Astronomers have been puzzled by powerful radio-wave bursts that appear for only a few milliseconds, but emit as much energy as the sun does over the course of 300,000 years.

What could create that much energy? According to a new study published in Science, one likely candidate is a neutron star collapsing into a black hole, an event recently dubbed a blitzar.

"When the black hole forms, the magnetic field will be cut off from the star and snap like rubber bands," explains astronomer Heino Falcke in New Scientist.

Another leading theory is that the radio-wave bursts come from magnetars, which are highly magnetic neutron stars.

The waves could also be caused by two colliding neutron stars, evaporating black holes, or an entirely new type of astrophysical event, according to James Cordes, an astronomer at Cornell University.

The intense bursts were first discovered six years ago. Recently, astronomers found four of them while sweeping the sky with the Parkes radio telescope in New South Wales, Australia.

The resulting study now concludes that they are probably common occurrences, appearing as often as every 10 seconds. Despite the fact that these bursts appear all the time, only six of them have been observed.

That is because telescopes can only observe small patches of sky, meaning “you have to look for a long time before seeing many,” Dan Thornton, an astronomer at the University of Manchester, tells Discovery. “This is why we have only detected a handful so far.”

Unlike most radio waves we detect, these came from beyond our Milky Way galaxy, originating between six billion and nine billion years ago. That would make them around half as old as the universe itself.

Scientists are hoping that the radio-wave bursts can help shed light on what kind of gas fills the gaps between galaxies.