Mysterious radio waves are radiating from an unknown object at the heart of the Milky Way, astronomers say

• Astronomers detected mysterious radio waves from the center of the galaxy that vary dramatically and seem to shut off at random.
• The waves' origin is unknown, so they hint at the existence of a new type of celestial object.
• The signal doesn't look like the kind that comes from stars, planets, or even dead stars.

Mysterious radio waves are emanating from the heart of our galaxy, and astronomers don't know what's making them.

All celestial objects emit radio waves – planets, stars, dead stars, and even asteroids. But researchers at the University of Sydney recently detected radio signals that do not match any known types. The waves, originating near the center of the Milky Way, don't seem to be coming from any kind of star, planet, or space rock that scientists have seen before.

Even stranger, the strength of this signal has waxed and waned dramatically over just a few months. Most objects in the galaxy, by contrast, don't change much year to year – and therefore nor do their radio waves.

"The signal switches on and off apparently at random. We've never seen anything like it," Ziteng Wang, the lead author of the new study and a PhD student in physics at the University of Sydney, said in a press release.

A paper describing the discovery was published Tuesday in The Astrophysical Journals. In it, Wang and his coauthors concluded that the mysterious source of this radio signal "may represent part of a new class of objects."

The radio signal disappeared for months, reemerged suddenly, then vanished again

Whatever the mysterious object is that's responsible for this phenomenon, it was emitting strong radio waves through most of 2020. The researchers detected six signals over nine months, using the ASKAP radio telescope in western Australia.

After that, the team tried to find the object in visible light, but they came up empty-handed. They couldn't find it in X-ray or infrared light, either.

So they switched back to radio waves, at first using Australia's Parkes radio telescope, but they lost the source of the signal and couldn't detect anything for a while. Then they turned to a different radio telescope - the MeerKAT observatory in South Africa - and observed the area for 15 minutes every few weeks.

Finally, they caught the radio signal once more, but it disappeared in a single day. That was strange, since the six signals they'd caught with ASKAP had each lasted for weeks.

"This object was unique in that it started out invisible, became bright, faded away, and then reappeared. This behavior was extraordinary," Tara Murphy, a professor at the University of Sydney who is Wang's PhD supervisor, said in the release.

Murphy and Wang are not talking about visual brightness - a "bright" radio signal is just a strong one.

"The brightness of the object also varies dramatically, by a factor of 100," Wang said in the release.

In an email, Murphy told Insider "that is part of what makes it unusual."

"Objects that are hot (e.g. stars) typically emit visible light, which is why we ruled out a normal star as one of the possible interpretations for this object," she wrote. "It could be a very very cool star that is too weak to detect the visible light from but has bright radio flares."

The mysterious radio signal shares some traits with signals from a class of objects called "galactic center radio transients" that were discovered in the 2000s. But researchers don't know much about those objects either, except that they emit low-frequency, highly polarized radio waves with no detectable X-rays. Still, the new signal has properties that don't match those from the radio transients.

"We don't really understand those sources, anyway, so this adds to the mystery," Wang's co-supervisor, David Kaplan from the University of Wisconsin-Milwaukee, said in the release.