An illustration showing a large orange sphere on the left and a much smaller bright object on the right, surrounded by dense looping white lines. A glowing, curved blue-green line goes from the large sphere to the smaller object. The background is dark teal with scattered tiny white specks.

Rose et al. have uncovered the strongest evidence yet for the origin of long period radio transients. Using ASKAP, the team discovered a white dwarf shredding material from its larger, but less dense, companion star. As this material spirals in, it produces powerful bursts of radio waves and X-rays in a cycle that repeats every 1.4 hours. The newly identified system, ASKAP J1745−5051, consists of a white dwarf (a dense stellar remnant roughly the size of Earth but with the mass close to that of the Sun) paired with a larger but lower-mass red dwarf star of about one-tenth the Sun’s mass. The two stars orbit each other extremely closely, with a period of 1.3 hr. As material from the less massive star is drawn towards the white dwarf, it heats up and emits X-rays. At the same time, interactions between the stars’ magnetic fields generate regular radio bursts. The team found that the radio emission likely originates where the magnetic fields of the two stars meet and interact with the charged material being ripped from the companion star, producing tightly beamed bursts of radiation. For this multi-wavelength study, the team used the ASKAP and ATCA radio telescopes in Australia, the MeerKAT radio telescope in South Africa, the SOAR and Magellan optical telescopes in Chile, and the space-based Swift (UV/X-ray) and Einstein Probe (X-ray) telescopes.

Long-period radio transients were initially thought to be slow-spinning pulsars. However, current models suggest neutron stars rotating this slowly should not be able to produce such signals.  The new discovery strengthens an alternative explanation: that at least some of these mysterious bursts come from systems of two stars, involving white dwarfs. The image above shows an illustration of an accreting white dwarf (Image credit:  Carl Knox (OzGrav, Swinburne University of Technology) and Joshua Preston Pritchard (CSIRO))