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; Acknowledgement: William Pendrill
Maunakea, Hawaii – How complete is our census of
the Sun’s closest neighbors? Astronomers and a team of data-sleuthing
volunteers participating in Backyard Worlds: Planet 9,
a citizen science project, have discovered roughly 100 cool worlds near
the Sun — objects more massive than planets but lighter than stars,
known as brown dwarfs.
With the help of W. M. Keck Observatory on Maunakea in Hawaii, the
research team found several of these newly discovered worlds are among
the very coolest known, with a few approaching the temperature of Earth —
cool enough to harbor water clouds.
The study will be published in the August 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. Yet astronomers are still unearthing new residents of the
solar neighborhood. The new Backyard Worlds
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.
“These cool worlds offer the opportunity for new
insights into the formation and atmospheres of planets beyond the solar
system,” said lead author Aaron Meisner from the National Science
Foundation’s NOIRLab. “This collection of cool brown dwarfs also allows
us to accurately estimate the number of free-floating worlds roaming
interstellar space near the Sun.
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.
Artist’s impression of 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
Follow-up observations using NASA’s Spitzer Space Telescope, Mont
Mégantic Observatory, and Las Campanas Observatory also contributed to
the brown dwarf temperature estimates.
Brown dwarfs lie somewhere between the most massive planets and the
smallest stars. Lacking the mass needed to sustain nuclear reactions in
their core, brown dwarfs are sometimes referred to as “failed stars.”
Their low mass, low temperature, and lack of internal nuclear reactions
make them extremely faint — and therefore extremely difficult to detect.
Because of this, when searching for the very coolest brown dwarfs,
astronomers can only hope to detect such objects relatively close to the
Sun.
To help find our Sun’s coldest, nearest neighbors, astronomers with
the Backyard Worlds project turned to a worldwide network of more than
100,000 citizen scientists. These volunteers diligently inspect
trillions of pixels of telescope images to identify the subtle movements
of nearby brown dwarfs and planets. Despite the advances of machine
learning and supercomputers, there’s still no substitute for the human
eye when it comes to finding faint, moving objects.
Backyard Worlds volunteers have already discovered more than 1,500
stars and brown dwarfs near the Sun; this new discovery represents about
100 of the coldest in that sample. Meisner says this is a record for
any citizen science program, and 20 of the citizen scientists are listed
as co-authors of the study.
The availability of decades of astronomical catalogs through NOIRLab’s Astro Data Lab helped make the discoveries possible.
“The technical burden of downloading billion-object astronomical
catalogs is typically insurmountable for individual
investigators—including most professional astronomers,” said Meisner.
“Thankfully, the Astro Data Lab’s open and accessible web portal allowed
Backyard Worlds citizen scientists to easily query massive catalogs for
brown dwarf candidates.”
Data sets from NASA’s WISE satellite as well as archival observations
from telescopes at Cerro Tololo Inter-American Observatory and Kitt
Peak National Observatory were also key to these brown dwarf
discoveries.
“It’s exciting these could be spotted first by a citizen scientist,”
said Meisner. “The Backyard Worlds discoveries show that members of the
public can play an important role in reshaping our scientific
understanding of our solar neighborhood.”
Source: W. M. Keck Observatory
About NIRES
The Near Infrared Echellette Spectrograph (NIRES) is a prism cross-dispersed near-infrared spectrograph built at the California Institute of Technology by a team led by Chief Instrument Scientist Keith Matthews and Prof. Tom Soifer. Commissioned in 2018, NIRES covers a large wavelength range at moderate spectral resolution for use on the Keck II telescope and observes extremely faint red objects found with the Spitzer and WISE infrared space telescopes, as well as brown dwarfs, high-redshift galaxies, and quasars. Support for this technology was generously provided by the Mt. Cuba Astronomical Foundation.
About W. M. Keck Observatory
The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems.
Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
