The universe is full of mysteries, and one of its most captivating phenomena is the existence of supermassive black holes that produce powerful jets of high-energy particles, creating sources of extreme brightness in space.
When these jets are aligned with Earth, they give rise to an astronomical marvel known as a blazar. An international group of astrophysicists published new findings from IXPE about a blazar called Markarian 421 this week.
NASA's IXPE Unravel Blazar Secrets
To unravel the secrets of these high-speed jets and the particles within them, scientists turn to NASA's IXPE (Imaging X-ray Polarimetry Explorer), a cutting-edge space observatory launched in December 2021.
IXPE is equipped with three identical telescopes, which are intended to measure the polarization of cosmic X-rays of black holes, neutron stars, and pulsars.
Located in the constellation Ursa Major, approximately 400 million light-years away from Earth, the Markarian 421 blazar revealed an unexpected and fascinating feature: a helical magnetic field structure in the part of the jet where particles are being accelerated.
Lead author Laura Di Gesu, an astrophysicist from the Italian Space Agency, expressed the team's excitement, saying, "Markarian 421 is an old friend for high-energy astronomers."
"We were sure the blazar would be a worthwhile target for IXPE, but its discoveries were beyond our best expectations, successfully demonstrating how X-ray polarimetry enriches our ability to probe the complex magnetic field geometry and particle acceleration in different regions of relativistic jets," she added.
According to NASA, blazar jets can extend millions of light-years in length and emit intense brightness as particles approach the speed of light. They release tremendous energy and behave in ways that Einstein predicted.
The Doppler effect amplifies their brightness, making blazars appear brighter than all stars in their galaxies. Despite extensive research over decades, scientists have yet to fully comprehend the physical processes governing blazar jets' dynamics and emissions.
However, IXPE's X-ray polarimetry has provided an unprecedented view of these enigmatic celestial objects, offering essential insights into their physical structure and emission mechanisms.
Unexpected Findings
Conventional research models depict the powerful jet outflows as spiraling helix structures similar to how human DNA is organized. However, the unexpected finding in Markarian 421's jet was the presence of regions where shockwaves are accelerating particles.
IXPE's observations of Markarian 421 in May and June 2022 revealed surprising variability in the polarization angle. Scientists had anticipated some changes in the polarization direction, but the magnitude of the rotations was more significant than previous optical observations of many blazars had suggested.
The team planned several observations of the blazar, with the first showing a constant polarization of 15%. Initially, when analyzing IXPE's polarization data, there was a sudden drop to zero between the first and second observations.
However, upon further examination, it became evident that the polarization remained steady while its direction underwent a U-turn, rotating almost 180 degrees within a span of two days.
This intriguing phenomenon persisted during the third observation, with the direction of polarization continuing its rotation at the same rate. Markarian 421's helical magnetic field offers clearer evidence of a shockwave, exciting astrophysical jet studies with IXPE's observations.
