Our sun may not be so alone after all. Astronomers have discovered neighboring 95 brown dwarfs, often referred to as failed stars, within a few dozen light-years of our sun.
Members of the public collaborated with astronomers to help identify these cool worlds that are too massive to be planets and too small to be stars. The brown dwarfs don’t have quite enough mass to sustain nuclear reactions in their core that power stars, so they’re more like cooling embers, according to researchers at the National Science Foundation’s NOIRLab.
The discoveries were made through the Backyard Worlds: Planet 9 project, a NASA-funded collaboration that brings professional astronomers together with volunteers called citizen scientists. Backyard Worlds includes data gathered by NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer, or NEOWISE, satellite and its previous iteration, WISE, which observed the sky between 2010 and 2011.
While these brown dwarfs aren’t located in our solar system, they range between 23 to 60 light-years from the sun and far enough away from its heat that they remain quite cool.
These are some of the coldest known brown dwarfs ever discovered, including a few that are even similar to the average temperature of Earth. Those brown dwarfs could even have water clouds.
“These cool worlds offer the opportunity for new insights into the formation and atmospheres of planets beyond the Solar System,” said Aaron Meisner, lead study author and assistant scientist at NOIRLab, said in a statement. “This collection of cool brown dwarfs also allows us to accurately estimate the number of free-floating worlds roaming interstellar space near the Sun.”
The study is available as a preprint and will publish this week in The Astrophysical Journal.
The search for new worlds
The Backyard Worlds project includes more than 100,000 citizen scientists from across the globe. About 20 citizen scientists from 10 countries are coauthors on the new study. They worked with astronomers to study the pixels of telescope images to identify brown dwarfs.
Although software and algorithms can help spot these objects and exoplanets, relying on humans to spot these signatures can provide the most promising results.
In addition to sky maps from WISE and NEOWISE, data from the National Science Foundation’s NOIRLab and NASA’s retired Spitzer Space Telescope were also used during the project.
“Vast modern datasets can unlock landmark discoveries, and it’s exciting that these could be spotted first by citizen scientists,” Meisner said. “These Backyard Worlds discoveries show that members of the public can play an important role in reshaping our scientific understanding of our solar neighborhood.”
Previously, Backyard Worlds citizen scientists have helped find more than 1,500 cold worlds in the vicinity of the sun, but this latest discovery is the largest published study of brown dwarfs found through citizen science.
“It’s awesome to know that our discoveries are now counted among the Sun’s neighbors and will be targets of further research,” said Jim Walla, study coauthor, citizen scientist and Astro Data Lab user.
NOIRLab’s Astro Data Lab science platform provided an accessible way for citizen scientists to search massive astronomical catalogs filled with a billion objects. And archival data from National Science Foundation programs including the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory in Arizona and the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile helped make the discoveries possible.
Future telescopes and observatories, like the Vera C. Rubin Observatory, under construction in Chile, and the James Webb Space Telescope due to launch in October 2021, will also provide new data for future projects.
The magenta-colored or sometimes reddish worlds can typically reach thousands of degrees Fahrenheit, but the newly discovered brown dwarfs are much cooler. Scientists believe that brown dwarfs cool with age.
Their temperature also means they are smaller and fainter in visible light, but they still emit heat in infrared light. That light can be seen by NEOWISE or the retired NASA Spitzer Space Telescope, which helped make brown dwarf discoveries during its 16-year operation between 2003 and 2019.
Searching for cool brown dwarfs has been incredibly difficult, but their proximity to the sun makes it a little easier.
These cool brown dwarfs act as a missing link among previously observed brown dwarfs.
The coldest-known brown dwarf was observed in 2014, called WISE 0855, using NASA’s WISE mission. With a temperature of minus 10 degrees Fahrenheit, the brown dwarf was actually thought to be a rogue exoplanet because it didn’t come close to that of other brown dwarfs.
“Our new discoveries help connect the dots between 0855 and the other known brown dwarfs,” said astrophysicist Marc Kuchner, the principal investigator of Backyard Worlds and the Citizen Science Officer for NASA’s Science Mission Directorate, in a statement.
Investigating brown dwarfs, especially those in the same part of the cosmic neighborhood as our sun, helps astronomers understand more about our place in the universe and offers a glimpse into worlds outside of our solar system.
“This paper is evidence that the solar neighborhood is still uncharted territory and citizen scientists are excellent astronomical cartographers,” said astronomer Jackie Faherty, study coauthor at the American Museum of Natural History in New York, in a statement. “Mapping the coldest brown dwarfs down to the lowest masses gives us key insights into the low-mass star-formation process while providing a target list for detailed studies of the atmospheres of Jupiter analogs.”
There is no question that the hands-on participation of citizen scientists worldwide, and the availability of data from telescopes and observatories, will continue to move forward our understanding of our world and beyond.