The Event Horizon Telescope continues to improve its observational capabilities. Years of observations have captured evolving polarization patterns around a supermassive black hole and detected 230 GHz radiation at the base of its jet. These new findings reveal the dynamic environment around the M87* black hole and deepen scientists' understanding of black hole physics.
The Event Horizon Telescope (EHT) collaboration has released a new image of the supermassive black hole at the center of the M87 galaxy, revealing the temporal evolution of polarized radiation near the black hole. Scientists also discovered for the first time in EHT data the presence of extended radiation connecting the black hole's ring structure to the base of its jet. These latest findings, published in the journal Astronomy & Astrophysics on September 16, offer new insights into the physical processes occurring in the extreme environment surrounding black holes.
The M87 galaxy is approximately 55 million light-years from Earth, and its central black hole is over 6 billion times more massive than our sun. The EHT, an "Earth-sized telescope" comprised of a global network of radio telescopes, released its first image of a black hole in 2019, which was taken in 2017, with polarization results released in 2021. Now, by comparing observational data taken in 2017, 2018, and 2021, scientists have made new progress in revealing the time-varying nature of the black hole's magnetic field.
New images released by the Event Horizon Telescope (EHT) collaboration reveal a dynamic environment surrounding the supermassive black hole M87*, exhibiting a constantly changing pattern of magnetic field polarization. As shown in the image, the white line indicates the direction of the electric field vector of the observed electromagnetic waves, which is perpendicular to the magnetic field in that local region. The image shows that the magnetic field distribution near M87* was counterclockwise from the inside out in 2017 (left), remained essentially the same in 2018 (center), and reversed to a clockwise pattern in 2021 (right).
The study found that between 2017 and 2021, the polarization direction flipped: the magnetic field distribution near M87* was counterclockwise from inside to outside in 2017, remained basically the same in 2018, and then reversed to a clockwise direction in 2021. The cumulative effect of this change in magnetic field direction over time indicates that M87* and its surrounding environment are in a state of continuous evolution.
The researchers believe that this apparent change in polarization rotation may stem from the combined effects of the internal magnetic structure and external effects, such as Faraday shields. The evolution of polarization reflects the turbulent environment surrounding the black hole, where magnetic fields play a key role in how matter falls into the black hole and how it releases energy outward.
"Amazingly, the ring size remained consistent over four years, confirming the black hole shadow predicted by Einstein's general theory of relativity, but its polarization pattern changed significantly," said Paul Tiede, an astronomer at the Harvard-Smithsonian Center for Astrophysics and co-leader of the study. "This suggests that the magnetized plasma near the event horizon is far from static, but is constantly changing and extremely complex, pushing the limits of our current theoretical models."
"The reversal of the polarization direction over the four years from 2017 to 2021 was completely unexpected," explained Jongho Park, an astronomer at Kyung Hee University and a collaborator on the project. "This not only challenges existing models, but also shows that there are still many things near the event horizon that humans do not yet understand."
Ultra-energetic jets like those in M87 play a crucial role in galactic evolution by regulating star formation and large-scale energy distribution. These powerful jets produce a full range of electromagnetic radiation, including gamma rays and neutrinos, providing a unique laboratory for studying the formation mechanisms of extreme cosmic phenomena. This latest discovery provides a crucial piece in this puzzle.
Notably, the 2021 observations included the addition of two telescopes: the Kitt Peak telescope in Arizona, USA, and the NOEMA array in France. This significantly enhanced the sensitivity and image clarity of the EHT, enabling scientists to successfully constrain the direction of radiation from the base of M87's relativistic jet, which is moving away from the black hole at near the speed of light. Furthermore, performance upgrades to the Greenland Telescope and the James Clerk Maxwell Telescope (JCMT) further improved data quality.
"Year after year, we've expanded and enhanced the EHT by adding new telescopes, improving instrument performance, and developing new algorithms," added Michael Janssen, one of the collaborators and a member of the EHT Science Committee, Assistant Professor at Radboud University Nijmegen in the Netherlands. "This achievement exemplifies the scientific breakthrough resulting from these multiple enhancements. The new scientific questions it has stimulated will undoubtedly guide our exploration for years to come."
Shen Zhiqiang, a researcher at the Shanghai Astronomical Observatory, said, "We have been involved in many aspects of technological innovation, such as cutting-edge multi-frequency simultaneous reception, raw data correlation processing, frequency and phase transfer calibration and mapping technology, and have promoted related scientific breakthroughs."
