A dying universe: The long-term fate and evolution of astrophysical objects

Abstract

This paper examines the long-term evolution of astrophysical objects on planetary, stellar, galactic, and cosmological scales. The authors begin by extending standard stellar evolution calculations to follow the future evolution of low-mass M-type stars, which dominate the stellar mass function. They derive scaling relations to describe how the range of stellar masses and lifetimes depends on the future increase in metallicity. The authors proceed to determine the ultimate mass distribution of stellar remnants, including neutron stars, white dwarfs, and brown dwarfs, which defines the “final stellar mass function.” They argue that the supply of interstellar gas will be exhausted after a few trillion years, but star formation will continue at a very low rate through collisions between brown dwarfs. They discuss the ultimate fate of the galaxy, arguing that the galaxy will gradually disperse as its stars are ejected into intergalactic space, with a minority accreting onto a central black hole. The authors then consider the fate of the expelled degenerate objects (planets, white dwarfs, and neutron stars) in the context of proton decay, examining the eventual sublimation of these objects as their constituent nucleons decay. Finally, the authors consider cosmological issues arising from the long-term evolution of the universe, including the relation between future density fluctuations and the prospects for continued large-scale expansion. They compute the evolution of the background radiation fields of the universe, showing how the radiation background will be dominated by stars, dark-matter annihilation, proton decay, and black holes after several trillion years. – AI-generated abstract