It can be difficult to detect brown dwarfs. Most of them are identified by infrared telescopes since they can emit a great deal of heat. While that works well for the warmest brown dwarfs, it doesn’t work well for cooler ones. But recently a team discovered a brown dwarf using a radio telescope, which opens the door to a new way of finding them.
Large planets such as Jupiter emit a tremendous amount of radio light. This is because they have strong magnetic dynamos. Their magnetic fields can trap charged particles, causing them to spiral toward the poles. These particles slam into the dwarf’s atmosphere near the poles, creating aurora similar to what we see on Earth. Since the charged particles are accelerated along the magnetic fields, they emit radio light.
Since brown dwarfs are similar to Jupiter, they also have aurora that emits radio. We’ve observed these radio emissions from brown dwarfs before. In this new study, a team used the low-frequency radio telescope known as LOFAR to capture the radio signal from a previously undiscovered brown dwarf. It is the first brown dwarf to be discovered purely by radio.
LOFAR is particularly well suited to discover brown dwarfs by radio since it is most sensitive at the low frequencies these bodies emit. The radio telescope can also detect the polarization of radio signals. Since radio emissions from magnetic fields are polarized, this allows LOFAR to pick out the radio signals of brown dwarfs and Jupiter-type planets more easily. With luck, LOFAR should be able to detect many more brown dwarfs in the near future.