For the first time, astronomers have used observations from a radio telescope and a pair of observatories on Maunakea to discover and characterize a cold brown dwarf, also known as a “super planet” or “failing star.”
The discovery, designated BDR J1750 + 3809, is the first subcellular object detected by radio observations – so far brown dwarfs have largely been found from infrared surveys of the sky.
The BDR J1750 + 3809 (nicknamed “Elegast” by the discovery team) was first identified using data from the Low-Frequency Array Telescope (LOFAR) in Europe, then confirmed using telescopes at Maunakea summit, namely the International Gemini Observatory and the NASA Infrared Telescope Facility (which is operated by the University of Hawaii). The direct discovery of these objects with sensitive radio telescopes such as LOFAR is a significant breakthrough, as it demonstrates that astronomers can detect objects that are too cold and too faint to be found in infrared readings, and possibly even detect giant exoplanets. floating carbonated.
The research is published in Letters from the astrophysical journal. Astronomer Michael Liu and graduate student Zhoujian Zhang from the UH Institute of Astronomy (IfA) co-authored the article. “This work opens up a whole new method for finding the coldest objects floating near the Sun, which would otherwise be too faint to be discovered with the methods used for 25 years,” Liu said.
Brown dwarfs in a new light
Brown dwarfs straddle the border between larger planets and smaller stars. Sometimes dubbed “failing stars,” brown dwarfs lack the mass to trigger the fusion of hydrogen in their nucleus, and instead, they glow at infrared wavelengths with the waste heat from their formation. Also known as “super planets,” brown dwarfs have gaseous atmospheres that look more like giant gas planets in our solar system than any star.
While brown dwarfs don’t have the fusion reactions that make the sun glow, they can emit light at radio wavelengths. The underlying process fueling this radio show is familiar, as it also occurs in the largest planet in the solar system. Jupiter’s powerful magnetic field accelerates charged particles such as electrons, which in turn produce radiation – in this case radio waves and auroras.
The fact that brown dwarfs are radio transmitters allowed the international collaboration of astronomers behind this result to develop a new observation strategy. Radio broadcasts had previously been detected from a handful of cold brown dwarfs, which were discovered and cataloged by infrared surveys before being observed with radio telescopes. The team decided to reverse this strategy, using a sensitive radio telescope to discover cold and weak radio sources, and then perform follow-up infrared observations with Maunakea telescopes to categorize them.
“We asked ourselves: ‘Why point our radio telescope at cataloged brown dwarfs? Said Harish Vedantham, lead author of the study and astronomer at ASTRON in the Netherlands. “Let’s just make a big picture of the sky and find these objects right in the radio.”
As well as being an exciting result in itself, the discovery of the BDR J1750 + 3809 could provide a tantalizing glimpse into a future where astronomers can measure the properties of the magnetic fields of exoplanets. Cool brown dwarfs are the closest things to exoplanets that astronomers can currently detect with radio telescopes, and this finding could be used to test theories predicting the strength of exoplanets’ magnetic fields. Magnetic fields are an important factor in determining atmospheric properties and the long-term evolution of exoplanets.
The technique could give other results
Having found a variety of telltale radio signatures in their observations, the team had to distinguish potentially interesting sources from background galaxies. To do this, they looked for a special form of circularly polarized radio waves – a feature of light from stars, planets, and brown dwarfs, but not background galaxies. After finding a circularly polarized radio source, the team then turned to archival footage, the Gemini-North Telescope, and NASA’s IRTF to provide the measurements needed to identify their discovery.
NASA IRTF is equipped with a sensitive spectrometer, SpeX, which has been a workhorse for the study of brown dwarfs for the past 20 years, including an upgrade five years ago funded by National Science Foundation. The team used SpeX to obtain a spectrum of BDR J1750 + 3809, which revealed the characteristic signature of methane in the atmosphere. Methane is the hallmark of the cooler brown dwarfs, and also abundant in the atmospheres of the gas giant planets of our solar system.
“These observations really highlight the increased efficiency of SpeX following its NSF-funded upgrade with infrared arrays and advanced electronics in 2015,” said John Rayner, director of the IRTF and astronomer at UH IfA.
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