An article published in the journal “Nature” reports a study on ASKAP J1832-0911, or simply ASKAP J1832, an object whose nature is still uncertain. A team of researchers combined data collected by different instruments, including NASA’s Chandra X-ray Observatory and the ASKAP radio telescope, to detect the emissions coming from this object. This allowed them to reveal anomalies with respect to the categories considered to try to identify it.
The radio emissions led to cataloging it as a long-period radio transient, but ASKAP J1832 has variable emissions of the same duration in X-rays as well. An object with that type of emissions has never been found before, so it arouses a lot of curiosity. It could be a magnetar or a white dwarf with a companion star, but its behavior remains strange, so the investigations will continue.
The so-called long-period radio transients are a category created in recent years of objects that emit radio emissions in long-duration cycles. An article published in “The Astrophysical Journal Letters” in November 2024 offered evidence that one of them, catalogued as GLEAM-X J0704−37, is a red dwarf with a companion that is probably a white dwarf whose interaction powers the radio emissions. However, the case of ASKAP J1832 shows some differences.
The radio emissions from that long-period radio transient were also detected by the Chinese DAocheng Radio Telescope (DART), and a team of researchers led by Professor Di Li reported their study in an article published on the scientific server arXiv in November 2024. In that study, the source is listed as DART J1832-0911 and associated with a supernova remnant. However, the association seems only apparent when looking at these objects from Earth, but actually, they could be very far from each other. The Chinese study cites the search for X-ray emissions in the archive of the ESA XMM-Newton space telescope, but without success. A neutron star is mentioned as the most likely source of those emissions.
Now, in this new international study, the object called ASKAP J1832 shows a radio emission with a periodicity of 44 minutes that makes it, at least apparently, a typical long-period radio transient. However, that periodicity was detected in X-rays as well, and it’s the first time that this occurred in an object of that type. For this reason, astronomers wonder whether this is another case of a white dwarf that has a star as a companion, or it’s another type of object. If it were a white dwarf, it would be the one with the strongest magnetic field known for this type of object in the Milky Way.
The possibility that ASKAP J1832 is a neutron star was examined by the researchers. Pulsars emit radio waves that vary in intensity in very short cycles, to the point that there are several cycles per second. A neutron star stripping material from a companion has different characteristics in its radio and X-ray emissions.
One possibility is that ASKAP J1832 is a magnetar, another class of neutron stars with a very strong magnetic field. Some of its X-ray characteristics point to a magnetar older than half a million years, but those objects typically don’t emit such bright and variable radio waves.
Despite both X-ray and radio observations, there’s still no definitive answer about the nature of ASKAP J1832. Perhaps, some key detection is still missing to solve the mystery. Perhaps some models of astronomical objects are still incomplete.
Observations conducted between February and August 2024 with the Chandra X-ray Observatory showed a drop in emission intensity from a very high level to the disappearance of X-rays, which coincided with a noticeable weakening of the radio emissions. This makes further study more difficult unless there’s a new increase in their intensity. The researchers also hope to find other long-period radio transients that also have cycles of X-ray emission to search for new clues about this cosmic mystery.
