WD 0137-349 is a

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in ...

in the constellation of

Sculptor Sculpture is the branch of the visual arts that operates in three dimensions. Sculpture is the three-dimensional art work which is physically presented in the dimensions of height, width and depth. It is one of the plastic arts. Durable ...

. It is located about 330

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 101 ...

s (100

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, a ...

s) away, and appears exceedingly faint with an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of 15.33. It is composed of a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...

with a

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen (hydrogen-1, 1H) into helium in their cores, unlike a main sequence, main-sequence star. Instead, they have ...

in orbit around it, and is one of the few systems composed of a white dwarf and an associated brown dwarf. The brown dwarf orbits with a period of 116 minutes, or nearly 2 hours.

Properties

The primary is a typical

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

white dwarf, as indicated by its spectral type of DA. It has about 39% of the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared rad ...

's mass and is only 1.86% as wide (12,900 km). With a high

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 16,500 K, it emits radiation mostly in the

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiati ...

range. The brown dwarf, designated WD 0137-349B, can be detected from an

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 ofte ...

. Although it glows with an effective temperature of 1300 to 1400 K, the side facing the white dwarf's intercepts 1% of its light, and heats it up to around 2000 K. The "night" side spectrum of WD 0137-349B therefore matches that of a mid-

T-type The T-Type name was used in a series of Buick automobiles that were popular during the 1980s. This marketing approach for Buick products was a revival of a similar approach used in the 1960s (and later revived in the 1990s) with the Buick GS desi ...

brown dwarf, while the "day" side spectrum matches that of an early L-type brown dwarf. The brown dwarf is suspected to be a white dwarf or even a

strange star A strange star is a hypothetical astronomical object, a quark star made of strange quark matter. Strange stars might exist without regard to the Bodmer–Witten assumption of stability at near-zero temperatures and pressures, as strange quark mat ...

, as a hydrogen-dominated substellar object may be unstable in such a small orbit.

Evolution

The brown dwarf is known to have survived being engulfed when the primary star was 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 outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...

, because it was relatively massive. At that time, the red giant had a radius of . It is thought that the red giant phase of the current white dwarf was shortened from around 100 million years on average, to a few decades—while the brown dwarf was within the red giant, it hastened the expulsion of matter during this phase by rapidly heating gas and accreting a portion of it. During this phase,

drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adj ...

from the red giant also decreased the orbital speed of the brown dwarf, causing it to fall inwards. The orbit of the brown dwarf is slowly decaying. In about 1.4 billion years, it is thought that the orbit of the brown dwarf will have decayed sufficiently to allow the white dwarf to draw matter away and accrete it on its surface, leading to a

cataclysmic variable In astronomy, cataclysmic variable stars (CVs) are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state. They were initially called novae (), since ones with an outburst brightness visible to ...

. As of 2006, this is the coldest known companion to a white dwarf. This brown dwarf was also the object with the lowest mass known to have survived being engulfed by a red giant. Previously, only

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave (TV channel), Dave since 2009, gaining a ...

s had been known to survive being enveloped during a red giant phase. It is thought that objects smaller than 20

Jupiter mass 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 is b ...

es would have evaporated.

Post common envelope white dwarf-brown dwarf binaries

WD 0137-349 represents the first confirmed post common envelope binary (PCEB) containing a white dwarf and a brown dwarf. As of 2018 only 8 of these wd+bd PCEBs are known. The first with a confirmed spectral type was

GD 1400 GD, Gd, or gd may refer to: Arts and entertainment * G-Dragon (born 1988), leader of the South Korean musical group Big Bang * Grateful Dead, an American rock band * Green Day, an American rock band * ''Geometry Dash'', a rhythm-based video game ...

, but this second confirmed wd+bd binary after GD 165B was confirmed as a PCEB in 2011, five years later than WD 0137-349.

References

External links

* * {{DEFAULTSORT:WD 0137-349 White dwarfs Brown dwarfs L-type stars Spectroscopic binaries Sculptor (constellation) J01394284-3442393