While not all today’s news comes to you from radio telescopes, most of it comes from radio telescopes. These giant dishes can conveniently work day or night, and thanks to our ability to easily combine multiple telescopes of data into a sprawling virtual telescope, they allow the highest resolution images of our universe. 

We take advantage of radio dishes to do everything from imaging distance supermassive black holes to watching aurorae flicker in the atmosphere of Jupiter. While we’ve known for some time that giant planets and small stars can warmly emit radio waves, discovering these kinds of objects has generally be left to the infrared observatories, with radio telescopes stepping in to do the followup work. 

As you may have noticed, we’re currently short on infrared observatories, with Spitzer retired and JWST not yet launched. And while infrared and even optical telescopes can spot warm brown dwarfs and planets, cold ones will generally be too faint to be seen – and cold lone objects might be some of the more interesting objects out there.

In a new radio survey, the LOFAR radio array was used to search for objects too cold and faint to be found in existing infrared surveys. Objects found in this survey could then be observed with large scopes like Gemini or IRTF and identified. 

One such pinprick of radio light came from an object designated BDR J1750+3809 but dubbed Elegast by the LOFAR team. This is the first non-extragalactic object to be discovered in the radio, and it was determined to be a brown dwarf star. The way they did this is actually kind of cool. 

Light from an individual star or planet will have a specific polarization – this is a fancy way of saying the light waves are oriented in a measurable way. Galaxies, which are made of many different objects with light oriented in many different ways, don’t have the same kind of polarization. To separate the distant galaxies radio scopes are so good at detecting from nearby tiny objects they aren’t generally used to detect, the research team looked for objects with polarized light.

According to team member Joe Callingham: With LOFAR, we want to go down the mass-ladder all the way to Jupiter-like planets that are too faint to have been found in existing infrared surveys, so we decided to search for these objects directly in our radio images.

This work appears in the Astrophysical Journal. In looking at the object with multiple scopes, they determined it is consistent in makeup with our system’s gas giant, Jupiter. According to co-author Harish Vedantham: 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.

This is a new technique being used to do new and awesome things, and I, for one, look forward to seeing what can be discovered in this long wavelength of light.

More Information

NOIRLab press release 

ASTRON press release 

The University of Hawaii at Manoa press release 

“Direct Radio Discovery of a Cold Brown Dwarf,” H. K. Vedantham et al., 2020 Nov. 9, Astrophysical Journal Letters (preprint on arxiv.org)