Mysterious, intermittent transmissions of high-energy radio signals emanating from a residential property have confounded astronomers since their detection in 2022.
Scientists have successfully tracked a pulsating indicator back to its source: a typical type of lightweight star called a red dwarf, likely in a binary orbit with a white dwarf, which is the core of another star that exploded long ago.
A Slowly Pulsing Thriller
In 2022, our team accomplished significant milestones. Fascinating periodic radio pulsations, recurring every 18 minutes and originating from a seemingly innocuous household location. Pulses burst forth, momentarily eclipsing everything around them, before vanishing into nothingness.
Some radio signals are known to emanate from a specific type of neutron star called a radio pulsar, characterized by its rapid spin (typically once every second or faster) and subsequent emission of radio waves in the form of a directional beam, much like a lighthouse beacon. According to current theoretical frameworks, a pulsar that spins at an interval of just 18 minutes should emit radio waves.
We initially believed that our 2022 finding could unlock new and exciting physical principles or shed light on the long-standing mystery surrounding pulsars’ radiation emission mechanisms, a puzzle that has persisted despite 50 years of dedicated research.
Astronomers have observed a plethora of faintly pulsating radio sources to emerge gradually over the past few decades. Currently, around 10 long-period radio transients have been identified.
Despite the discovery of more information, the mystery remains unsolved.
Beyond the Cosmic Fringe
Until now, all considered discoveries have been found at the very centre of the Milky Way galaxy, nestled deep within its coronary heart.
Determining the origin of radio waves is rendered extremely arduous due to the overwhelming number of stars densely packed within a limited area. It’s unclear which, if any, of these options is accountable for the sign; or perhaps none of them are to blame.
We launched a comprehensive marketing campaign to leverage our radio telescope in Western Australia, which has the potential to scan a vast area of approximately 1,000 square kilometres. The ever-changing canvas of the atmosphere, with levels of the sky shifting every minute? Curtin University student Csanád Horváth, an undergraduate scholar, ventured into the vast expanse, processing data that concealed half of the celestial canvas, seeking faint signals from sparsely inhabited regions within the Milky Way’s bounds?
And with great certainty, we’ve unearthed a fresh and ample supply! Dubbed GLEAM-X J0704-37, this enigmatic object emits minute-long pulses of radio waves, reminiscent of long-period radio transients that defy easy categorization. Notwithstanding this, the pulses recur exclusively every 2.9 hours, rendering it the slowest recorded long-period radio transient to date.
What’s the Origin of Those Radio Signals?
We conducted follow-up observations at the MeerKAT radio telescope in South Africa, renowned for being one of the most sensitive and delicate instruments in the southern hemisphere. The precise location pinpointed by these signals is that of a crimson dwarf star. While these diminutive stars account for 70% of all celestial bodies in the Milky Way, their lack of luminosity renders them invisible to the naked eye.
By integrating historical data from the Murchison Widefield Array with real-time insights gleaned from MeerKAT’s monitoring capabilities, our research revealed that pulses exhibit slight temporal variations within a repeating pattern. This is likely indicative that the radio emitter does not originate from the crimson dwarf itself, but rather from an unknown object in a binary orbit with it.
Following established astrophysical knowledge, it appears highly likely that this enigmatic radio source is actually a white dwarf, a natural terminus for small-to-medium-mass stars similar to our own sun. Had the original explosion that formed either a neutron star or black hole been as massive as to create such an extreme celestial body, it would inevitably have perturbed the orbit, rendering the current state of the system implausible.
It Takes Two to Tango
As magnetic fields of these dwarfs decay, they release electromagnetic radiation that propagates through space as radio signals.
The crimson dwarf is likely to emit a stellar wind of charged particles, akin to the one produced by our Sun. As the wind interacts with the white dwarf’s magnetosphere, it is rapidly accelerated, generating intense radio emissions.
As solar winds collide with Earth’s magnetic field, a breathtaking spectacle unfolds.
Researchers are familiar with certain methods akin to this one; essentially, fluctuations in the intensity of the red dwarf’s luminosity suggest that its white dwarf companion is bombarding it with intense radio radiation every 120 seconds.
While none of these techniques can match the vibrancy or sluggishness of long-period radio transients, future discoveries might uncover a unifying physical model capable of explaining all such phenomena.
There are also systems that potentially generate long-period radio pulsations.
As we’ve come to grasp the art of anticipating the unexpected, we’ll continue scouring the celestial expanse to uncover the secrets of this celestial enigma.
