Astrophysicists are stumped by an odd energy signal recently detected in the heart of the Milky Way galaxy, CNN reports.

The radio signal, picked up by a telescope in Australia, is unlike any phenomenon scientists have seen before and could suggest a previously unknown stellar object, according to a new study.

When it was initially discovered, researchers said it appeared 13 times between April of 2019 and August of 2020, never lasting in the sky for more than a few weeks. 

The object's brightness appeared to experience extreme shifts and its signal seemed to go on and off at random.

Ziteng Wang, lead author of a new study in The Astrophysical Journal and a doctoral student in the School of Physics at The University of Sydney said, "The strangest property of this new signal is that it has a very high polarisation. This means its light oscillates in only one direction, but that direction rotates with time."

At first, scientists assumed the signal was coming from a pulsar, which is a very dense rapidly spinning neutron (dead) star, or a type of star that emits solar flares.

But upon further investigation the odd signals don't match what astronomers expect from any known celestial body.

"This object was unique in that it started out invisible, became bright, faded away and then reappeared. This behaviour was extraordinary," said study coauthor Tara Murphy, a professor at the Sydney Institute for Astronomy and the School of Physics at The University of Sydney, in the release.

After the initial discovery in Australia, follow-up observations were attempted with the the Parkes radio telescope in New South Wales and South African Radio Astronomy Observatory's MeerKAT telescope.

While the Parkes telescope did not pick up the source, the South African-based research produced results.

"We then tried the more sensitive MeerKAT radio telescope in South Africa. Because the signal was intermittent, we observed it for 15 minutes every few weeks, hoping that we would see it again," Murphy said in the statement.

"Luckily, the signal returned, but we found that the behaviour of the source was dramatically different -- the source disappeared in a single day, even though it had lasted for weeks in our previous ASKAP observations."

According to Live Science, some experts wonder if the source of the radio waves could be a mysterious class of object known as a galactic center radio transient (GCRT), a rapidly glowing radio source that brightens and decays near the Milky Way's center, usually over the course of a few hours.

At this time, only three GCRTs have been confirmed, and all of them appear and disappear much more quickly than this new ASKAP object does. But the few known GCRTs do shine with a similar brightness as the mysterious signal, and their radio flare-ups are never accompanied by X-rays.

In any case, some scientists hope that the much-anticipated construction of powerful telescopes will shed new light on the phenomenon.

One such telescope is the Square Kilometre Array, which is described as an international effort to build the world's largest radio telescope.

It's expected to be completed within the next decade.

In the meantime, scientists are doing what they can to understand more about the mysterious object, which has been named after its coordinates: ASKAP J173608.2-321635.