Important discovery of a cold brown dwarf

Astronomers have reported the first direct discovery of a cold brown dwarf from its radio wavelength emission. 

It’s a significant breakthrough, as it demonstrates that it is possible to detect objects that are too cold and faint to be found in existing infrared and optical surveys. And that may include large, free-floating exoplanets.

BDR J1750+3809, as it has been designated, was found thanks to a collaboration between Europe’s LOFAR (LOw Frequency Array) telescope and the Gemini North telescope and NASA InfraRed Telescope Facility (IRTF) in Hawaii.

Brown dwarfs are substellar objects straddling the boundary between the largest planets and the smallest stars. The first unambiguous observation did not occur until 1995. 

Sometimes dubbed failed stars, they lack the mass to trigger hydrogen fusion in their cores, instead glowing at infrared wavelengths with leftover heat from their formation. While they lack the fusion reactions that keep the Sun shining, they can emit light at radio wavelengths. 

The underlying process powering this radio emission is familiar, as it occurs in Jupiter. The planet’s powerful magnetic field accelerates charged particles such as electrons, which in turn produces radiation.

Radio emissions have previously been detected from only a handful of cold brown dwarfs, and these had already been catalogued by infrared surveys. 

In the new work, the team first used a sensitive radio telescope to discover cold, faint sources, then made follow-up infrared observations with a large telescope to categorise them.

“In this discovery, Gemini was particularly important because it identified the object as a brown dwarf and also gave us an indication of the temperature of the object,” says Harish Vedantham from the Netherlands Institute for Radio Astronomy, lead author of a paper in The Astrophysical Journal Letters.

“The Gemini observations told us that the object was cold enough for methane to form in its atmosphere, showing us that the object is a close cousin of Solar System planets like Jupiter.” 

The ultimate goal, Vedantham says, is to understand magnetism in exoplanets and how it impacts their ability to host life.

“Because magnetic phenomena of cold brown dwarfs are so similar to what is seen in Solar System planets, we expect our work to provide vital data to test theoretical models that predict the magnetic fields of exoplanets.”