In 2024, an international team of researchers discovered a radio-emitting cosmic source—probably a neutron star—that was spinning very slowly, making one revolution every 54 minutes. New data showed that the source's speed had slowed to even greater values, and it continued to emit radio waves, which, according to theory, should not be the case. The scientists' discovery challenges the idea of neutron stars.
In 2006, astrophysicists discovered a new type of cosmic object that emits pulses of radio radiation at a much lower frequency than expected. These sources were called ""transient radio bursts"They are characterized by extremely long rotation periods, from several minutes to an hour.
The radiation emitted by radio transients is very similar to that emitted by radio pulsars, a class of neutron stars. Therefore, some scientists consider radio transients to be neutron stars.
The new sources have left scientists in a dead end, because it was previously believed that the pulses of radio emission stop if the rotation of the radio source slows down - it starts taking more than a minute to complete one revolution. The speed of rotation or weak magnetic field of the neutron star no longer produces pulses. researchers have never observed this kind of event. The main question that worries scientists is: how do such objects continue to emit in the radio range, despite such a slow rotation? There is currently no answer.
Neutron stars generate streams of radio radiation that reach Earth in the form of periodically repeating bursts, called pulses. This is due to the rotation of the magnetic poles of neutron stars. To an observer, the radiation from the source appears to flicker, disappearing and reappearing, and this "pulsation" occurs with a steady periodicity.
In 2024, an international team of astrophysicists led by Manish Kaleb (Manisha Caleb) from the University of Sydney (Australia) discovered an unusual long-period radio source, ASKAP J1935+214, which rotated very slowly — making one revolution every 53,8 minutes.
According to the researchers, ASKAP J1935+214 is located about 13 light-years from Earth and is likely to have a diameter of 10 to 20 kilometers. During the radio transient, scientists recorded three different states: a strong polarized pulse lasting 10-50 seconds, a weaker (26 times) pulse lasting 370 milliseconds, and then an interval without pulses.
Now, Caleb and her colleagues have reported that ASKAP J1839-0756 has begun to rotate at a new record low rate – one rotation in 6,45 hours, which is unusual for radio transients. At the same time, it continues to emit radio waves. No known cosmic radio source has shown such behavior before. In addition, the authors of the scientific work told about another strangeness of the object.
Typically, a neutron star emits two relatively narrow beams from one of its magnetic poles. But ASKAP J1839-0756 is different. The source emits additional pulses from a second, opposite magnetic pole. This additional signal is weaker and is called an "interpulse" because it appears between the main pulses. ASKAP J1839-0756 is the first such object to have an interpulse.
Caleb's team initially suggested that the new source was a magnetized white dwarf — a failed neutron star that didn't have enough mass to become a neutron star. The researchers then suggested that ASKAP J1839-0756 was a magnetar, a rare class of neutron stars with magnetic fields trillions of times stronger than the most powerful MRI machines on Earth. Scientists had previously discovered slow magnetars, which rotate on their axis every 6,67 hours, but none of them emitted radio waves at the low frequencies that ASKAP J1839-0756 does.
"This object completely changes our understanding of the mechanisms of radio emission from neutron stars. If it is a magnetar, then it is certainly unique," Caleb explained.
The authors of the scientific work noted that in the near future, due to the atypical characteristics of ASKAP J1839-0756, scientists will have to review the knowledge accumulated over 60 years about the formation of neutron stars and rethink current ideas about the evolution of these bodies. The results of the study by the Caleb team were published in the journal Nature Astronomy .