Brown dwarfs form like stars, but are not massive enough to ignite nuclear fusion of hydrogen within their cores -- a defining mechanism within proper stars -- yet are too massive to be called planets.
They are typically characterised by how bright they are at different wavelengths, which can be measured either through photometry, that provides their colours, or through spectroscopy, that reveals their spectrum, a measurement of brightness across a wavelength range. The colors and spectrum inform astrophysicists about the atmospheric composition of the object.
"These two newly discovered brown dwarfs have colours and spectra unlike anything we've ever seen before," says astronomer and research scientist Adam Schneider of Arizona State University. "And citizen scientists had a huge role in their discoveries."
Based on current models, these brown dwarfs are likely some of the oldest ever detected. Because the interstellar environment was different back when these brown dwarfs formed, they still retain an unusual chemical composition that is observed by the scientists. Further, both of these brown dwarfs are extremely heavy, so much so that they only lacked a small amount of mass to have actually become stars instead of brown dwarfs back when they were born.
Schneider is the lead author of a recently accepted article in the Astrophysical Journal detailing these discoveries and the potential implications.
Schneider first noticed one of the unusual brown dwarfs (WISEA J181006.18−101000.5, or WISE 1810 for short)) a few years ago, but it was located in a crowded area of the sky and its existence was difficult to confirm.
With the help of a tool called "WiseView" created by citizen scientist Dan Caselden, Schneider was able to confirm that the object he had seen was moving, which is a good indication that a celestial body, like a planet or brown dwarf, is near the Earth. "WiseView scrolls through data like a short movie," says Schneider, "so you can more easily see if something is moving or not." Another citizen-scientist named Arttu Sainio also identified the object as interesting, independently.
The second unusual brown dwarf (WISEA J041451.67−585456.7, or WISE 0414 for short) was discovered independently by citizen scientists -- Paul Beaulieu, Sam Goodman, William Pendrill, and Austin Rothermich -- who participate in a NASA-funded citizen scientist project called Backyard Worlds: Planet 9, as do Caselden and Sainio.
This initiative provides a platform for citizen scientists to search for new objects on the edges of our Solar System using data from NASA's Wide-field Infrared Survey Explorer (WISE) mission, which has been imaging the entire sky in infrared light. The citizen scientists who found WISE 0414 combed through hundreds of images taken by WISE, looking for movement that can best be detected with the human eye.
"The discovery of these two brown dwarfs shows that science enthusiasts can contribute to the scientific process," says Schneider. "Through Backyard Worlds, thousands of people can work together to find unusual objects in the solar neighborhood."
Once the objects were discovered by the citizen scientists, astronomers then used near-infrared spectroscopy to determine their physical properties and confirm that they are indeed brown dwarfs.
Jonathan Gagné, a former Institute for research on exoplanets at Université de Montréal Banting postdoctoral researcher who is now a scientific advisor at the Rio Tinto Alcan Planetarium, is a scientific member of the Backyard Worlds: Planet 9 project. He analyzed the spectroscopic data of the second brown dwarf, which were taken at the Baade Magellan Telescope at the Las Campanas Observatory in Chile.
"I was really surprised when I first saw the results," he recalls. "I had to repeat the analysis a few times over, using different calibrations, to convince myself there were no mistakes. The light properties of this brown dwarf were unlike anything I had ever seen, and really different from that of other known brown dwarfs."
With the discovery of these two unusual brown dwarfs, astronomers may now be able to find more of these objects in the future.
"If we just look for brown dwarfs based on previously known brown dwarf colours, we could miss these sorts of interesting objects with unusual properties," says Schneider. "These new objects will help us define a new parameter space for brown dwarf discoveries."
About this study
"WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5: The First Extreme T-type Subdwarfs?" was accepted for publication in The Astrophysical Journal. In addition to Jonathan Gagné (iREx, Université de Montréal, Space for Life), the research team includes first author Adam Schneider, an Assistant Research Scientist at Arizona State University's School of Earth and Space Exploration, 21 other co-authors from The Backyard Worlds: Planet 9 Collaboration.
The authors acknowledge funding from the NASA Astrophysics Data Analysis Program grant NNH17AE751
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