The Event Horizon Telescope (EHT), an international collaborative research project, reobserved the shadow and ring of light structure of the supermassive black hole in M87 and uncovered new properties.
Kim Jae-young, a professor in the Department of Physics at Ulsan National Institute of Science and Technology (UNIST), and Park Jong-ho, a professor in the Department of Space Science at Kyunghee University, together with the Event Horizon Telescope (EHT) international collaborative team that includes the Korea Astronomy and Space Science Institute (KASI), said on the 16th that they confirmed the magnetic field pattern of the supermassive black hole at the center of the M87 galaxy, taken over four years since 2017, had flipped. The findings were published on the 16th in the international journal Astronomy & Astrophysics.
EHT is a virtual Earth-sized telescope created by linking radio telescopes scattered around the world and is the core of an international cooperation project to capture images of black holes. The event horizon refers to the boundary that separates the inside and outside of a black hole. The EHT team continued observations from 2017 through 2018, 2021, 2022, 2024, and 2025.
The black hole observed this time is the supermassive black hole of the giant elliptical galaxy M87 in the Virgo Cluster, about 55 million light-years (light-year: the distance light travels in one year, about 9.46 trillion km) from Earth. It exceeds 6 billion times the mass of the sun.
In 2021, the team analyzed M87 black hole data and found that while the central shadow and ring shape remained the same, the light polarization pattern indicating the direction of the magnetic field had changed significantly. Compared with the 2017 image, the polarization direction was the exact opposite.
The team suggested that the magnetic field near the M87 black hole structurally changed, or that matter such as plasma might have influenced it. This is evidence that the magnetic field and matter near the event horizon are far more dynamic than expected and undergo complex motions.
Professor Park Jong-ho said, "It was completely unexpected that the polarization pattern reversed direction between 2017 and 2021," and added, "It is a major challenge to existing models and shows that there is still much we do not know about the vicinity of the event horizon."
Professor Kim Jae-young, a member of the EHT Science Council who set research goals and directly participated in data analysis, said, "Around the event horizon, hot, high-pressure plasma plunges into or erupts from the black hole in an instant," and noted, "This flow seems to stir the surroundings and create polarization changes. Understanding this phenomenon will require more precise research beyond existing models."
The team also captured signals from the starting point of the "jet," an ultrafast particle beam that emerges from a supermassive black hole at nearly the speed of light. M87's jet affects star formation and the energy distribution of the galaxy and plays an important role in cosmic evolution.
In 2026, the EHT team plans to capture the world's first black hole video by imaging M87 twice a week for about three months, and the Korea VLBI Network (KVN) will participate in the project. While they previously obtained roughly one black hole image per year, next year they aim to capture one image every two weeks.
Professor Kim added, "Every year, we continue to advance with telescope expansion, equipment upgrades, and new algorithms," and said, "Going forward, we will link space and ground, and ground and lunar surface radio telescopes to image more distant black holes."
References
Astronomy & Astrophysics (2025), DOI: https://doi.org/10.1051/0004-6361/202555855