A pair of stars spiraling around each other explains the origin of a new source of repetitive radio bursts detected by astronomers, named ASKAP J1745.
In recent years, researchers have come across mysterious bursts of radio signals known as long-period transients, which repeat very slowly. They appeared unexpectedly during wide telescope scans of the sky.
So far, only about a dozen of these peculiar sources have been catalogued, and scientists are still trying to understand exactly their nature.
In a recent study published inNature Astronomy, the team reports an unprecedented detection: radio and X-ray explosions that repeat with each orbit.
ASKAP J1745 stands out because, unlike 10 of the 12 known long-period transients, it was possible to determine its origin. Additionally, astronomers have observed it with multiple telescopes that capture different types of light.
The famous Rosetta Stone, which carried the same message in three different scripts, made it possible to decipher the hieroglyphs of ancient Egypt. Likewise, the extra data obtained about ASKAP J1745 should help astronomers clarify the enigma of all long-period transient phenomena.
What do long period radio transients look like?
Long-period transients are space objects that emit bright, repeating bursts of light at radio wavelengths. Little is known about most of them. Many appear near the dusty region at the center of the Milky Way, which complicates observations in visible light.
Even with only a dozen examples identified, they exhibit different characteristics. Their radio pulses return at intervals ranging from minutes to hours.
Some sources have maintained regular pulses for more than 30 years, while others stop for days or are inactive for long periods.
Where do they come from?
At first, astronomers suspected that the long-period transients were very slowly rotating neutron stars known as pulsars. These objects are the dense supernova remnant cores of massive stars.
The first radio signals discovered were repeated every approximately 20 minutes, a much slower rate than that of a common pulsar, which emits every few seconds.
Furthermore, as pulsars lose rotation speed, they tend to stop emitting radio, which would make detecting bursts at such slow rotations unlikely.
So scientists explored other hypotheses, including white dwarfs — the cooled remnants of less massive stars. Recently, evidence of long-period transients has emerged in binary systems with a white dwarf and a lower-mass red dwarf.
The discovery of ASKAP J1745
ASKAP J1745 is a new long-period radio transient identified with the ASKAP radio telescope, operated by CSIRO, Australia’s national science agency. This is the first source of its type classified as a cataclysmic variable.
Cataclysmic variables are systems formed by two stars, one of them a white dwarf, that orbit close enough to interact. The white dwarf’s gravity pulls material from its companion, a process known as accretion, which also characterizes accreting white dwarf binaries.
Recently, another form of long-period radio signal associated with X-ray bursts has been recorded, which repeats with the same periodicity as radio waves. Still, the exact cause of these explosions and their timing remained unclear.
For the first time, combined observations from radio, X-ray and optical telescopes have shown that ASKAP J1745 generates X-ray and radio bursts with each orbit of the two stars.
In these fast-orbiting systems, X-rays arise from the heating of material flowing toward the white dwarf.
Bright radio bursts posed a greater enigma, but confirmation of an accreting binary system helped solve the mystery.
The type of pulsed radio emission detected is usually caused by energetic particles interacting with intense magnetic fields. In this case, there is the ideal combination: two stars with very strong magnetic fields, thousands of times greater than those of an MRI machine, and charged particles flowing from the companion star to the white dwarf.
What does this mean for the future of astronomy?
This discovery sets itself apart because it offers more information and over a wider range of wavelengths than any previous long-period transient.
Just as the Rosetta Stone was essential for deciphering ancient Egyptian symbols, ASKAP J1745 should serve as a reference for understanding the origins of other long-period radio transients that lack data in other bands of the spectrum.
ASKAP J1745 is the first long-period transient system to show signs of accretion across the entire spectrum, from radio waves to visible light and X-rays. This flow of charged material represents a key ingredient for generating the observed radio bursts.
Studying the mechanism behind these long-duration bursts opens up a new laboratory for investigating extreme physics, such as plasma flows and magnetic fields, under conditions impossible to reproduce on Earth.