AI 中文总结
该研究利用GMVA与EHT的观测数据，得到M87*事件视界尺度首张空间分辨光谱指数图，检测到径向梯度，为区分黑洞辐射及喷流模型提供了观测约束。
AI 中文摘要
近邻射电星系M87中心的超大质量黑洞（M87*）是研究黑洞物理的核心目标。事件视界尺度的空间分辨光谱测量可揭示辐射起源，并探测黑洞近邻的等离子体与引力环境。本研究基于2018年利用包含ALMA、格陵兰望远镜的全球毫米VLBI阵列（GMVA）及事件视界望远镜（EHT）获取的3.5毫米（86吉赫兹）和1.3毫米（230吉赫兹）近同时高分辨率图像，开展光谱特性分析，得到了致密区域（≤100微角秒）内首张空间分辨光谱指数图（$S_\nu \backsim \nu^\beta$）。研究进一步检测到显著的径向梯度：在内部约20微角秒处（略小于1.3毫米环）光谱指数呈小幅上升，随后在更大半径处系统下降；在约30微角秒（接近3.5毫米环半径）处，光谱指数由正值转为负值，这与最内吸积流中依赖频率的同步辐射不透明度一致。这些结果提供了新的观测约束，有助于区分M87*视界尺度辐射及相对论性喷流产生的模型。
英文摘要
The supermassive black hole at the center of the nearby radio galaxy M87 (M87*) is a prime target for studying black hole physics. Spatially resolved spectral measurements on event-horizon scales can reveal the origin of the emission and probe the plasma and gravitational environment in the immediate vicinity of the black hole. Here, we present an analysis of spectral properties based on nearly simultaneous high-resolution images at 3.5 mm (86 GHz) and 1.3 mm (230 GHz), obtained in 2018 with the Global Millimeter VLBI Array (GMVA) including ALMA and the Greenland Telescope, and the Event Horizon Telescope (EHT). We obtain the first spatially resolved spectral-index map ($S_ν\propto ν^α$) within the compact region ($\leq 100\,μ$as). We further detect a robust radial gradient with a modest rise in the inner $\lesssim 20~μ$as (slightly inside the 1.3 mm ring), followed by a systematic decline at larger radii. The spectral index transitions from positive to negative values near $\sim 30~μ$as, close to the 3.5 mm ring radius, consistent with frequency-dependent synchrotron opacity in the innermost accretion flow. These results provide new observational constraints that can help discriminate between models of the horizon-scale emission and the launching of relativistic jets in M87*.
Journal refAstrophysical Journal Letters, 1006, L24 (2026)
