Researchers at the Shanghai Astronomical Observatory (SHAO) have successfully created the first dual-frequency spectral-index map of the black hole in galaxy M87. By combining data from the Event Horizon Telescope and the Global Millimeter Very Long Baseline Interferometry (VLBI) Array, the team determined how plasma properties and radiation evolve near the event horizon, offering a new method to study jet formation and accretion flows.
Mapping Plasma Physics Near the Event Horizon
The transition from capturing static images to analyzing the physical state of matter near a black hole marks a shift in radio astronomy. In a study published in The Astrophysical Journal Letters, scientists utilized data captured at both 1.3 mm and 3.5 mm wavelengths. This dual-frequency approach allowed the team to map the spectral index—a measurement of how radiation intensity changes with frequency—across the region surrounding the M87 black hole.
According to the findings, the spectral index is positive in the innermost regions, which indicates that synchrotron self-absorption is significantly impacting the emission. As the distance from the black hole increases, the index shifts to negative values. This transition occurs at approximately 30 μas, a distance that matches the radius of the ring-like structure observed at 3.5 mm. Dr. ZHAO Shanshan, first author and assistant researcher at SHAO, noted that this mapping allows for the quantitative characterization of radiation properties, providing a clearer look at how plasma behaves in strong gravitational fields.
Did you know?
The “ring” seen in black hole imagery is not just a visual artifact. Researchers suggest this structure is intimately tied to the physical state of the plasma circulating near the event horizon.
Future Trends in Multi-Frequency VLBI Imaging
The success of the dual-frequency study sets a precedent for future observations in high-resolution astronomy. The research team emphasizes that expanding these techniques to include more frequencies and higher sensitivity will be critical for future progress. By disentangling plasma physics from gravitational signatures, astronomers expect to gain a more granular understanding of how black holes consume matter and launch high-energy jets.
Dr. LU Rusen, a researcher at SHAO and corresponding author, stated that multi-frequency, horizon-scale imaging will allow for more precise studies of strong-field gravity.
Frequently Asked Questions
- Why is a dual-frequency image better than a single-frequency image?
A dual-frequency image allows scientists to calculate the spectral index, which helps distinguish between different physical processes like synchrotron radiation and absorption, revealing the state of the plasma. - What is the significance of the 30 μas transition point?
This distance aligns with the 3.5 mm ring structure, confirming that the visual features of the black hole are direct indicators of the underlying plasma physics. - Who funded this research?
The study was supported by the National Natural Science Foundation of China, China’s National Major Science and Technology Projects, the Chinese Academy of Sciences (CAS), and the Shanghai Municipal Government.
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