"Unlike Anything We Have Seen Before": Repeating Signal From Deep In Galactic Plane Puzzles Astronomers

Astronomers are puzzled after detecting an unusual, repeating long-period transient (LPT) signal emitted deep in the Galactic Plane.

Last year, a team from Australia’s national science agency, CSIRO, found the strange signal using the ASKAP radio telescope on Wajarri Country in Australia. The object, known as ASKAP J1832-0911, appears to emit a pulse of radio waves every 44 minutes.

"Long-period transients are a recently identified class of cosmic objects that emit bright flashes of radio waves every few minutes to several hours. This is much longer than the rapid pulses we typically detect from dead stars such as pulsars," lead author Ziteng (Andy) Wang explained in a piece for The Conversation, adding that what these LPTs are remains a mystery.

"Our discovery opens up a new window into the study of these puzzling sources. But it also deepens the mystery: the object we found doesn’t resemble any known type of star or system in our galaxy – or beyond."

What makes ASKAP J1832-0911 so unusual? The team correlated the signal with high-energy X-ray pulses detected by NASA’s Chandra X-ray Observatory, which had been coincidentally observing the same area of sky. Adding to the mystery of what causes these signals and why they turn "on and off" on these long and regular intervals comes the realization that they may emit higher-energy X-rays as well.

Searching through previous observations of the region, the team found no trace of the object prior to their own.

"This suggests something dramatic happened shortly before we first detected it – something powerful enough to suddenly switch the object 'on'," Wang continues. "Then, in February 2024, ASKAPJ1832 became extremely active. After a quieter period in January, the source brightened dramatically. Fewer than 30 objects in the sky have ever reached such brightness in radio waves."

The extremely bright source, roughly 15,000 light-years from Earth and lying in our own galaxy's plane, doesn't fit neatly with current models.

"This object is unlike anything we have seen before," Dr Wang added in a statement. "ASKAP J1831-0911 could be a magnetar (the core of a dead star with powerful magnetic fields), or it could be a pair of stars in a binary system where one of the two is a highly magnetised white dwarf (a low-mass star at the end of its evolution)."

"However, even those theories do not fully explain what we are observing. This discovery could indicate a new type of physics or new models of stellar evolution."

While this is a one off object, caught through chance in X-ray by a second telescope, it could be that other LPTs emit X-rays too.

“Finding one such object hints at the existence of many more," said second author Professor Nanda Rea from the Institute of Space Science (ICE-CSIC) and Catalan institute for Space studies (IEEC) in Spain. "The discovery of its transient X-ray emission opens fresh insights into their mysterious nature."

The discovery of ASKAP J1832-0911 could help narrow down what causes these repeating long-period transients, but for now, more observations of LPTs in X-ray are needed to gather more data and clues.

“We will continue to hunt for clues about what is happening with this object, and we’ll look for similar objects,” co-author Dr Tong Bao of the Italian National Institute for Astrophysics (INAF) – Osservatorio Astronomico di Brera in Italy, added in a Chandra statement. “Finding a mystery like this isn’t frustrating — it’s what makes science exciting!”

The study is published in Nature.