100 Cool Worlds Found Near the Sun

Artist’s impression of one of this study’s superlative discoveries, the oldest known wide separation white dwarf plus cold brown dwarf pair. The small white orb represents the white dwarf (the remnant of a long-dead Sun-like star), while the brown/orange foreground object is the newly discovered brown dwarf companion. This faint brown dwarf was previously overlooked until it was spotted by citizen scientists because it lies right within the plane of the Milky Way. Credit: NOIRLab/NSF/AURA/P. Marenfeld; acknowledgment: William Pendrill

With the help of citizen scientists, astrophysicists have discovered about 100 cool worlds in the Sun’s neighborhood. They’re brown dwarfs, sometimes referred to as “failed stars,” which are objects that are more massive than planets but lighter than stars.

The citizen scientists who made the discovery are data-sleuthing volunteers participating in Backyard Worlds: Planet 9, a citizen science project. Their discovery bridges a previously empty gap in the range of low-temperature brown dwarfs, identifying a long-sought missing link within the brown dwarf population.

Follow-up observations, including data from W.M. Keck Observatory on Maunakea in Hawai‘i, reveal some of them are among the coolest brown dwarfs ever discovered with temperatures nearly as cool as Earth’s – cool enough to harbor water clouds.

These free-floating worlds are located just 23-60 light-years away from the Sun.

The study will be published in the Aug. 20, 2020 issue of The Astrophysical Journal and is available in preprint format on arXiv.org.

“Discovering and characterizing astronomical objects near the Sun is fundamental to our understanding of our place in, and the history of, the universe,” a press release from W.M. Keck Observatory stated. “Yet astronomers are still unearthing new residents of the solar neighborhood.”

To identify several of the faintest and coolest of the newly discovered brown dwarfs, UC San Diego’s Professor of Physics Adam Burgasser and researchers from the Cool Star Lab used Keck Observatory’s sensitive Near-Infrared Echellette Spectrometer, or NIRES, instrument.

“We used the NIRES spectra to measure the temperature and gases present in their atmospheres. Each spectrum is essentially a fingerprint that allows us to distinguish a cool brown dwarf from other kinds of stars,” said Burgasser, a co-author of the study.

These cool worlds, lead author Aaron Meisner from the National Science Foundation’s NOIRLab said, offer the opportunity for new insights into the formation and atmospheres of planets beyond the solar system.

“This collection of cool brown dwarfs also allows us to accurately estimate the number of free-floating worlds roaming interstellar space near the Sun,” Meisner said.