100 cool worlds found near the sun

How complete is our census of the Sun’s closest neighbors? Astronomers and a team of data-research volunteers participating in Backyard Worlds: Planet 9, a citizen science project, have discovered around 100 cool worlds near the Sun – objects more massive than planets but lighter than stars, known under the name of brown dwarfs.

With the help of the WM Keck Observatory on Maunakea in Hawaii, the research team discovered that several of these newly discovered worlds are among the coldest known, with a few approaching Earth’s temperature – sufficiently cool to shelter water clouds.

The study will be published in the August 20, 2020 issue of Astrophysics Journal and is available in preprinted format at arXiv.org.

The discovery and characterization of astronomical objects near the Sun is fundamental to our understanding of our place and the history of the universe. Yet astronomers are always on the lookout for new residents of the solar district. Backyard Worlds’ new discovery fills a previously empty gap in the range of low-temperature brown dwarfs, identifying a long-sought missing link in the brown dwarf population.

“These cold worlds provide the opportunity for new knowledge about the formation and atmospheres of planets beyond the solar system,” said lead author Aaron Meisner of the National Science Foundation’s NOIRLab. “This collection of cold 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 palest and freshest brown dwarfs recently discovered, physics professor Adam Burgasser of UC San Diego and researchers at the Cool Star Lab used the sensitive instrument of the NIR Scale Near Infrared Spectrometer. Keck observatory, or NIRES.

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

Follow-up observations using NASA’s Spitzer Space Telescope, Mont Mégantic Observatory and Las Campanas Observatory also contributed to the temperature estimates for the Brown Dwarf.

Brown dwarfs fall somewhere between the most massive planets and the smallest stars. Lacking the mass to support nuclear reactions in their nucleus, brown dwarfs are sometimes referred to as “failing stars”. Their low mass, low temperature and the absence of internal nuclear reactions make them extremely weak and therefore extremely difficult to detect. For this reason, when looking for the cooler brown dwarfs, astronomers can only hope to detect such objects relatively close to the Sun.

To help find the coldest and closest neighbors to our Sun, astronomers from the Backyard Worlds project turned to a global network of more than 100,000 citizen scientists. These volunteers assiduously inspect billions of pixels of telescope images to identify the subtle movements of brown dwarfs and nearby planets. Despite advances in machine learning and supercomputers, there is still no substitute for the human eye when it comes to finding weak and moving objects.

Backyard Worlds volunteers have already discovered more than 1,500 brown stars and dwarfs near the Sun; this new finding represents about 100 of the coldest in this 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 via NOIRLab’s Astro Data Lab has helped make the discoveries possible.

“The technical burden of downloading astronomical catalogs of billions of objects is generally insurmountable for individual researchers, including most professional astronomers,” Meisner said. Fortunately, the Astro Data Lab’s open and accessible web portal made it easy for Backyard Worlds citizen scientists to query massive catalogs for Brown Dwarf candidates.

Data sets from NASA’s WISE satellite as well as archival observations from the telescopes at the Cerro Tololo Inter-American Observatory and the Kitt Peak National Observatory were also critical to these brown dwarf finds.

“It’s exciting that these can be spotted first by a citizen scientist,” Meisner said. “The findings from Backyard Worlds show that members of the public can play an important role in reshaping our scientific understanding of our solar neighborhood.”