Shanghai Astronomical Observatory Maps M87 Black Hole Radiation Properties

Decoding Black Hole Plasma Physics

While the M87 black hole—weighing 6.5 billion times the mass of the Sun—became famous for the first-ever image of a black hole captured in 2019, previous efforts were limited to single-frequency observations. To move beyond mere imaging, the team led by SHAO collaborated with international partners to conduct a dual-frequency joint analysis. By combining 2018 observational data from the Event Horizon Telescope and the Global Millimeter Very Long Baseline Interferometry (VLBI) Array at 1.3 mm and 3.5 mm, the researchers mapped how radiation changes with distance from the black hole center.

According to News, this spectral index map serves as a crucial probe for understanding the radiation processes within accretion flows and jets. Dr. LU Rusen, a researcher at SHAO and the study’s corresponding author, stated that multi-frequency imaging allows scientists to disentangle plasma physics from gravitational signatures, leading to more precise studies of strong-field gravity.

For more on this story, see Shanghai Astronomical Observatory Maps Plasma Behavior Near M87 Black Hole.

Mapping Radiation Gradients

The study reveals that radiation properties vary systematically based on the distance from the black hole. In the innermost regions, the spectral index is positive and shows a slight increase with radius, which indicates that the emission is significantly influenced by synchrotron self-absorption. As the distance increases, the spectral index transitions from positive to negative values, marking a shift toward an optically thin emission regime.

A key finding of the research is that this transition occurs at approximately 30 microarcseconds (μas) from the center. This distance aligns with the radius of the ring-like structure observed at 3.5 mm. As noted by Phys.org, this alignment suggests that the ring-like structure is not just a morphological feature but is intrinsically linked to the physical state of the plasma near the event horizon.

Future Implications for Astrophysics

Dr. ZHAO Shanshan, an assistant researcher at SHAO and the first author of the study, emphasized the importance of this quantitative approach. "By obtaining the first spatially resolved spectral-index distribution of the M87 black hole, we can quantitatively characterize how the radiation properties change across the region surrounding the black hole," Zhao said. This data provides new clues for researchers attempting to model the complex mechanics of accretion flows and the formation of jets.

This follows our earlier report, M87* Black Hole Study Maps Plasma Physics Using Dual-Frequency Images.

The project was supported by several institutions, including the National Natural Science Foundation of China, China’s National Major Science and Technology Projects, the Chinese Academy of Sciences, and the Shanghai Municipal Government. Looking ahead, the team expects that continued advancements in millimeter VLBI technology will facilitate observations at additional frequencies with greater sensitivity. These future developments are expected to provide deeper insights into the extreme gravitational environments surrounding black holes.