NSF–DOE Rubin Observatory Will Detect Thousands of Elusive Brown Dwarfs, Unlocking Milky Way Mysteries

One could argue that brown dwarfs don’t get the love they deserve. Sometimes referred to as ‘failed stars’, they don’t have enough mass to sustain nuclear fusion, which powers all stars, including our Sun. But they are also too big to be considered planets, with some having 75 times the mass of Jupiter. Despite not fitting neatly into one of these familiar categories of astronomical objects, brown dwarfs hold important clues to the processes that formed the Milky Way. NSF–DOE Vera C. Rubin Observatory, jointly funded by the U.S. National Science Foundation (NSF) and the U.S. Department of Energy, Office of Science (DOE/SC), will soon reveal a never-before-seen population of brown dwarfs beyond the Sun’s local neighborhood, giving scientists more tools to map the history and evolution of our home galaxy.

Rubin Observatory is a Program of NSF NOIRLab, which, along with SLAC National Accelerator Laboratory, will jointly operate Rubin.

“Brown dwarfs are these weird, intermediate objects that defy classification,” said Aaron Meisner, Associate Astronomer at NSF NOIRLab and a member of Rubin Observatory’s Community Science Team. In addition to being smaller than stars, brown dwarfs are much cooler, with surface temperatures ranging from about 0 to 2000 degrees Celsius (32 to 3600 degrees Fahrenheit). That means they don't produce very much light in the visible spectrum, which makes them difficult to detect with optical telescopes. “It’s possible we’re swimming in a whole sea of these objects that are really faint and hard to see,” said Meisner.

The same qualities that make brown dwarfs unusual and elusive also make them excellent candidates for helping scientists disentangle the Milky Way's formation and evolution, which was strongly influenced by mergers with smaller, nearby galaxies. Brown dwarfs have longer life spans than the larger, hotter stars, so brown dwarfs that formed in the early Universe are still out there, largely unchanged and containing valuable information about the Milky Way's early history. By studying the properties of ancient brown dwarfs, scientists can trace them to their original galaxies that merged with the Milky Way and thereby reveal changes in how Milky Way stars formed over time.

For ten years, beginning in late 2025, Rubin’s Simonyi Survey Telescope will scan the sky from its vantage point on Cerro Pachón in Chile. Rubin will take wide, detailed images using the LSST Camera — the largest digital camera in the world — and covering the entire visible sky every few nights. Rubin’s six camera filters will transmit light from a broad range of optical wavelengths, and into the near-infrared. Rubin’s near-infrared capability, combined with its wide field of view and ability to see deep into space, will make it a powerful detector of faint objects that emit mainly infrared light, like brown dwarfs. Detailed predictions of the distant brown dwarfs Rubin will see have recently been performed by Christian Aganze, a postdoctoral researcher at Stanford University.

Rubin will capture the light from brown dwarfs at far greater distances than previous visible light surveys. Existing optical surveys like Pan-STARRS and Sloan Digital Sky Survey have mainly helped us discover brown dwarfs that are relatively close by. “Current surveys go to a distance of about 150 light-years from the Sun for ancient brown dwarfs in the Milky Way’s halo,” said Meisner. “But Rubin will be able to see more than three times farther than that.” This increase in distance means an even bigger increase in the total volume of space available for scientists to find and study these brown dwarfs — offering scientists the larger sample of these faint objects they’ve ever had. 

Researchers like Meisner are excited at the prospect of finding enough distant brown dwarfs to study on a population level instead of individually, so they can compare the properties of different subgroups and look for patterns in the way they’re distributed.

“Rubin will reveal a population of ancient brown dwarfs about 20 times bigger than what we’ve seen up to now,” said Meisner. “That will allow us to decipher which pieces of Galactic substructure different brown dwarfs came from, and lead to major advances in our understanding of how the Milky Way’s populations formed.”

More Information

The NSF–DOE Rubin Observatory is a joint initiative of the U.S. National Science Foundation (NSF) and the Department of Energy (DOE). Its primary mission is to carry out the Legacy Survey of Space and Time, providing an unprecedented data set for scientific research supported by both agencies. Rubin is operated jointly by NSF NOIRLab and SLAC National Accelerator Laboratory (SLAC). NOIRLab is managed for NSF by the Association of Universities for Research in Astronomy (AURA) and SLAC is operated for DOE by Stanford University. France provides key support to the construction and operations of Rubin Observatory through contributions from CNRS/IN2P3. Additional contributions from a number of international organizations and teams are acknowledged.

The U.S. National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.

NSF NOIRLab (U.S. National Science Foundation National Optical-Infrared Astronomy Research Laboratory), the U.S. center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.

SLAC National Accelerator Laboratory is a vibrant multiprogram laboratory that explores how the Universe works at the biggest, smallest, and fastest scales and invents powerful tools used by scientists around the globe. With research spanning particle physics, astrophysics and cosmology, materials, chemistry, bio- and energy sciences and scientific computing, SLAC helps solve real-world problems and advance the interests of the nation.

SLAC is operated by Stanford University for the U.S. Department of Energy’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time.

Links

• Vera C. Rubin Observatory website
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