You may have thought the stars and planets near our solar system where pretty well mapped out, but that is not the case. Astronomers just discovered a frigid brown dwarf, an object halfway between a giant planet and a small star, near our solar system. A Pennsylvania State University research team found this new object using NASA’s Wide-field Infrared Survey Explorer (WISE) and Spitzer Space Telescopes.
The brown dwarf, called WISE J085510.83-071442, is 7.2 light years away. It is the Sun’s fifth closest neighbor, after Proxima Centauri, Alpha Centauri A and B, WISE 1049-5319 and Barnard’s Star.
WISE J0855.83-071442 is between -48 and -13 degrees Celsius, making it the coldest brown dwarf yet discovered. Some previously discovered brown dwarfs have been close to room temperature. In 2011, for example, astronomers identified a brown dwarf with a surface temperature of 25 degrees Celsius (80 degrees Fahrenheit).
WISE J085510.83-071442 is small too, between three and 10 times the mass of Jupiter. This low mass caused some difficulty in determining if the new object was a large gas giant or a brown dwarf. If the current mass estimate is accurate, this would make this newly discovered brown dwarf one of the smallest known.
Aside from just telling us more about the Sun’s neighborhood, this newly discovered brown dwarf could tell us a lot about the atmospheres of cold planets, said Kevin Luhman of Penn State. Luhman is a professor of astronomy and physics at Penn State and a researcher at the Penn State Center for Exoplanets and Habitable Worlds.
In 2013 scientists detected a fast-moving object in WISE data. A closer look at infrared images of that part of the sky revealed an object that was later identified as a brown dwarf rather than a planet. The NASA telescope data revealed a remarkably cold new stellar neighbor, but one of several brown dwarfs known to exist.
This new neighbor is a poor choice for future space exploration. Even if the means to go there existed, the intense cold makes it almost impossible that any orbiting planets would be habitable.
Detecting a brown dwarf is tricky because they do not emit much heat. A star fuses hydrogen and other elements to generate energy, but a brown dwarf does not. In fact, this is the key distinction between a brown dwarf and a star, with size being the other important factor. Infrared light can give away a brown dwarf, so this is the typical method to detect them.
In March of 2013, Luhman found another pair of brown dwarfs about 6.5 light years away. In previous work, Luhman demonstrated that the outer solar system probably does not contain a large, undiscovered planet.
Michael Werner, project scientist for the Spitzer telescope at NASA’s Jet Propulsion Laboratory noted that “we still do not have a complete inventory of the Sun’s nearest neighbors” after decades of work.
Brown dwarfs may be common in the galaxy. A 2012 estimate based on WISE data indicated that the Milky Way contains about six normal stars for every brown dwarf. Previous work had suggested that brown dwarfs were as common as regular stars.
This new, cool neighbor makes this region of space a bit more crowded, and promises to add to our understanding of how both planets and brown dwarfs work. WISE J085510.83-071442 also sets a new record. NASA’s telescopes have, in other studies found many new stellar neighbors over the years.
By Chester Davis