Astronomers have achieved a major breakthrough by detecting a hidden magnetic signal from one of the most powerful explosions in the universe.
Using the U.S. National Science Foundation’s Very Large Array (VLA) radio telescope, researchers observed polarized radio waves from a gamma-ray burst for the first time.
They also made the first detection of a phenomenon called Faraday rotation in one of these explosions, giving scientists an entirely new way to study the intense magnetic fields surrounding these extraordinary events.
The research, led by scientists from the University of Arizona and the University of Utah, opens a new window into the extreme physics behind gamma-ray bursts, or GRBs.
Gamma-ray bursts are the brightest and most energetic explosions known in the universe. In just a few seconds, a single burst can release as much energy as the Sun will produce during its entire lifetime.
Scientists believe these events occur when massive stars collapse at the end of their lives or during other catastrophic cosmic events, launching narrow jets of particles that travel at nearly the speed of light.
These jets continue to produce a radio afterglow that can remain visible for months after the initial explosion.
Although astronomers have studied gamma-ray bursts for decades, measuring the magnetic fields around them has been extremely difficult. Those magnetic fields are believed to play a crucial role in forming and powering the powerful jets, but until now they have largely remained hidden.
The newly studied burst, called GRB 260310A, occurred relatively close to Earth by astronomical standards. Its radio afterglow was among the brightest seen in decades, giving researchers a rare opportunity to examine it in exceptional detail.
When the team pointed the Very Large Array toward the fading explosion, they discovered that the radio waves were polarized. This means the light waves were vibrating mainly in one direction instead of randomly. A familiar example of polarization occurs when sunlight reflects off water, which is why polarized sunglasses can reduce glare.
The discovery became even more significant when the researchers noticed that the polarization changed depending on the radio wavelength being observed. This effect, known as Faraday rotation, happens when polarized light passes through a cloud of charged particles threaded with magnetic fields. As the light travels, its direction of polarization twists. The amount of twisting reveals valuable information about the strength and structure of the magnetic fields along its path.
The measurements showed magnetic fields that were thousands of times stronger than could be explained by our own Milky Way or the space between galaxies. Instead, the evidence points to an extremely dense and highly magnetized cloud of gas surrounding the star before it exploded.
The researchers believe this cloud was an HII region, a large bubble of ionized hydrogen gas created by intense ultraviolet radiation and powerful stellar winds from young, massive stars. Finding the burst inside such an environment strengthens the idea that many gamma-ray bursts are produced when the universe’s most massive stars reach the end of their lives.
According to the researchers, previous attempts to detect polarization in gamma-ray bursts relied mainly on shorter radio wavelengths and had to be made very soon after the explosion before the afterglow faded. The new observations show that longer radio wavelengths can also reveal valuable information, including the first direct measurement of Faraday rotation in a gamma-ray burst.
The team believes future observations with the Very Large Array and other radio telescopes will allow scientists to watch how magnetic fields around gamma-ray bursts change over time.
This could greatly improve our understanding of how these enormous explosions generate powerful jets, release vast amounts of energy and shape some of the most extreme environments anywhere in the universe.
Source: National Radio Astronomy Observatory.
