Astronomers Trace a Mysterious Long-Period Radio Transient to an Accreting White Dwarf Binary, ASKAP J1745-5051
Researchers pinpointed a repeating radio signal to a white dwarf pulling matter from a red dwarf companion every 1.4 hours, a 'Rosetta stone' for the class.
Overview
Astronomers have traced one of the sky’s puzzling repeating radio signals to a pair of stars orbiting one another, identifying the source as an accreting white dwarf binary designated ASKAP J1745-5051. According to ScienceDaily, the emissions repeat on a regular cycle every 1.4 hours, and the system consists of a white dwarf and a red dwarf locked in an extremely close orbit. The work was published in the journal Nature Astronomy, ScienceDaily reports.
What We Know
The object belongs to a class known as long-period radio transients, which produce bright, repeating bursts of radio waves on timescales of minutes to hours. As described by Phys.org, in a piece bylined by lead researcher Kovi Rose, the signal originates from “a pair of stars spiraling around each other.” Such sources remain rare: as Rose wrote for The Conversation, “To date, astronomers have only found a dozen of these weird sources, and we’re still trying to understand exactly what they are.”
The binary pairs a white dwarf, a dense stellar remnant roughly the size of Earth but with a mass comparable to the Sun, with a low-mass red dwarf companion that holds about one-tenth the Sun’s mass, according to ScienceDaily. The two stars complete an orbit in just over an hour, ScienceDaily reports. Material stripped from the red dwarf spirals onto the white dwarf, and this accretion drives the bursts. As Phys.org puts it, “This stream of charged material is a crucial ingredient for making the radio light we detect from these systems.”
The discovery rested on observations across multiple wavelengths. The repeating bursts were caught with CSIRO’s ASKAP radio telescope, the Australian Square Kilometre Array Pathfinder, according to EurekAlert!. To pin down the system, researchers turned to the 4.1-meter Southern Astrophysical Research (SOAR) Telescope in Chile for spectroscopy, EurekAlert! reports.
Lead researcher Kovi Rose, a PhD student at the University of Sydney’s School of Physics and CSIRO, framed the result as a first. “For the first time, we have pinpointed the origin of these signals, confirming the source to be a ‘cataclysmic variable’, or an accreting white dwarf star,” Rose said, according to Universe Today.
UNC-Chapel Hill astronomers contributed the optical follow-up that clinched the classification. “The SOAR observations were essential to the success of this project. Our data revealed that we were looking at two stars orbiting each other and we could measure the rotation period,” said Igor Andreoni, an assistant professor in the department of physics and astronomy at UNC-Chapel Hill, according to EurekAlert!. Brad Barlow, an associate professor in the same department, described the moment of detection: “The atmosphere in the observing room that night was electric. As soon as the spectrum came up on the screen, those unmistakable emission lines told us we had something special on our hands,” he said, per EurekAlert!.
What We Don’t Know
The finding does not by itself resolve every member of the class. As Rose noted, ASKAP J1745-5051 offers a template rather than a universal answer: “This system gives us a way to decode these signals. It could help us determine whether other long-period transients are more like pulsars or like white dwarf systems, acting like a stellar Rosetta stone,” Rose said, according to Universe Today. Some other long-period transients may still trace to neutron stars rather than white dwarfs.
Analysis
The broader value of ASKAP J1745-5051 is that it has been detected across radio, optical, and X-ray light, unlike many long-period transients seen only in the radio. Writing in The Conversation, Rose noted that “ASKAP J1745 is the first long-period transient showing signs of accretion across the spectrum of light – from radio waves to visible to X-rays.” That multi-wavelength visibility is what allowed the team to identify the underlying engine, and, as Phys.org notes, the system “will be key to deciphering the origins of other long-period radio transients that lack information at other wavelengths.”