A mysterious signal from space points to the ‘laziest’ neutron star scientists have ever seen

None of the more than 3,000 radio-emitting neutron stars discovered so far rotate as slowly as this new object. It is a mystery to researchers.

Astronomers have discovered a very strange object in the night sky. This is a neutron star that probably rotates more slowly than any other star ever measured. According to researchers, the object challenges our understanding of neutron stars. “The fact that the signal repeats itself at such a slow rate is extraordinary,” said study leader Manisha Caleb.

Neutron stars
To understand why this “lazy” neutron star is so unique, we first have to go back to what exactly neutron stars are. When large stars — about ten times the mass of our Sun — reach the end of their lives, they use up all their fuel and explode in a spectacular supernova. What’s left is an extremely compact stellar remnant, 1.4 times the mass of the Sun, confined to a sphere just 20 kilometers in diameter. The material is so compressed that the negatively charged electrons are compressed with the positively charged protons. This results in an object consisting of countless neutrally charged particles. This creates a neutron star.

fast
Because of the extreme physics involved in the collapse of these stars, neutron stars usually rotate at amazing speeds. It takes only a few seconds or even milliseconds to complete a circle around its axis. This is what makes the new discovery so remarkable. Because the signal from the newly discovered neutron star indicates that this star is rotating at a fairly slow pace. Concretely, it appears to complete a circle around its axis in just under an hour.

ASCAP J1935+2148
The “lazy” neutron star, named ASKAP J1935+2148, has set a new record. Because more than 3,000 radio-emitting neutron stars have been discovered so far, none of them rotate as slowly as this one. “It is unusual to find a candidate neutron star that emits radio pulses in this way,” Caleb says. The results were published today in Nature astronomy.

ASKAP radio telescope
Researchers tracked down the strange object thanks to the ASKAP radio telescope located in Western Australia. This telescope is capable of observing a large portion of the sky at once, which means it is able to capture phenomena that researchers are not even looking for. According to researcher Emil Lenk, ASKAP J1935+2148 would not have been found otherwise. “While we were observing gamma rays and looking for a fast radio burst, I suddenly noticed this object,” he explains. “ASKAP is one of the world’s leading telescopes for this type of research, because it continuously scans large parts of the sky. This allows us to detect even the smallest aberrations.”

Three different emission states
What is also noteworthy is that ASKAP J1935+2148 shows three different emission states. The first is a strong pulse that lasts for tens of seconds, the second is a weaker pulse that lasts for hundreds of milliseconds, and the third is a complete resting position without any pulses. “The MeerKAT radio telescope in South Africa played a crucial role in identifying these different cases,” Caleb says. “If the signals had not come from the same location in the sky, we would not have thought they came from the same object.”

A neutron star or white dwarf
The origin of the mysterious signal remains shrouded in mystery at this time. Although researchers have a doubt. For example, they argue that a slowly rotating neutron star is probably the most likely explanation. But the white dwarf is also on the list of suspects. An isolated white dwarf with an exceptionally strong magnetic field could also produce the observed signal. The strange thing is that a nearby, highly magnetically isolated white dwarf has never been discovered. On the other hand, a neutron star with intense magnetic fields could explain the observed emissions quite easily. Or, the object could also be part of a binary system, consisting of a neutron star or another white dwarf.

Reviewer
In short, more research is needed to confirm whether the object is a neutron star or a white dwarf. Regardless of the outcome, studying ASKAP J1935+2148 will provide us with valuable insights into the physics of these unusual objects. Because there is no doubt that the object challenges our understanding of the emission and evolution of neutron stars. “This discovery may force us to rethink our long-standing understanding of neutron stars or white dwarfs,” Caleb says. “Especially in terms of how radio waves are transmitted and what their inhabitants look like in our Milky Way Galaxy.”

This discovery once again highlights how much we can learn thanks to telescopes like ASKAP and MeerKAT. “Before the advent of these new telescopes, the dynamic radio sky remained largely unexplored,” says researcher Tara Murphy. “Now we can conduct in-depth research and often encounter many unusual phenomena. These events provide us with valuable insights into how physics works in extreme environments.