For 10 years now, astronomers have been picking-up unusual blasts of high-energy radio waves from distant parts of the cosmos. Each transmission of these “fast radio bursts” has the energy of millions of stars for a fleeting moment, before they disappear in just a fraction of a second. Yet, the source of these powerful signals has scientists baffled.
“We don’t know what type of object is making them,” admits Keith Bannister, an astronomer at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Sydney, Australia. “We don’t have a clue – you click your fingers and they’ve come and gone.”
Astronomers first detected fast radio bursts in 2007, using data from the Parkes radio telescope in Australia, and, so far, more than 20 bursts have been discovered. The mystery of what they are has become one of the hottest topics in astronomy.
This week, research published in the journal Nature has, for the first time, identified where one of these bursts came from. The international team used the giant Arecibo radio telescope in Puerto Rico, along with radio telescopes in Mexico and Europe, to hone in on the source of the signal: a small galaxy 2.5 billion light years away.
Bannister’s team, meanwhile, has recently published a study on the brightest burst yet seen. “This one almost punched our eyes out but because it was so bright,” he says. The burst was so intense it allowed the astronomers to study the space the transmission passed through by measuring its interaction with the electrons it encountered along the way.
“We were able to directly measure the magnetic field between galaxies and see how much material it’s gone through,” says Bannister. “This is one of the wonders of radio astronomy, you can learn so much from something that’s over in a blink of an eye.”
Neither of these new discoveries, however, tackles the fundamental question about fast radio bursts: what are they? The answer could give us a whole new insight into the nature of the Universe.
“It may turn out to be something simple,” Maxim Lyutikov of Purdue University in the US told BBC Earth last year. “But indeed it may turn out to be a window into new physics, and into new astrophysical events and phenomena.”
One hypothesis is that they are caused by the ultimate death stars; another theory blames defects in the fabric of spacetime
One popular hypothesis is that fast radio bursts are the result of hypothetical phenomena known as blitzars – cataclysmic scenarios of stellar destruction. Blitzars are imagined to be high energy pulsars – rotating dead stars emitting a regular beacon of electromagnetic radiation – being consumed by a black hole…the ultimate death stars.
“The fact that something like a blitzar could exist is mind-blowing and raises all kinds of questions,” says Sheila Kanani from the Royal Astronomical Society in London. “How were they created? Where does the energy come from? What does it mean for the evolution of the Universe?”
An alternative idea is that these blasts of energy result from some sort of massive cosmic explosion – maybe neutron stars colliding. “A lot of energy is being released to make a burst,” says Bannister. “But what’s really interesting is that when we look with other telescopes, we don’t see anything that’s obviously the aftermath of an explosion.” Nor would it explain why some bursts repeat over a period of several days.
“It could,” Bannister says, “be something to do with a black hole and, by the time we’ve looked, the black hole’s swallowed it or it could be a type of explosion that we don’t see with other telescopes – we just have no idea.”
Perhaps more intriguing is a theory that these high-energy blasts represent defects in the nature of the fabric of space-time. This hypothesis supposes that the Universe has cosmic strings stretching across it, conducting electrical current. When they snap, the strings explode in a burst of electromagnetic radiation.
Fast radio bursts could even be aliens, beaming a signal across space. Scientists aren’t ruling it out.
Until I know what they are, I wouldn’t say they’re not space aliens - Keith Bannister
“Until I know what they are, I wouldn’t say they’re not space aliens,” Bannister says, surprisingly. “Unless I have a measurement to the contrary, it’s a possibility.”
“It’s probably unlikely,” he adds. “What we’re seeing with the way the radio signal drops away is very similar to what a natural phenomenon might do – if I were an alien it would be a bad way of doing it.”
Now that astronomers are able to identify galaxies the transmissions come from, the next stage is to zoom in on the exact source. If, for example, the bursts originate from the centre of a galaxy, they are likely to be associated with black holes. If they come from the periphery, they could be emitted from an explosion on a star or planet.
The quest to unravel the mystery of these strange cosmic signals demonstrates just how far we have to go before we fully understand the Universe. “It shows we are always learning and willing to hold up our hands and say we don’t really know,” says Kanani. “That’s a really important lesson for future scientists.”
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