Astronomers have discovered a bizarre, repeating radio signal at the Milky Way’s core that is unlike any other energy signature ever studied.

The energy source is exceedingly fussy, according to a recent research approved for publication in The Astrophysical Journal and released on the preprint service arXiv, appearing bright in the radio spectrum for weeks at a time and then totally disappearing within a day. This behavior doesn’t quite fit the profile of any known type of celestial body, the researchers wrote in their study, and thus may represent “a new class of objects being discovered through radio imaging.”

The radio source, known as ASKAP J173608.2321635, was found using the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope, which is located in Australia’s distant outback. The strange signal happened 13 times in an ASKAP poll between April 2019 and August 2020, never lasting more than a few weeks, according to the researchers. This radio source is very variable, coming and vanishing at whim, and does not show in any other radio telescope data prior to the ASKAP survey.

When the researchers attempted to match the energy source with observations from other telescopes, such as the Chandra X-ray Observatory and the Neil Gehrels Swift Observatory, as well as the Visible and Infrared Survey Telescope for Astronomy in Chile, which can detect near-infrared wavelengths, the signal vanished. ASKAP J173608.2321635 is a radio ghost that seems to defy explanation, with no apparent emissions in any other section of the electromagnetic spectrum.

Prior studies have discovered low-mass stars that flare up with radio energy on a regular basis, but such flaring stars typically have X-ray counterparts, the researchers said. As a result, a stellar source is unlikely in this case.

The team also believes that dead stars, such as pulsars and magnetars (two types of ultradense, collapsed stars), are unlikely answers. While pulsars may send powerful beams of radio light past Earth, they rotate with regular periodicity, moving their lights past our telescopes in hours instead of weeks. Magnetars, on the other hand, always contain a powerful X-ray counterpart with each of their outbursts, unlike ASKAP J173608.2321635.

The closest match is a mystery kind of object known as a galactic center radio transient (GCRT), which is a rapidly blazing radio source that brightens and decays at the Milky Way’s center over a few hours. So far, just three GCRTs have been confirmed, and they all arrive and disappear far faster than this new ASKAP object. The few known GCRTs, on the other side, glow with the same brightness as the mysterious signal, and their radio flare-ups are never accompanied by X-rays.

If this new radio item is a GCRT, its properties exceed what astronomers thought GCRTs could do, the researchers concluded. Radio surveys of the galactic center in the future should assist to solve the mystery.