Scientists Are Stumped by Mysterious Pulsing 'Star'

Something strange is going on 15,000 light years from Earth. Out at that distant remove, somewhere in the constellation Scutum, an unexplained body is semaphoring into space, blinking in both X-ray and radio frequencies once every 44 minutes in a way never seen by astronomers before. The object could be a white dwarf—an Earth-sized husk that remains after a star has exhausted its nuclear fuel. Or not. It could also be a magnetar—a neutron star with an exceedingly powerful magnetic field. Unless it’s not that either.

“Astronomers have looked at countless stars with all kinds of telescopes and we’ve never seen one that acts this way,” said astronomer Ziteng Wang of Curtin University in Australia, in a statement that accompanied the May 28 release of a paper in Nature describing the object, for which he was lead author. “It’s thrilling to see a new type of behavior for stars.”

So what exactly is the mysterious body—which goes by the technical handle ASKAP J1832—and how common is this species of object?

ASKAP J1832 is by no means unique in the universe in sending out energy in steady flashes. Pulsars—rapidly spinning neutron stars—do too. But pulsars flash much faster than ASKAP J1832 does, on the order of milliseconds to seconds. In 2022, astronomers discovered a type of object known as a long-period transient, which, like ASKAP J1832, sends out flashes of radio waves on the order of tens of minutes. So far 10 such bodies have been found, but none identical to ASKAP J1832, which is the first to emit X-rays too.

What’s more, ASKAP J1832’s emissions have changed over time. During one observation with NASA’s orbiting Chandra X-Ray Observatory in February 2024, the object was prodigiously producing both X-rays and radio waves. During a follow-up observation six months later, the radio waves were 1,000 times fainter and no X-rays were detected. That was a puzzle. 

“We looked at several different possibilities involving neutron stars and white dwarfs, either in isolation or with companion stars,” said co-author Nanda Rea of the Institute of Space Sciences in Barcelona, Spain, in a statement. “So far nothing exactly matches up, but some ideas work better than others.”

One of those ideas is the magnetar, but that doesn’t fit precisely, due to ASKAP J1832’s bright and variable radio emissions. The white dwarf remains a possibility, however in order to produce the amount of energy it does, ASKAP J1832 would have to be orbiting another body in a formation known as a binary system, and so far that second body hasn’t been detected. Viewed from Earth, ASKAP J1832 appears to be located in a supernova remnant, a cloud of hot gas and high energy particles that remains after an aging star meets its explosive end. But the authors of the paper concluded that the remnant merely lies in the foreground of the observational field with ASKAP J1832 in the background, the way an earthly cloud can drift in the path of the sun.

So for now, the object remains a riddle—one that will be investigated further. “Finding a mystery like this isn’t frustrating,” said co-author Tong Bao of the Italian National Institute for Astrophysics, in a statement. “It’s what makes science exciting.”