Using NSF’s Very Large Array (VLA), astronomers achieved a groundbreaking wireless detection of polarization and Faraday rotation in the afterglow of a gamma-ray burst, unveiling unprecedented insights into the magnetic fields surrounding one of the universe’s most powerful explosions.

This figure illustrates Faraday rotation in the afterglow of a gamma-ray burst. The powerful jet (top left) emits polarized radio waves through the thin walls of the surrounding magnetized gas bubble, known as the HII region. As light traverses this material, its polarization angle is affected by the magnetic field. Longer wavelengths experience a more pronounced effect, causing red and blue waves to oscillate in different directions. This information allows astronomers to map the magnetic landscape surrounding GRB 260310A for the first time. Image credit: NSF / AUI / NRAO / M. Weiss

Gamma-ray bursts are among the most powerful explosions in the universe, releasing as much energy in mere seconds as the sun does over its entire lifespan.

These extraordinary events are believed to propel thin jets of particles that accelerate to nearly the speed of light, producing radio afterglows that can persist for months.

Despite extensive research, accurately measuring the magnetic fields associated with these jets and their environments remains a significant challenge.

The gamma-ray burst under investigation, GRB 260310A, is relatively close to Earth by cosmic standards and features one of the brightest radio afterglows detected in decades, providing astronomers with an exceptional opportunity.

By targeting the fading explosion with the VLA, astronomer Tanmoy Laskar and his team at the University of Utah observed polarized radio waves, indicating that light waves are oscillating in a preferred direction, akin to how polarized sunglasses filter sunlight.

Additionally, they identified a variation in the polarized signal with wavelength, a phenomenon termed Faraday rotation.

This groundbreaking detection, previously unrecorded in gamma-ray bursts, functions like a magnetic fingerprint, revealing critical data about the strength and structure of the magnetic field that the light traverses.

Much like a prism bends different colors of visible light variably, a magnetized plasma can alter the polarization angle of radio waves.

The rate of change in polarization with wavelength indicates the strength of the magnetic field encountered by the light.

“Gamma-ray bursts represent the universe’s most powerful explosions, and magnetic fields are believed to play a crucial role in fueling them, yet studying these fields has proven to be complex,” Laskar explained.

“The detection of polarized radio emissions now enables us to measure the magnetic environment surrounding one of the most violent phenomena in the cosmos.”

“With our new gamma-ray burst observations, we can utilize space as a laboratory to validate our understanding of physics in extreme conditions.”

The VLA data indicated that the magnetic field along the light’s trajectory is thousands of times stronger than that observed in our Milky Way galaxy and intergalactic space.

Instead, this data reveals a denser, magnetized cloud of gas enveloping the star that erupted to create GRB 260310A.

This cloud, identified as the HII region, is an ionized hydrogen gas bubble sculpted by the intense ultraviolet radiation and stellar winds from massive young stars.

The proximity of GRB 260310A to such a region aligns with theories suggesting that gamma-ray bursts originate from the most massive stars, enhancing our comprehension of the star types and environments that trigger these extreme events.

“Previous efforts to detect polarization in gamma-ray bursts employed facilities like the Atacama Large Millimeter/Submillimeter Array (ALMA), focusing on shorter wavelengths at earlier stages before the afterglow faded,” noted Colin Christie, a graduate student at the University of Arizona.

“Using the VLA, we’ve shifted into the centimeter band to achieve the first-ever measurement of Faraday rotation in a gamma-ray burst.”

“Each new observation uncovers another layer of the magnetic narrative these explosions convey.”

“In the future, continuous monitoring of gamma-ray burst afterglows with the VLA and other radio telescopes will enable scientists to track the evolution of the magnetic field structure in real time,” remarked Kate Denham Alexander from the University of Arizona.

“This capability could revolutionize our understanding of how relativistic jets form, are powered, and how their magnetic energy is released in the universe’s most extreme environments.”