Researchers study accretion radiation from supermassive black holes in quasars

By studying the optical and ultraviolet radiation produced by the accumulation of supermassive black holes at the centers of quasars, Associate Professor Cai Zhenyi and Professor Wang Junxian from the Department of Astronomy at the University of Science and Technology of China (USTC) belongs to the Chinese Academy of Sciences. Science (CAS) discovered that the spectral energy distribution does not depend on the quasar’s internal brightness. The study shows a significant deviation in the average energy distribution of quasars in the ultraviolet spectrum compared to that predicted by classical accretion disk theory.

The results were published online on October 5, 2023 in the journal Nature Astronomy. The research of associate professor Cai Zhenyi and professor Wang Junxian focuses directly on the spectral energy distribution from optical to ultraviolet emission of large quasar samples. The study uses observational data from the ground-based SDSS telescope and the GALEX space telescope.

Scientists have discovered that the average energy distribution in the ultraviolet spectrum of quasars does not depend on their internal brightness. Differences in intrinsic brightness cannot explain the Baldwin effect. This research also challenges the predictions of standard accretion disk theory. At the same time, the researchers propose a new possible physical origin of the Baldwin effect: brighter quasars have weaker accretion disk temperature fluctuations, which does not allow the creation of clouds with more emission lines.

Additionally, this study corrects for the effects of absorption from the intergalactic medium and reveals that the average ultraviolet spectrum of quasars is lighter than previous studies had claimed. This difference poses a serious problem for the standard accretion disk model, but is in good agreement with predictions from a model that includes accretion disk winds. The results of this study have broad implications in better understanding various aspects of the physics of supermassive black hole accretion, black hole mass evolution, cosmic reionization, etc.