CAMBRIDGE, Mass. -- Every day, several times a day, massive explosions of radio waves burst forth from distant corners of the universe, each carrying more energy than our sun produces in a month. While thousands of these fast radio bursts have been detected, their origins have remained elusive -- until now, thanks to an innovative approach that uses the universe's own distortions as a magnifying glass.
These cosmic fireworks, known as fast radio bursts (FRBs), can briefly outshine entire galaxies despite lasting for just a thousandth of a second. Since their discovery in 2007, astronomers have detected them everywhere from our own galaxy to as far as 8 billion light-years away. Their precise origins have sparked intense debate in the scientific community.
Now, an international team led by MIT researchers has found compelling evidence about these bursts' origins by studying a burst dubbed "20221022A," located in a galaxy about 200 million light-years from Earth. Their detective work, published in the journal Nature, relied on a phenomenon called scintillation -- the same effect that makes stars appear to twinkle in the night sky.
Just as Earth's atmosphere causes starlight to flicker, clouds of electrons in space cause radio waves to scatter and interfere with each other, creating distinctive patterns in signals reaching our telescopes. The smaller or more distant an object is, the more it "twinkles." By analyzing this twinkling pattern, astronomers can determine the size and location of the burst's source, similar to how an astronomer might deduce a star's properties from its shimmer.
The researchers detected two different scales of this scattering in FRB 20221022A's radio waves: one caused by material in our own Milky Way galaxy, and another from matter near the burst's source. Through careful analysis, they determined the emission region must be extremely compact -- approximately 10,000 kilometers across, less than the distance between New York and Singapore.
"In these environments of neutron stars, the magnetic fields are really at the limits of what the universe can produce," explains lead author Kenzie Nimmo, a postdoc in MIT's Kavli Institute for Astrophysics and Space Research, in a statement. "There's been a lot of debate about whether this bright radio emission could even escape from that extreme plasma."
This compact size challenges theories suggesting FRBs are produced far from their source objects. Such models typically predict the fast radio bursts should originate tens of millions of kilometers away. Instead, the results strongly support the idea that FRBs are generated within or just beyond the magnetosphere, which is the region dominated by a neutron star's powerful magnetic field.
The environment around these highly magnetic neutron stars, known as magnetars, is so extreme that atoms cannot exist - they would be torn apart by the intense magnetic fields. "The exciting thing here is, we find that the energy stored in those magnetic fields, close to the source, is twisting and reconfiguring such that it can be released as radio waves that we can see halfway across the universe," says Kiyoshi Masui, associate professor of physics at MIT.
Making these measurements required exceptional precision and sophisticated analysis techniques. The team used the Canadian Hydrogen Intensity Mapping Experiment (CHIME), which comprises four large, stationary half-pipe-shaped receivers tuned to detect radio emissions within a frequency range that is highly sensitive to fast radio bursts. Since 2020, CHIME has detected thousands of FRBs within this optimal detection range, with several new discoveries each day.
The research demonstrates how astronomical scintillation, often considered a nuisance that blurs our view of the cosmos, can actually serve as a powerful tool for probing the physics of these enigmatic events. The precision achieved is remarkable. As Masui notes, "Zooming in to a 10,000-kilometer region, from a distance of 200 million light years, is like being able to measure the width of a DNA helix, which is about 2 nanometers wide, on the surface of the Moon."
From a region only 10,000 kilometers wide surrounding a distant neutron star, across 200 million light-years of intergalactic space, to the sophisticated detectors of the CHIME telescope, the journey of these radio waves (and our understanding of them) showcases how far astronomy has come. As we continue to detect several bursts each day, each flash provides new evidence about how the intense magnetic fields in neutron star magnetospheres can produce some of the universe's most spectacular radio bursts.