Universe Today
Astronomers have been intrigued by a certain type of binary systems that pulse with long-period bursts of radio waves. These pulses occur every few minutes, much longer than the radio pulses from rapidly spinning neutron stars (pulsars), which repeat within seconds. Scientists have speculated that these intense beams of radio light (masers) were caused by the synchronized motion of a white dwarf and M-type red dwarf star, but questions remained about how the process worked.
In a new study, Caltech researchers used supercomputer simulations that have (for the first time) provided a clear picture of how interactions between these binary pairs power the masers they shoot into space. Specifically, the simulations detail how a known process called electron cyclotron maser instability (ECMI) causes radio bursts. Their results, published in The Astrophysical Journal Letters, offer scientists a new method for creating computational models of radio emission from binary systems with an interacting white dwarf.
The study was conducted by Yici Zhong and Elias R. Most, two researchers from the Theoretical AstroPhysics Including Relativity and Cosmology (TAPIR) group and the Walter Burke Institute for Theoretical Physics at the California Institute of Technology (Caltech). Zhong is a Sherman Fairchild Postdoctoral Scholar Research Associate in Theoretical Astrophysics while Most is an Assistant Professor of Theoretical Astrophysics and a William H. Hurt Scholar.
This artwork shows how white dwarf–M dwarf binary stars create radio emission. Credit: AI-generated artwork by Elias Most
Interestingly, radio pulses observed in white dwarf-M-type dwarf (WD-MD) systems resemble the planetary radio emissions observed between Jupiter and its innermost "Galilean" moon Io. Astronomers first noted these radio bursts in 1955 and were puzzled as to what mechanisms could be driving them. In 1969, Caltech scientists Peter Goldreich, Professor Lee A. DuBridge, and Donald Lynden-Bell solved part of that puzzle by proposing that a powerful current is generated between the two bodies as Io sweeps through Jupiter's magnetic field.
They further argued that the orbital motion produced a million-ampere flow of electric current between Io and Jupiter's magnetosphere in the shape of a tube. This prediction was later confirmed by direct satellite imaging, while other research demonstrated how these currents power the radio waves. This process came to be known as electron cyclotron maser instability (ECMI), in which electrons spiral through magnetic fields in a way that produces radio emissions.
In their study, Zhong and Most examined how this same mechanism could power radio bursts in two known WD-MD systems: GLEAM-X J0704–37 and ILT J1101+5521. The former system was previously confirmed by Caltech researcher Antonio Rodriguez (PhD '25) to be powered by ECMI. As this system's white dwarf and red dwarf orbit each other (every two hours), a powerful current is generated that fuels the ECMI. As electrons in the current become unstable relative to the ECMI, a maser is produced.
Similar to a pulsar, the maser is never turned off, but becomes visible when it crosses an observer's line of sight, creating the appearance of pulses. As Most explained:
The electrons become collectively unstable and start dancing around magnetic field lines in unison like a Viennese waltz. The results confirm that Peter Goldreich's and Donald Lynden-Bell's theory about Jupiter and Io is applicable beyond planets in our solar system. And we show that the mechanism is 10 times more efficient than was previously thought.
Further Reading: Caltech, The Astrophysical Journal Letters
