Global centres in a class of quintic polynomial differential systems

A centre of a differential system in the plane R² is an equilibrium point p having a neighbourhood U such that U \ is filled with periodic orbits. A centre p is global when R² \ is filled with periodic orbits. In general, it is a difficult problem to distinguish the centres from the foci for a given class of differential systems, and also it is difficult to distinguish the global centres inside the centres. The goal of this paper is to classify the centres and the global centres of the following class of quintic polynomial differential systems {align*} ẋ= y, ẏ={-}x+a₀₅\,y^5+a₁₄\,x\,y^4+a₂₃\,x^2\,y^3+a₃₂\,x^3\,y^2+a₄₁\,x^4\,y+a₅₀\,x^5, {align*} in the plane R² .