Deep space radio waves originated from a surprising source

Fast radio bursts (FRBs) are extraordinary, fleeting explosions of radio waves. These signals, often originating from neutron stars or black holes, last for just a millisecond but carry immense energy, briefly surpassing the brightness of entire galaxies.

Since their first detection in 2007, astronomers have identified thousands of these bursts, originating from distances as vast as 8 billion light-years away. However, their exact sources have remained an enigma.

A breakthrough study by MIT researchers, published in the journal Nature, sheds new light on this cosmic puzzle.

By examining FRB 20221022A, a signal detected 200 million light-years away, the team pinpointed its origin near a highly magnetized neutron star.

The findings provide the first concrete evidence that some FRBs emerge from the magnetosphere – the chaotic, magnetic region surrounding such stars.

Understanding neutron stars — the basics

When a massive star runs out of fuel and goes supernova, the core that’s left behind can collapse into a super-dense ball called a neutron star.

These stars are so dense that a teaspoon of neutron star material could weigh about as much as Mount Everest.

What makes them even more fascinating is that they’re mostly made up of neutrons – subatomic particles that normally hang out inside the nucleus of atoms.

The incredible pressure from the collapsing star pushes electrons and protons together to form these neutrons, making the star ridiculously dense and compact.

Neutron stars can spin incredibly fast, sometimes up to several hundred times per second. And they have intense magnetic fields, which can generate beams of radiation that shoot out from their poles.

If one of these beams happens to point toward Earth, we get a glimpse of a phenomenon called a pulsar. This makes the neutron star appear to “pulse” as it spins, like a cosmic lighthouse.

Despite being small in size, neutron stars pack a punch with their gravitational pull, and they can even warp space-time around them, causing weird effects like time dilation.

Decoding the twinkle of fast radio bursts

To trace the origins of FRB 20221022A, the researchers employed a technique called scintillation. This phenomenon, which is akin to the twinkling of stars, occurs when light from a small, bright source passes through gas, causing variations in brightness.

The team analyzed the FRB’s brightness fluctuations and discovered that the burst originated from an extremely compact region, no more than 10,000 kilometers wide.

“This means that the FRB is probably within hundreds of thousands of kilometers from the source,” explained study lead author Kenzie Nimmo.

“That’s very close. For comparison, we would expect the signal to be tens of millions of kilometers away if it originated from a shockwave.”

Energy released from magnetic fields

The team’s analysis revealed that FRB 20221022A likely exploded from a region just 10,000 kilometers away from a neutron star – a distance comparable to the span between New York and Singapore. This proximity strongly suggests that the burst emerged from the neutron star’s magnetosphere.

“In these environments of neutron stars, the magnetic fields are really at the limits of what the universe can produce,” said Nimmo. “There’s been a lot of debate about whether this bright radio emission could even escape from that extreme plasma.”

“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,” noted Kiyoshi Masui, an MIT associate professor of physics.

Elusive origins of fast radio bursts

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has significantly advanced our understanding of FRBs. Since 2020, this unique radio telescope array has detected thousands of bursts.

However, the origins of these bursts have remained elusive due to competing theories. Some suggest FRBs arise from the turbulent magnetosphere near compact objects, while others propose they originate from far-out shockwaves.

The scintillation analysis by the MIT team rules out the latter possibility for FRB 20221022A. Instead, their findings confirm the burst’s origin within a magnetically chaotic environment, reinforcing the role of neutron stars as central players in producing FRBs.

Polarization: Another key insight

In a companion study, researchers from McGill University observed a highly polarized signal from FRB 20221022A.

This polarization traced a smooth S-shaped curve, reminiscent of signals from pulsars, which are magnetized, rotating neutron stars.

“To see a similar polarization in fast radio bursts was a first,” the McGill team reported. This evidence supported the MIT team’s scintillation-based conclusion that the burst’s origin was in the immediate vicinity of the neutron star.

Milestone in understanding fast radio bursts

The precision of this study is staggering. The team successfully traced the FRB’s origin to a region just 10,000 kilometers wide – a feat akin to measuring the width of a DNA helix from the moon.

“There’s an amazing range of scales involved,” said Masui.

These findings mark a milestone in understanding FRBs. By combining scintillation techniques with CHIME’s vast dataset, scientists can now pinpoint the origins of other bursts with unprecedented accuracy.

“These bursts are always happening, and CHIME detects several a day,” noted Masui. “There may be a lot of diversity in how and where they occur, and this scintillation technique will be really useful in helping to disentangle the various physics that drive these bursts.”

Extreme physics and magnetic fields

The research was made possible by support from numerous institutions, including the Canada Foundation for Innovation, the Dunlap Institute for Astronomy and Astrophysics, and the Trottier Space Institute.

The study’s MIT co-authors, along with collaborators from multiple institutions, have paved the way for deeper insights into the enigmatic world of fast radio bursts.

As scientists continue to unravel these cosmic phenomena, the universe’s most brilliant radio flares may hold the key to understanding extreme physics and magnetic fields at the edge of what the cosmos can produce.

The study is published in the journal Nature.

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