Scientists pin down the origins of a fast radio burst

Since the discovery of the first fast radio burst (FRB) in 2007, astronomers have detected thousands of FRBs ranging from within our own galaxy to as far away as 8 billion light-years away. Exactly how these cosmic radio flares are emitted remains a hotly debated unknown.

Now, MIT astronomers have determined the origin of at least one FRB using a new technique that can do the same for other FRBs. In their new study, which appears in the journal naturethe team focused on FRB 20221022A—a previously discovered fast radio burst detected in our galaxy about 200 million light-years away.

The team further determined the precise location of the radio signal by analyzing its “scintillation,” similar to the twinkling of stars in the night sky. Scientists studied changes in the brightness of FRBs and determined that the bursts must have originated near their source, rather than farther away, as some models predicted.

The research team estimates that FRB 20221022A exploded very close to the rotating neutron star, up to 10,000 kilometers away. That’s shorter than the distance between New York and Singapore. At such close range, the bursts are likely to originate from the neutron star’s magnetosphere – a highly magnetic region immediately surrounding an ultra-compact star.

The team’s discovery provides the first conclusive evidence that fast radio bursts may originate from the magnetosphere, the high magnetic field environment immediately surrounding extremely compact objects.

“In these environments of neutron stars, the magnetic fields are really at the limit of what the universe can produce,” said lead author Kenzie Nimmo, a postdoc at MIT’s Kavli Institute for Astrophysics and Space Studies. “There is a lot of debate about whether this bright radio emission can escape from extreme plasmas.”

“Atoms cannot exist around these highly magnetic neutron stars, also known as magnetars—they would just be torn apart by the magnetic field,” said Kiyoshi Masui, associate professor of physics at MIT. “Excitingly, we found The energy stored in the magnetic field close to the source is being twisted and reconfigured so that it can be released in the form of radio waves that we can see on the other side of the universe.”

MIT co-authors of the study include Adam Lanman, Shion Andrew, Daniele Michilli and Kaitlyn Shin, as well as collaborators from multiple institutions.

Burst size

The detection of fast radio bursts has increased in recent years thanks to the Canadian Hydrogen Intensity Mapping Experiment (CHIME). The radio telescope array consists of four large fixed receivers, each shaped like a half-pipe, tuned to detect radio emissions in a range that is highly sensitive to fast radio bursts.

Since 2020, CHIME has detected thousands of FRBs from all over the universe. While scientists generally believe the bursts are caused by extremely dense objects, the exact physics driving FRBs is unknown. Some models predict that FRBs should originate from the turbulent magnetosphere immediately adjacent to dense objects, while others predict that these bursts should originate farther away as part of a shock wave that propagates away from the central object.

To distinguish between the two cases and determine where FRBs occur, the team considered scintillation – an effect that occurs when light from small, bright sources such as stars passes through certain media, such as galactic gas. As starlight passes through the gas, it bends, making it appear to a distant observer as stars twinkling. The smaller or further away an object is, the more it flickers. Light from larger or closer objects, such as the planets in our solar system, bends less and therefore does not flicker.

The team reasoned that if they could estimate the extent of a FRB’s scintillation, they could determine the relative size of the region where the FRB originated. The smaller the region, the closer the burst is to its source, and the more likely it is that it came from a magnetically turbulent environment. The larger the area, the farther away the bursts are, supporting the idea that FRBs originate from distant shock waves.

flashing pattern

To test their idea, the researchers studied FRB 20221022A, a fast radio burst detected by CHIME in 2022. However, the team’s collaborators at McGill University discovered that FRB 20221022A exhibited one outstanding property: the burst of light was highly polarized, with the polarization angle following a smooth S-shaped curve. This pattern has been interpreted as evidence that the FRB emission site is rotating – a feature previously observed in pulsars, which are highly magnetized rotating neutron stars.

This is the first time that similar polarization has been observed in a fast radio burst, suggesting that the signal may be generated near a neutron star. The McGill team’s findings are published today in a companion paper nature.

The MIT team realized that if FRB 20221022A originated near a neutron star, they should be able to use scintillation to prove it.

In their new study, Nimmo and her colleagues analyzed data from CHIME and observed sharp changes in brightness that mark flickers—in other words, FRBs are flashing. They confirmed that there is gas somewhere between the telescope and the fast radio burst that is bending and filtering radio waves. The team then located the location of this gas, confirming that gas within the FRB’s host galaxy was responsible for some of the observed flickers. The gas acted as a natural lens, allowing researchers to zoom in on the FRB site and determine that the burst originated from an extremely small region, estimated to be about 10,000 kilometers across.

“This means that FRBs may be hundreds of thousands of kilometers away from their source,” Nimmo said. “That’s pretty close. For comparison, we expected that if the signal originated from a shock wave, it would be over tens of millions of kilometers away, and we wouldn’t see any flicker at all.”

“Zooming in from a distance of 200 million light-years to an area of ​​10,000 kilometers is like being able to measure the width of a DNA helix on the surface of the moon, which is about 2 nanometers wide,” Masui said. “The range of scales involved is staggering.”

The team’s results, combined with the McGill team’s findings, rule out the possibility that FRB 20221022A emerged from the outer reaches of a compact object. Instead, these studies demonstrate for the first time that fast radio bursts can originate very close to a neutron star in a highly chaotic magnetic environment.

“These outbreaks happen all the time, and CHIME detects them several times a day,” Masui said. “There can be a lot of diversity in how and where they occur, and this flicker technique will be very useful in helping to unravel the various physical phenomena that drive these bursts.”

The research was supported by several institutions, including the Canada Foundation for Innovation, the University of Toronto’s Dunlap Institute for Astronomy and Astrophysics, the Canadian Institute for Advanced Research, McGill University’s Trottier Institute for Space Studies, and the University of British Columbia.