van Maanen published a ]parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
estimate of 0.246″, giving it an absolute magnitude of +14.8. This made it the faintest F-type star known at that time.[ In 1923, Dutch-American astronomer Willem Luyten published a study of stars with large proper motions in which he identified what he called "van Maanen's star" as one of only three known ]white dwarf
A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
s, a term he coined.[ These are stars that have an unusually low absolute magnitude for their ]spectral class
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
, lying well below the main sequence
In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
on the Hertzsprung–Russell diagram
The Hertzsprung–Russell diagram (abbreviated as H–R diagram, HR diagram or HRD) is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities and their stellar classifications or effective temp ...
of stellar temperature vs. luminosity.[
The high mass density of white dwarfs was demonstrated in 1925 by American astronomer Walter Adams when he measured the ]gravitational redshift
In physics and general relativity, gravitational redshift (known as Einstein shift in older literature) is the phenomenon that electromagnetic waves or photons travelling out of a gravitational well lose energy. This loss of energy correspo ...
of Sirius B
Sirius is the brightest star in the night sky. Its name is derived from the Greek word (Latin script: ), meaning 'glowing' or 'scorching'. The star is designated Canis Majoris, Latinized to Alpha Canis Majoris, and abbre ...
as 21 km/s.[ In 1926, British astrophysicist ]Ralph Fowler
Sir Ralph Howard Fowler (17 January 1889 – 28 July 1944) was an English physicist, physical chemist, and astronomer.
Education
Ralph H. Fowler was born at Roydon, Essex, on 17 January 1889 to Howard Fowler, from Burnham, Somerset, and France ...
used the new theory of quantum mechanics
Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Addison-Wesley, 1989, It is ...
to show that these stars are supported by electron gas in a degenerate state.[ British astrophysicist ]Leon Mestel
Leon Mestel (5 August 1927 – 15 September 2017) was a British-Australian astronomer and astrophysicist and Emeritus Professor at the University of Sussex. His research interests were in the areas of star formation and structure, especially st ...
demonstrated in 1952 that the energy they emit is the surviving heat from bygone nuclear fusion
Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutrons, neutron by-products. The difference in mass between the reactants and products is manifested as either the rele ...
. He showed that the latter no longer occurs within a white dwarf, and calculated the internal temperature of van Maanen 2 as 6 million K. He gave a preliminary age estimate of 100 billion/''A'' years, where ''A'' is the mean atomic weight
Relative atomic mass (symbol: ''A''; sometimes abbreviated RAM or r.a.m.), also known by the deprecated synonym atomic weight, is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a giv ...
of the nuclei in the star.[
In 2016, it was discovered that a spectrographic plate of the star made in 1917 gives evidence – the earliest known – of planetary matter outside the ]Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...
,[ in the form of calcium absorption lines that indicate the presence of planetary material polluting the stellar atmosphere.
]
Characteristics
Van Maanen 2 is from the Sun in the constellation Pisces
Pisces may refer to:
*Pisces (astrology), an astrological sign
Astronomy
*Pisces (constellation), a constellation
** Pisces Overdensity, an overdensity of stars in the Milky Way's halo that is situated in the Pisces constellation
** Pisces II, a ...
, about 2° to the south of the star Delta Piscium
Delta Piscium (δ Piscium) is a solitary, orange-hued star in the zodiac constellation of Pisces. It has an apparent visual magnitude of +4.4, so it is bright enough to be faintly visible to the naked eye. Based upon an annual parallax sh ...
,[ with a relatively high ]proper motion
Proper motion is the astrometric measure of changes in the apparent places of stars or other celestial objects as they move relative to the center of mass of the Solar System. It is measured relative to the distant stars or a stable referenc ...
of 2.978″ annually along a position angle
In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the Celestial pole, north celestial pole (NCP), turning pos ...
of 155.538°.[ It is closer to the Sun than any other solitary white dwarf. It is too faint to be seen with the ]naked eye
Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...
.[ Like other white dwarfs, it is a very dense star: its mass has been estimated to be about 67% of the Sun's,][ yet it has only 1% of the ]Sun's radius
Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3:
1\,R_ = 6.957\ti ...
(1.23 times the Earth's radius
Earth radius (denoted as ''R''🜨 or ''R''E) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid (an oblate ellipsoid), the radius ranges from a maximum (equato ...
).[ The outer atmosphere has a temperature of approximately 6,110 K,][ which is relatively cool for a white dwarf. As all white dwarfs steadily radiate away their heat over time, this temperature can be used to estimate its age, thought to be around 3 billion years.][
The progenitor of this white dwarf had an estimated 2.6 solar masses and remained on the main sequence for about 900 million years. This gives the star an overall age of about 4.1 billion years. When this star left the main sequence, it expanded into a ]red giant
A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...
that reached a maximum radius of 1,000 times the current radius of the Sun, or about 4.6 astronomical unit
The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...
s. Any planets orbiting within this radius would have been engulfed in the star's extent.[
The ]stellar classification
In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...
of Van Maanen 2 is DZ8, having a helium atmosphere with a significant presence of heavier elements in its spectrum – what astronomers term metals
A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at the Fermi level, as against no ...
.[ Indeed, this star is the prototype (archetype in practice) for DZ white dwarfs. Physical models of white dwarfs used by today's astrophysicists show that elements with mass greater than helium would sink, all things being equal, below the ]photosphere
The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...
