Astronomers have hypothesized that cosmic magnetic fields might flow through the jets, helping them form and providing structural support.
To obtain the measurements of these magnetic fields, the international team employed a novel trick. They observed the jets in linearly polarized light, which is sensitive to the size of magnetic field patches. Larger magnetic field patches, for example, produce more polarized light.
On January 14, 2019, a flash of gamma rays triggered NASA's Swift satellite, which alerted astronomers of the burst's location in the direction of the constellation Fornax. The astronomers then used the Atacama Large Millimeter/Submillimeter Array (ALMA) telescope in Chile to search for radio waves from the explosion, which occurred more than 4.5 billion years ago in a galaxy 7 billion light-years away.
The team detected a subtle, but revealing, polarization signal of 0.8 percent, implying magnetic field patches about the size of our solar system.
Next, the researchers will combine this new information with data from X-ray and visible light telescopes.
"The lower frequency data from the Very Large Array (VLA) in New Mexico helped confirm that we were seeing the light from the jet itself rather than from the interaction of the jet with its environment," said Kate Alexander, a NASA Einstein Fellow who led the VLA observations.
"Magnetic fields are ubiquitous but notoriously difficult to constrain in our universe," said Wen-fai Fong, an assistant professor of astrophysics at NU Weinberg College of Arts and Sciences. "The fact that we have been able to detect their presence, let alone in the fastest jets we know of, is an incredible and storied feat of observation."
Gamma ray bursts produce powerful jets that travel close to the speed of light and shine with the incredible luminosity of more than a billion suns combined. Because these jets are extremely bright at radio wavelengths, the discovery of polarized radio signals may offer new clues to help solve this mystery. Polarization is a property of light that indicates how a magnetic field is organized and structured in a jet.
The research, posted on NU's website on Wednesday, was published last week in The Astrophysical Journal Letters.