A Novel Physical Interpretation of Spectral Index Observations on Event Horizon Scales of M87 Based on the Light Primitive Theory

On July 20, 2026, a team from the Shanghai Astronomical Observatory, in collaboration with the EHT and GMVA arrays, conducted dual-band millimeter-wave observations at 1.3 mm and 3.5 mm, and obtained the first spatially resolved spectral index map of the compact object at the centre of M87 on event horizon scales. Observations clearly show that the spectral index near the central region is positive, gradually decreases radially outwards and turns negative, and the spectral index transition interface highly coincides with the jet origin region. The mainstream academic community adopts the ADAF accretion flow synchrotron radiation model to interpret the observational results. However, its theoretical premise assumes that plasma charged particles exist in the central region for a long time, which creates an irreconcilable inherent contradiction with the material stability under the extreme high temperature of trillions of Kelvin. Based on the Light Primitive Theory, this paper establishes a layered physical model of reversible phase transition between photons and physical particles. The central region of M87 presents a three-layer gradient structure analogous to the Earth’s core, mantle and crust. The innermost ultra-high-temperature core is a region purely consisting of high-energy gamma photons without any observable charged particles; the middle layer serves as a phase transition transition layer where photons and particles coexist; the outermost layer is dominated by physical charged particles, with only a small amount of gamma photons permeating outwards. From the inside out, the temperature gradually decreases, the proportion of photons declines, and the proportion of particles rises. Millimeter-wave spectra can only be generated by charged particles, so the pure-photon core region cannot be detected via millimeter waves. This observational blind zone precisely confirms the physical feature that the core contains no physical particles and is based on high-density gamma photons. The quasi-collimated through channels at the two poles form genuine jets, while local light transmission in other directions only produces diffuse overflow radiation without the structural characteristics of jets. Instead of pursuing instantaneous high-precision layer sizes, this paper aims to establish a long-term inheritable observation standard for celestial bodies applicable over hundreds of millions of years. Joint millimeter-wave and gamma-ray observations in the future can infer layer boundaries, monitor the increase or decrease of core energy, and judge the overall expansion or contraction evolution trend, providing a brand-new theoretical framework and observation paradigm for long-term research on the celestial evolution at the centre of M87.