, leaving hydrogen and helium to be visible in the spectrum; for heavier elements to appear here requires a recent external source.[ It is unlikely that they were obtained from the ]interstellar medium
The interstellar medium (ISM) is the matter and radiation that exists in the outer space, space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as cosmic dust, dust and cosmic rays. It f ...
, since that is primarily composed of hydrogen and helium.[ Instead, the surface of the star was likely strewn with circumstellar material, such as from the remains of one or more rocky, ]terrestrial planet
A terrestrial planet, tellurian planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate, rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to ...
s.[ Later observations with the ]International Ultraviolet Explorer
International Ultraviolet Explorer (IUE or Explorer 57, formerly SAS-D) was the first Space telescope, space observatory primarily designed to take ultraviolet (UV) electromagnetic spectrum. The satellite was a collaborative project between NA ...
detected calcium, magnesium
Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
and iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
. This work also detected Lyman alpha
Lyman-alpha, typically denoted by Ly-α or Lyα, is a spectral line of hydrogen (or, more generally, of any one-electron atom) in the Lyman series. It is emitted when the atomic electron transitions from an ''n'' = 2 orbital to the gro ...
absorption, which shows that hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
is present in the atmosphere.
The total mass of metals in the atmosphere of Van Maanen 2 is estimated to be around 1021 g—about the same mass as a large moon such as Ariel
Ariel may refer to:
Film and television
*Ariel Award, a Mexican Academy of Film award
* ''Ariel'' (film), a 1988 Finnish film by Aki Kaurismäki
*, a Russian film directed by Yevgeni Kotov
* ''ARIEL Visual'' and ''ARIEL Deluxe'', a 1989 and 1991 ...
. These pollutants will sink deeper into the atmosphere on time scales of around three million years, which indicates the material is being replenished at a rate of 107 g/s. These materials could have been accreted in the form of multiple planetesimal
Planetesimals () are solid objects thought to exist in protoplanetary disks and debris disks. Believed to have formed in the Solar System about 4.6 billion years ago, they aid study of its formation.
Formation
A widely accepted theory of pla ...
s smaller than around 84 km colliding with the star.[
White dwarfs with a spectrum that indicates high levels of metal contamination of the photosphere often have a ]circumstellar disk
A Circumstellar disc (or circumstellar disk) is a torus, pancake or ring-shaped accretion disk of matter composed of gas, dust, planetesimals, asteroids, or collision fragments in orbit around a star. Around the youngest stars, they are the res ...
. In the case of van Maanen 2, observations at a wavelength of 24 μm
The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...
do not show the infrared excess
An infrared excess is a measurement of an astronomical source, typically a star, that in their spectral energy distribution has a greater measured infrared flux than expected by assuming the star is a blackbody radiator. Infrared excesses are of ...
that might be generated by a dusty disk. Instead there is a noticeable deficit. The predicted flux at 24 μm is 0.23 m Jy, whereas the measured value is . This deficit may be explained by collision-induced absorption in the atmosphere of the star,[ as seen in certain white dwarfs that have temperatures below 4,000 K, as a result of collisions between hydrogen molecules or between hydrogen molecules and helium.][
A paper published in 2015 found that, based upon the space velocity of this star, it made the closest approach 15,070 years ago as then it was from the Sun,][ although it uses an outdated and unreliable radial velocity measurement.][
]
Possible companion
The possibility of a substellar
A substellar object, sometimes called a substar, is an astronomical object, the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained (approximately 0.08 solar masses). This definition includes brown dwarfs and f ...
companion remains uncertain. As of 2004, one paper claimed detection of this,[ while another discounted this.][ As of 2008, observations with the ]Spitzer Space Telescope
The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003, that was deactivated when operations ended on 30 January 2020. Spitzer was the third space telescope dedicate ...
appear to rule out any companions within 1,200 AU of the star that have four Jupiter mass
The Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter ...
es or greater.[ No potential proper motion companions have been identified between an ]angular separation
Angular distance or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors in three-dimensional space, or the central angle subtended by the radii through two points on a sphere. When t ...
of out to 10°, ruling out objects with a mass of or greater.[
As of 2022 a candidate planet was detected via ]astrometry
Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other Astronomical object, celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, th ...
, with a mass between 0.4 and 1.1 Jupiter masses.
See also
* List of white dwarfs
* List of exoplanets and planetary debris around white dwarfs
This is a list of exoplanets and planetary debris disks around white dwarfs.
List of white dwarf exoplanets List of confirmed exoplanets
List of candidate exoplanets
List of exoplanets detected via timing
Circumbinary planet, Circumbin ...
* List of nearest stars and brown dwarfs
This list covers all known stars, white dwarfs, brown dwarfs, and sub-brown dwarfs within of the Sun. So far, 131 such objects have been found. Only List of nearest bright stars, 22 are bright enough to be visible without a telescope, for whi ...
* Stars named after people
Over the past few centuries, a small number of stars have been named after individual people. It is common in astronomy for objects to be given names, in accordance with accepted astronomical naming conventions. Most stars have not been given prop ...
Notes
References
{{DEFAULTSORT:Van Maanen 2
White dwarfs
Local Bubble
Pisces (constellation)
0035
003829
TIC objects
Van Maanen's Star
028