Puzzling slow radio pulses are coming from space. A new study could finally explain them
Astronomers have been puzzled by repeating cosmic radio pulses, known as long-period transients, since their initial discovery in 2022. A new study, published today in Nature Astronomy, offers a potential explanation for these enigmatic signals.
Unraveling the Mystery of Slow Radio Pulses
Radio astronomers routinely observe pulsars – rapidly rotating neutron stars that emit beams of radio waves. These beams sweep across Earth, creating a pulsing effect akin to a cosmic lighthouse. However, long-period transients exhibit much slower periods, ranging from 18 minutes to over six hours. This presented a challenge to existing understanding, as neutron stars were not thought capable of producing radio waves at such slow rotation rates.
A White Dwarf Solution
Researchers have now presented evidence suggesting that at least one long-period transient, designated GPM J1839-10, is not a neutron star at all, but a white dwarf star. White dwarfs are the remnants of dead stars, comparable in size to Earth but containing the mass of our sun. This white dwarf appears to be generating powerful radio beams in conjunction with a companion star, an M-type dwarf, implying that similar systems may be responsible for other long-period transients.
The Heartbeat of GPM J1839-10
GPM J1839-10, discovered in 2023, stands out due to its unusually long lifespan and consistent signal. Observations spanning back to 1988 revealed pulses arriving in groups of four or five, with pairs of groups separated by two hours, repeating every nine hours. This stable pattern strongly suggests a binary system with a nine-hour orbital period, consistent with a white dwarf–M-dwarf pairing.
The signal’s unique “heartbeat” pattern, observed through a series of “round-the-world” observations using the Australian SKA Pathfinder (ASKAP), the MeerKAT radio telescope in South Africa, and the Karl G. Jansky Very Large Array in the United States, provides crucial clues to its nature. The data allowed researchers to refine the orbital period to within 0.2 seconds.
Modeling the Emission
Inspired by previous research on white dwarf pulsars, scientists modeled GPM J1839-10 as a white dwarf emitting a radio beam as its magnetic pole sweeps through the stellar wind of its companion. This model accurately predicts the observed heartbeat pattern and allows for reconstruction of the system’s geometry, including the distance and mass of the stars. Further analysis has even revealed variability in optical data, corroborating the radio signal findings.
Frequently Asked Questions
What are long-period transients?
Long-period transients are cosmic radio pulses that repeat every few minutes or hours, a much slower rate than typical pulsars.
What is a white dwarf?
A white dwarf is the remnant of a dead star, roughly the size of Earth but with the mass of the sun.
How was GPM J1839-10 studied?
GPM J1839-10 was studied using a series of “round-the-world” observations with three telescopes: ASKAP, MeerKAT, and the Karl G. Jansky Very Large Array.
As research continues, astronomers may uncover more examples of these white dwarf binary systems, potentially revealing a broader population of long-period transients and deepening our understanding of the universe’s diverse radio emissions.