According to Nature, scientists have discovered a star that behaves unlike any other, providing new insights into the origins of a new class of intriguing objects.
X-ray: NASA/CXC/ICRAR, Curtin Univ./Z. Wang et al.; Infrared: NASA/JPL/CalTech/IPAC; Radio: SARAO/MeerKAT; Image processing: NASA/CXC/SAO/N. Wolk. Image Credit: NASA
Astronomers used data from NASA's Chandra X-ray Observatory and the SKA Pathfinder (ASKAP) radio telescope in Wajarri Country, Australia, to examine the behavior of the discovered object, ASKAP J1832−0911.
ASKAP J1832 belongs to a group of objects known as “long-period radio transients,” first identified in 2022. These objects exhibit predictable variations in radio wave strength over spans of several tens of minutes. This is thousands of times longer than the periodic changes observed in pulsars, which are rapidly spinning neutron stars with several variations every second. ASKAP J1832’s radio wave intensity cycles every 44 minutes, classifying it as a long-period transient.
Using Chandra, the scientists observed that ASKAP J1832's X-rays fluctuate every 44 minutes. This is the first time an X-ray signal has been detected in a long-period radio transient.
The composite image combines Chandra X-rays (blue) with Spitzer Space Telescope infrared data (cyan, light blue, teal, and orange), as well as LOFAR radio data (red). An inset depicts a more comprehensive image of the area surrounding this odd object in X-ray and radio light.
Using Chandra and the SKA Pathfinder, astronomers discovered that ASKAP J1832 saw a significant reduction in X-rays and radio waves over the period of six months. This combination of 44-minute cycles in X-rays and radio waves, as well as months-long variations, is unprecedented in the Milky Way galaxy.
According to the study team, ASKAP J1832 is unlikely to be a pulsar or neutron star extracting material from a companion star since its features do not correspond to the normal strengths of radio and X-ray emissions for such objects.
Some of ASKAP J1832’s features could be consistent with a neutron star that has an exceptionally strong magnetic field (a magnetar) estimated to be over half a million years old. However, other aspects, like its intense and variable radio emissions, are hard to reconcile with a magnetar of that age.
In the sky, ASKAP J1832 appears to lie within a supernova remnant, the remains of an exploded star, which often contains a neutron star formed during the blast. However, the researchers found that the proximity is most likely a coincidence and that the two are unrelated, leading them to examine the possibility that ASKAP J1832 may not contain a neutron star.
They concluded that an isolated white dwarf doesn't account for the data, but a white dwarf with a companion star might. However, this scenario would require the white dwarf to have the most powerful magnetic field ever observed in our galaxy.
Another team, led by Di Li from Tsinghua University in China, found this source independently using the DAocheng Radio Telescope and submitted their research to arXiv on the same day as Dr Wang's team. They did not report the X-ray behavior indicated above.
NASA's Marshall Space Flight Center in Huntsville, Alabama, oversees the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center oversees research operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.