Fast radio bursts were once thought to be alien broadcasts. New research suggests the mysterious signals come from dead stars.

• Astronomers have linked a mysterious fast radio burst to its source for the first time: a dead star within our galaxy.
• The dead star, known as a magnetar, released an explosion of X-rays and gamma rays with a single radio burst.
• The discovery suggests that these mysterious radio signals all come from magnetars.

Somewhere beyond our galaxy, mysterious entities have been sending out bright bursts of radio waves. They last only a millisecond, careening through the cosmos.

Scientists first discovered one of these fast radio bursts in 2007, hidden in telescope data from 2001. Researchers soon determined that a new fast radio burst was probably booming across the cosmos every second. Some of them seemed to be repeating, with new explosions of radio waves coming from the same location at regular intervals.

For years, nobody knew what was producing these signals. Some speculated that alien societies could be beaming them to our galaxy. Others thought they could be ejecta from the final explosions of dying stars.

But new research shows that many of these pulses, if not all of them, are probably coming from magnetars, a type of neutron star. All neutron stars are the super-dense remains of a star's dying explosion, but magnetars are distinguished by their extremely powerful magnetic fields, which cause explosions of energy that can produce radio bursts. That's the conclusion of three studies published Wednesday in the journal Nature.

Until this year, every known fast radio burst (FRB) had resonated from beyond the Milky Way, making them nearly impossible to study.

However, in April, two sets of researchers separately detected the first such signal radiating from within our own galaxy. It was pinned to an explosion of activity on a distant magnetar.

"What's really surprising is that we saw anything at all from our own galaxy, given how rare these extragalactic FRBs are," Christopher Bochenek, a graduate student at the California Institute of Technology and the lead author of one of the new studies, said in a press briefing. "We didn't have to wait 50 years to detect a fast radio burst in the Milky Way. We only had to wait a few."

The signal was about 1,000 times weaker than the typical FRB from outside our galaxy. But the fact that a magnetar can produce such a burst at all shows that these dead stars could be the source of all FRBs.

An explosion of X-rays and gamma rays with just one radio burst

Because the fast radio burst detected in April was within our galaxy, and because it was clearly linked to a magnetar, astronomers could study the non-radio emissions that accompanied the event. Bochenek's team found that it came with a burst of X-rays.

A third team of researchers also connected the new FRB to an outpouring of gamma-ray emissions from the same magnetar. The group detected 29 such gamma-ray bursts in less than one hour. But only one of them brought the radio burst with it.

That suggests that in "only a small fraction of magnetar bursts — maybe one out of 100, even one out of 1,000 — these X-ray bursts make FRBs," Bing Zhang, an astrophysicist on the Chinese team that detected the gamma rays, said in the briefing.

It's still unclear how the radio bursts are related to X-ray and gamma-ray outbursts, but there's plenty more research to come. Last month, astronomers detected even more FRBs coming from the same dead star.

"It's really exciting," Deborah Good, an astronomer studying the magnetar and its FRBs at the University of British Columbia in Canada, told ScienceAlert. "I'm optimistic that as we study these bursts more carefully, it will help us better understand the potential relationship between magnetars and fast radio bursts."