Supermassive Black Hole Growth in a Cosmology with a Time-Varying Cosmological Constant

The existence of supermassive black holes (SMBHs) within the first 800 million years after the Big Bang remains difficult to explain and is still under active debate. At the same time, a dynamical vacuum energy density has been proposed as a possible solution to the cosmological coincidence problem. It is therefore natural to explore its implications for black hole evolution. In this work, we study the rapid growth of SMBHs in a decaying-vacuum cosmology with a time-dependent cosmological constant. In this framework, black holes can grow at rates far exceeding the Eddington limit, which can be phenomenologically described as an effective conversion of vacuum energy into black hole mass. This mechanism may offer a new perspective on the formation and early growth of SMBHs.