Astronomers spot cold brown dwarf with a radio telescope, a first
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| Scientists have previously observed radio signals from distant brown dwarfs, but only after finding the super planets using infrared surveys |
For the first time, researchers have used a radio telescope to identify and characterize a cold brown dwarf, or super planet. Until now, astronomers mostly relied on infrared sky surveys to find brown dwarfs, or failed stars.
The spectral signature of the super planet BDR J1750+3809 -- described Monday in The Astrophysical Journal Letters -- was identified among data collected by the Low-Frequency Array telescope, LOFAR, at the Mauna Kea Observatories, operated by the University of Hawaii.
"This work opens a whole new method to finding the coldest objects floating in the sun's vicinity, which would otherwise be too faint to discover with the methods used for the past 25 years," study co-author Michael Liu, astronomer at the University of Hawaii, said in a news release.
As their nicknames suggest, brown dwarfs straddle the line between biggest planets and smallest stars. Though not quite massive enough to sustain nuclear fusion, brown dwarfs do emit radio waves.
Like Jupiter and other gas giants, brown dwarfs and their large gaseous atmospheres host powerful magnetic fields capable of accelerating charged particles, or ions. These high-energy particles emit radio waves and fuel other electromagnetic phenomena like aurorae.
Scientists have previously observed radio signals from distant brown dwarfs, but only after finding the super planets using infrared surveys.
For the latest study, astronomers reversed the strategy, using LOFAR data to locate the brown dwarf and infrared telescopes at Mauna Kea to render the objects in greater detail.
"We asked ourselves, 'Why point our radio telescope at cataloged brown dwarfs?'" said lead author Harish Vedantham, astronomer at ASTRON in the Netherlands. "Let's just make a large image of the sky and discover these objects directly in the radio."
To differentiate brown dwarf emissions from the background emissions of distant galaxies, researchers keyed in on radio waves that were circularly polarized, a feature unique to stars, planets and brown dwarfs.
After locating a faint signal of polarized radio waves among the LOFAR data, researchers turned to archival observations from other observatories, including Gemini-North Telescope and the NASA Infrared Telescope Facility, or IRTF, to confirm their discovery.
Readings from NASA IRTF's super-sensitive spectrometer, SpeX, allowed scientists to identify methane in the distant object's atmosphere -- a telltale brown dwarf characteristic.
"These observations really highlight the increased efficiency of SpeX following its NSF-funded upgrade with state-of-the-art infrared arrays and electronics in 2015," said John Rayner, director of NASA's Infrared Telescope Facility and an astronomer at the University of Hawaii.