For ten years, astronomers have been collecting unusual bursts of high-energy radio waves from distant parts of space. Each transmission of these "fast radio bursts" has the energy of millions of stars for an instant before disappearing in a split second. Yet scientists are concerned about the source of these powerful signals.
"We don't know what kind of object creates them," admits Keith Bannister, a Commonwealth Scientific Industrial Research Astronomer (CSIRO) in Sydney, Australia. "We have no idea - you snap your fingers and they come and go."
Astronomers first recorded fast radio bursts in 2007 using data from the Parks radio telescope in Australia, and have since detected more than 20 such bursts. The mystery of their origin has become one of the hottest topics in the field of astronomy.
Last week, a study appeared in the journal Nature for the first time, which determined where these bursts may come from. An international team of scientists used the giant Arecibo radio telescope in Puerto Rico, as well as radio telescopes in Mexico and Europe, to pinpoint the source of the signal: a tiny galaxy 2.5 billion light-years away.
Bannister's team, meanwhile, recently published a study on some of the brightest bursts ever seen. “This one almost made its way to our eyes, it was so bright,” he says. The flash was so intense that it allowed astronomers to study the space through which the transmission passed by measuring interactions with electrons along the way.
“We were able to directly measure the magnitude of the magnetic field between galaxies and see how much material the flare went through,” Bannister says. "This is one of the wonders of radio astronomy: you can get a ton of information from even the most fleeting event."
But these new discoveries do not answer the fundamental question about fast radio bursts: what are they? The answer to this question could give us a completely new understanding of the nature of the universe.
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“It could be something completely simple,” says Maxim Lyutikov of Purdue University in the US. "But it can also open a window to new physics, to new astrophysical phenomena and events."
One popular hypothesis is that fast radio bursts are the result of hypothetical phenomena known as blitzars - cataclysmic scenarios of the destruction of stars. The blitzars are thought of as high-energy pulsars - rotating dead stars that shimmer with a beacon of electromagnetic radiation - that are being swallowed up by a black hole … truly death stars.
"The fact that a blitz can exist is dizzy in itself and raises all sorts of questions," says Sheila Kanani of the Royal Astronomical Society in London. “How were they created? Where does energy come from? What does this mean for the evolution of the Universe?"
An alternative idea is that these bursts of energy were the result of some kind of massive cosmic explosion - possibly a collision of neutron stars. “A lot of energy is released to make a splash,” says Bannister. "But what's really interesting is that when we look through our telescopes, we don't see any obvious afterword of any kind of explosion." There is also nothing to explain that some of the bursts are repeated for certain periods of several days.
“Perhaps they have something to do with the black hole, and when we begin to peer, the black hole engulfs the object; or it's a type of explosion that we don't see with telescopes - we just don't know."
Perhaps a more interesting theory would be that these high-energy bursts represent defects in the nature of the fabric of spacetime. According to this hypothesis, cosmic strings are stretched through the Universe, which conduct electric currents. When they break, the strings explode in bursts of electromagnetic radiation.
The fast radio bursts could even be explained by aliens sending signals across space. Scientists do not exclude this possibility.
"Until I know for sure, I won't write off the possibility of aliens," Bannister says. “Until I prove otherwise, anything is possible. Though unlikely. We see that this radio signal is weakening in the same way as natural phenomena usually do - in which case it is a bad way of communication for aliens."
Now that astronomers can identify the galaxies from which transmissions are coming, the next step is to determine the exact source. If, for example, the bursts come from the center of the galaxy, they are likely to be associated with black holes. If they come from the periphery, they can be emitted from the explosion of a star or planet.
The quest to unravel the mystery of these strange cosmic signals shows how far we must go before we fully understand the universe. “This shows that we are always ready to learn and admit that some things we do not know. And this is an important lesson for scientists of the future."
ILYA KHEL