A small, dense dead star captured tearing apart material from a companion star has helped astronomers solve one of the universe’s most baffling mysteries — and researchers from the UNC College of Arts and Sciences played a key role in uncovering the answer.
Working as part of an international collaboration, Carolina astronomers Igor Andreoni, Brad Barlow, and Jonathan Carney have helped pinpoint the source of a long-mysterious class of cosmic signals known as radio transients. results, Published in Nature AstronomyThey provide some of the strongest evidence yet for the origin of these unusual bursts of radio waves, which can repeat over periods of minutes to hours and have mystified astronomers since their discovery.
The breakthrough began when researchers led by graduate student Kofi Rose at the University of Sydney used the Australian Square Kilometer Pathfinder (ASKAP) radio telescope to detect powerful bursts of radio waves that repeated every 1.4 hours. Observations using multiple telescopes indicated that the signals were coming from a binary star system containing a white dwarf, a dense stellar remnant roughly the size of Earth but with a mass similar to the Sun, and a low-mass companion red dwarf.
To test the idea, the Carolina team quickly secured observing time on the 4.1-meter Southern Astrophysical Research (SOAR) telescope in Chile.
“SOAR observations were essential to the success of this project,” said Andreoni, an assistant professor in the Department of Physics and Astronomy at UNC-Chapel Hill. “Our data revealed that we were looking at two stars orbiting each other, and we could measure the rotation period.”
Late-night observations by Andreoni, Barlow and Carney revealed clear signs in the system’s light confirming the presence of a cataclysmic magnetic variable — a binary system in which a white dwarf pulls material from a companion star. As that material heads toward the white dwarf, it heats to extreme temperatures, producing distinctive optical and x-ray emissions.
“The atmosphere in the observation room that night was electric,” said Barlow, an associate professor in the department of physics and astronomy at the University of North Carolina at Chapel Hill. “As soon as the spectrum appeared on the screen, the clear emission lines told us that we had something special on our hands. It’s not often that they play a role in discoveries of this magnitude.”
The system, called ASKAP J1745−5051, consists of a white dwarf and a red dwarf star with a mass of about one-tenth the mass of the Sun. The stars orbit each other so closely that they complete their full orbit in just over an hour. As material is stripped from the red dwarf and collected in the white dwarf, interactions between the stars’ powerful magnetic fields generate regular radio bursts that can be detected over vast distances in space.
“The accuracy and sensitivity of the SOAR telescopes’ instruments were key,” said Carney, a graduate student in the Department of Physics and Astronomy at UNC-Chapel Hill. “The observations were made possible in part thanks to the Goodman Spectrograph, an instrument designed by Carolina and installed on the SOAR telescope in Chile. UNC originally began the SOAR telescope project in 1987 to expand access to the southern sky for students and researchers.”
This discovery may finally explain the origin of some long-term radio transients. When astronomers first detected these signals, many suspected they came from unusually slow-spinning neutron stars known as pulsars. Current theories suggest that slowly rotating neutron stars should not be able to produce such emissions. The new results reinforce an alternative explanation: that some of these mysterious signals are generated by the interaction of binary star systems that include white dwarfs.
Researchers say ASKAP J1745−5051 could serve as crucial evidence to explain future discoveries. Just as the Rosetta Stone helped scientists decipher ancient Egyptian hieroglyphs, this system may provide astronomers with a reference point to determine whether the newly discovered long-range transient radio waves originate from pulsars, white dwarf binaries or other exotic objects.
In addition to solving a long-standing astronomical mystery, the system offers scientists a rare opportunity to study intense magnetic fields, high-energy plasmas, and the behavior of matter under conditions that cannot be reproduced in laboratories.
Written by Gabriella Nieman, University Communications and Marketing
