WISE 0855−0714 (full designation WISE J085510.83−071442.5, or W0855 for short) is a brown dwarf of spectral class Y4, located 7.4 light-years (2.3 parsecs) from the Sun in the constellation Hydra. It is the fourth-closest stellar or substellar system to the Sun and was discovered by Kevin Luhman in 2013 using data from the Wide-field Infrared Survey Explorer (WISE). It is the coldest brown dwarf found yet, having a temperature of about 276 K (3 °C; 37 °F). It has an estimated mass between 3 and 10 Jupiter masses, which makes it a planetary-mass object below the 13-Jupiter-mass rough limit for deuterium fusion.
Discovery WISE 0855−0714 was first imaged by the WISE telescope on 4 May 2010 during its primary mission of surveying the entire sky. It was later discovered by Kevin Luhman in March 2013, who noticed the object's unusually high proper motion while searching for potential binary companions of the Sun in WISE images. In the interest of confirming the object's spectral properties and nearby distance to the Sun, Luhman made follow-up observations with the Spitzer Space Telescope and the Gemini North telescope in 2013–2014. The discovery of the object was announced in a NASA press release in April 2014.
Distance and proper motion Based on direct observations, WISE 0855−0714 has a large parallax of 439.0±2.4 mas, which corresponds to a distance of around 2.28±0.01 parsecs (7.43±0.04 light-years). This makes WISE 0855−0714 the fourth-closest stellar or substellar system to the Sun. WISE 0855−0714 also has an exceptionally high proper motion of 8,151.6±1.8 mas/yr, the third highest after Barnard's Star (10,300 mas/yr) and Kapteyn's Star (8,600 mas/yr).
Physical characteristics
Mass and age The mass and age of WISE 0855−0714 are neither known with certainty, but can be constrained with its known present-day temperature. The age of WISE 0855−0714 depends on its mass; a lower mass would lead to a faster rate of cooling and thus a younger age for WISE 0855−0714, whereas a higher mass would lead to a slower rate of cooling and thus an older age for WISE 0855−0714. Assuming an age range of 1–10 billion years, evolutionary models for brown dwarfs predict that WISE 0855−0714 should have a mass between 3 and 10 MJup. The mass could also be obtained with measurements of the surface gravity and radius of the brown dwarf. One 2024 study obtained two values of 103.93 and 104.03 cgs for the surface gravity from two different data sets. Assuming a radius of one Jupiter radius (RJup) for the brown dwarf, they obtained mass values of 3.44 and 4.33 MJup, respectively. All these mass values are in the planetary mass range.
Classification As of 2003, the International Astronomical Union considers an object with a mass above 13 MJup, capable of fusing deuterium, to be a brown dwarf. WISE 0855–0714, being a free-floating object with a mass lower than the deuterium burning limit, would be called a free-floating planetary mass object, although the literature classifies it as a brown dwarf. If the distinction is based on how the object formed then it might be considered a failed star, a theory advanced for the object Cha 110913−773444.
Temperature, size and luminosity WISE 0855–0714 is the coldest-known brown dwarf, with an effective temperature of 276 K (3 °C; 37 °F), as estimated from evolutionary models based on its bolometric luminosity of 6.03×10−8 L☉ and an assumed age between 0.5 and 10 billion years. The luminosity and temperature imply a radius of 0.107 solar radii (R☉), or 1.045 RJup. Atmospheric models matching the NIRSpec spectrum are well fitted with a temperature of 285 K (12 °C; 53 °F), somewhat higher than that estimated from evolution models. Since WISE 0855−0714 is an isolated object, its luminosity primarily comes from thermal radiation. WISE 0855−0714's temperature is low enough that it roughly matches room temperature, which means its luminosity is very low and it primarily emits infrared radiation as thermal radiation. Hence, it is best observed with infrared telescopes such as WISE and the James Webb Space Telescope (JWST). WISE 0855−0714 has been detected in spectral wavelengths as short as 1.15 μm—in this near-infrared wavelength, the object appears extremely dim with an apparent magnitude of 26.3. WISE 0855−0714's brightness decreases with decreasing wavelength, so the object is practically invisible in visible light.
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