Since their discovery in 2022, slowly repeating bursts of intense radio waves from deep space have captivated and baffled astronomers. These enigmatic signals, pulsating at intervals far longer than typical celestial radio sources, defied explanation. Now, groundbreaking research has successfully traced one of these pulsating signals to its origin: a surprisingly common red dwarf star, most likely locked in a binary orbit with a white dwarf – the collapsed core of a star that exploded long ago.
The mystery began in 2022 with the detection of periodic radio pulsations repeating every 18 minutes. These pulses dramatically outshone their surroundings, shining brightly for three months before mysteriously vanishing. While some repeating radio signals originate from neutron stars known as radio pulsars – rapidly spinning objects beaming radio waves like cosmic lighthouses – the 18-minute cycle presented a significant challenge. Existing theories suggest a pulsar rotating that slowly shouldn’t produce detectable radio waves. This anomaly hinted at the possibility of revolutionary discoveries in physics or a critical gap in our understanding of pulsar radiation mechanisms, a field with a half-century of unanswered questions.
Further fueling the intrigue, more slowly blinking radio sources – dubbed ‘long-period radio transients’ – were subsequently identified, bringing the known count to around ten. However, simply finding more examples didn’t provide the answers. The initial sources were all located deep within the crowded Milky Way’s center, making it impossible to identify the specific star or object emitting the signals. The sheer density of stars in this region meant that any one of thousands could be responsible, or none at all.
To overcome this challenge, researchers embarked on a systematic sky survey using the Murchison Widefield Array (MWA) radio telescope in Western Australia. The MWA’s impressive ability to observe a vast 1,000 square degrees of sky per minute proved crucial. Csanád Horváth, an undergraduate student at Curtin University, meticulously processed data covering half the sky, focusing on less densely populated regions of the Milky Way, searching for these elusive signals.
This painstaking effort yielded success, revealing a new source, designated GLEAM-X J0704-37. This source produced minute-long pulses of radio waves, echoing the behavior of other long-period radio transients. However, its pulse repetition was significantly slower, occurring only once every 2.9 hours, making it the slowest long-period radio transient discovered to date.
Follow-up observations using the MeerKAT telescope in South Africa – the Southern Hemisphere’s most sensitive radio telescope – precisely pinpointed the origin of the radio waves: a red dwarf star. Red dwarfs, while constituting 70% of the Milky Way’s stars, are incredibly faint, invisible to the naked eye. By combining historical MWA data and new MeerKAT observations, researchers noticed a subtle variation in pulse arrival times, suggesting the radio emitter wasn’t the red dwarf itself, but an unseen companion in a binary orbit.
Based on stellar evolution models, this invisible emitter is most likely a white dwarf. A neutron star or black hole would have resulted in an explosion so powerful that it would likely disrupt the binary orbit. The scenario involves a red dwarf star, similar to our Sun but far smaller and cooler, emitting a stellar wind of charged particles. This wind interacts with the powerful magnetic field of the orbiting white dwarf, causing the particles to accelerate and generate the observed radio waves. This process bears resemblance to how the Sun’s solar wind interacts with Earth’s magnetic field to create auroras and low-frequency radio waves.
While similar systems exist, such as AR Scorpii, none exhibit the brightness or slow pulse rate of the long-period radio transients. Further research, focused on the discovery and study of additional systems, is critical to determining whether a single physical model can account for all these phenomena, or if multiple types of systems are capable of producing long-period radio pulsations. Regardless, this discovery highlights the importance of remaining open to unexpected findings and underscores the ongoing quest to unravel the universe’s many cosmic mysteries.
