Something in deep space is pulsing and sending signals to Earth in steady, like clockwork, 16-day cycles.

Scientists have discovered the first fast radio burst, a mysteriously repeating signal beating at a steady rhythm, coming from the outskirts of another galaxy, about 500 million light years from Earth.

This marks the first time that scientists have ever detected periodicity in these signals, which are known as fast radio bursts (FRBs), and is a major step toward unmasking their sources.

FRBs are one of the most tantalizing puzzles that the universe has thrown at scientists in recent years. First spotted in 2007, these powerful radio bursts are produced by energetic sources, though nobody is sure what those might be. FRBs are also mystifying because they can be either one-offs or “repeaters,” meaning some bursts appear only once in a certain part of the sky, while others emit multiple flashes to Earth.

A Canadian study further hypothesized, after spending more than a year observing and collecting data on the phenomenon, the cadence and clustering of the visible bursts, and some cycles did not produce any visible bursts, but those that did were all synced up to the same 16-day intervals.

There is not a lot of consensus at this time in the scientific community.

One study published said it’s possible that we are witnessing a binary system containing a massive star and a super-dense stellar core known as a neutron star. The neutron star would emit radio bursts, but those signals would be periodically eclipsed by opaque outflowing winds from its giant companion.

Another published report deduced the FRB rhythm isn’t tempered by another object, and is sending out the pulses directly from the source. Scientists say that flares from highly magnetized neutron stars, called magnetars, might be the source of some FRBs. But since magnetars tend to rotate every few seconds, a 16-day cycle does not match the expected profile of a magnetar-based FRB.

The Truth is Out There.