Astronomers and citizen scientists from the Backyard Worlds: Planet 9 project have announced an unprecedented census of 525 L, T, and Y-type dwarfs within 65 light-years of the Sun, including 38 new discoveries. By determining the distances to all the objects in the census, the team has been able to build a 3D map of the distribution of cool brown dwarfs in the Sun’s local neighborhood.
This visualization represents a 3D map of brown dwarfs (red dots) that have been discovered within 65 light-years of the Sun. The Sun, which is not shown, is located at the center of the view. The disk of the Milky Way appears in the background. Other stars close to the Sun appear as variously colored points in the field. Image credit: NOIRLab / NSF / AURA / J. da Silva.
Brown dwarfs are cool, dim objects that have a size between that of a gas giant planet, such as Jupiter or Saturn, and that of a Sun-like star.
Sometimes called failed stars, they are too small to sustain hydrogen fusion reactions at their cores, yet they have star-like attributes.
They have masses between 11 and 80 times that of Jupiter, and are classified spectrally into M-, L-, T- and Y-type dwarfs.
Despite their name, they are of different colors. Many brown dwarfs would likely appear magenta or orange-red to the human eye.
Their low mass, low temperature, and lack of internal nuclear reactions make them extremely faint and difficult to detect.
“Brown dwarfs are the low-mass byproducts of the process that forms stars, yet the least massive of them have many characteristics in common with exoplanets,” said Dr. J. Davy Kirkpatrick, an astronomer at Caltech/IPAC.
“They’re exoplanet laboratories, but since they are usually by themselves and lack the complications caused by a blinding host sun, they’re much easier to study.”
To help identify elusive brown dwarfs in massive datasets, the astronomers enlisted the help of the Backyard Worlds collaboration, a worldwide network of more than 100,000 citizen scientists.
They also used NASA’s Spitzer Space Telescope to observe a set of 361 local brown dwarfs of types L, T, and Y, and combined them with previous discoveries to make a 3D map of 525 brown dwarfs.
Besides the citizen science discoveries, scientists made use of CatWise, a NASA-funded catalog of objects from WISE and NEOWISE missions, to complete their census.
One of the most intriguing results of the study is that it provides more evidence that the Sun’s immediate neighborhood (within roughly 7 light-years) is rather unusual.
While most stars in the Milky Way are red dwarfs, earlier results revealed that the Sun’s closest neighbors are much more diverse, with different types of objects, from Sun-like stars to brown dwarfs, appearing in roughly equal numbers.
The new results add to this disparity by turning up no more extremely cold brown dwarfs like our close-by neighbor WISE 0855, the coldest known brown dwarf, even though the team expected to find at least several more within 65 light-years of the Sun.
This result hints at the possibility that yet more cold brown dwarfs have so far eluded detection.
“Thanks to the efforts of volunteers around the world, we have a better idea than ever of the objects in our cosmic backyard,” said co-author Dr. Aaron Meisner, an astronomer at NSF’s National Optical-Infrared Astronomy Research Laboratory.
“But we suspect that more of the Sun’s cold and close neighbors still await discovery within our vast data archives.”
A paper on the findings will be published in the Astrophysical Journal Supplement Series.
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J. Davy Kirkpatrick et al. 2021. The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs. ApJSS, in press; arXiv: 2011.11616
