ASKAP J1832, located near the center of the Milky Way, pulses every 44 minutes with radio waves and X-rays – an unprecedented rhythm that suggests a new type of astronomical object.
Researchers have discovered a star that breaks all the rules, and it may belong to a whole new class of mysterious cosmic objects. Using a combination of observations from NASA's Chandra X-ray Observatory and the ASKAP radio telescope in Australia, astronomers focused on the object called ASKAP J1832−0911 (or ASKAP J1832 for short), and discovered findings that have never been seen before. These objects, which were first discovered in 2022, emit repeated bursts of radio waves, but at a much slower rate than the rapid pulses of traditional pulsars. While regular pulsars flash several times a second, ASKAP J1832 pulses every 44 minutes—a rate that puts it in a category of its own.
Radio and X-ray at the same time
What makes ASKAP J1832 even more extraordinary is that it doesn't just pulsate in radio waves. NASA's Chandra X-ray Observatory revealed that it also emits X-rays in the same 44-minute cycle. This is the first time that X-ray signals have been detected from this type of object. In a stunning composite image, the team combined X-ray data from Chandra (in blue), infrared data from NASA's Spitzer Space Observatory, and radio data from LOFAR to create a vivid portrait of this stellar enigma.
A confusing phenomenon: emissions decay
Even more puzzling is the fact that ASKAP J1832's emissions have been fading dramatically over the past six months, both in radio and X-rays. This combination of short-term pulses and long-term changes is unprecedented in our Milky Way galaxy, leaving scientists with more questions than answers.
The research team says it is unlikely that ASKAP J1832 is a pulsar or a neutron star that is pulling in material from a companion star, as its properties do not match the usual radio and X-ray signal strengths of such objects. Some of ASKAP J1832's properties could be explained by a neutron star with an extremely strong magnetic field, called a magnetar, that is more than half a million years old. However, other properties – such as its bright and variable radio emission – are difficult to explain for such an old magnetar.
Clues from a nearby supernova remnant
In the sky, ASKAP J1832 appears to be inside a supernova remnant—the remains of an exploded star, sometimes containing a neutron star formed from the supernova. However, the research team determined that this proximity was likely coincidental, and the two objects are not related, prompting them to consider the possibility that ASKAP J1832 does not contain a neutron star at all. They concluded that an isolated white dwarf does not explain the data, but a white dwarf with a companion star could—but that would require the strongest magnetic field known for a white dwarf in our galaxy.
Publication of the study
A paper by Ziteng Wang of Curtin University in Australia and colleagues describing these results was published in the journal Nature. Another team independently discovered this source using the DAocheng radio telescope, and submitted their paper to arXiv on the same day as the team led by Dr. Wang submitted their paper. However, the second team did not report the X-ray behavior described here.
