Some pairs of stars could produce long radio pulses through a mechanism similar to the one connecting Jupiter to its moon Io.
Astronomers are seeking to explain radio sources that light up at very long intervals, sometimes every few dozen minutes or several hours. Two objects observed in our Galaxy, GLEAM-X J0704-37 and ILT J1101+5521, are associated with pairs of stars. Each consists of a white dwarf and a small red star.
Diagram of a synchronously rotating white dwarf–red dwarf binary system (WD-MD).
The blue curves represent magnetic field lines. The ECM emission region (orange) near the white dwarf’s pole produces a radio beam (yellow) directed toward the observer.
A white dwarf is the very dense core left behind by a star comparable to the Sun after the end of its active life. Its companion, called a red dwarf, is a smaller and less massive star. In the systems studied, the two bodies orbit each other. This dance brings their magnetic environments into regular interaction.
The researchers simulated the behavior of charged particles surrounding these stars. Their results show that a powerful magnetic field can accelerate and organize electrons in a way that produces coherent radio waves. This mechanism is known as electron cyclotron maser emission. It can strongly concentrate the emission in certain directions and at certain frequencies.
A comparable phenomenon already operates in the Solar System. Io moves through Jupiter’s immense magnetic environment and disturbs the charged particles found there. This interaction helps produce strong radio emissions. In a stellar pair, the red dwarf could play a similar role in the face of the white dwarf’s magnetic field.
The simulations also show that the resulting radiation can be partially polarized. Polarization describes the orientation of the radio wave’s oscillations. This characteristic matters here because both observed astronomical sources exhibit polarized emission. The model therefore reproduces several expected properties without requiring an entirely new mechanism.
The next step is to connect these simulations more precisely with radio telescope measurements. The researchers particularly want to study how the composition of the medium and the geometry of the magnetic fields alter the shape, frequency, and polarization of the pulses. These signatures could make it possible to identify this mechanism among the various long-period radio sources.