Into the Dark: The Long Term Future of our Dying Universe

Professor Fred Adams

This talk outlines astrophysical issues related to the long term fate of the cosmos. We consider the evolution of planets, stars, stellar populations, galaxies, and the universe itself over time scales that greatly exceed the current age of the universe. The discussion starts with the effects of accelerated cosmic expansion, which causes every galaxy cluster to become its own island universe in the near future. Next we discuss stellar evolution calculations that follow the development of the low mass stars (the most common stars) and consider the end of conventional star formation. We then determine the mass distribution of stellar remnants--the neutron stars, white dwarfs, and brown dwarfs remaining after stellar evolution has run its course. After several trillion years, the supply of interstellar gas grows depleted, yet star formation continues at a highly attenuated rate through brown dwarf collisions. This process tails off as the galaxy gradually loses its stars by ejecting the majority, and driving a minority toward accretion onto massive black holes. As the galaxy disperses, weakly interacting dark matter particles are accreted by white dwarfs, where they subsequently annihilate and keep the old stellar remnants relatively warm. After accounting for the demise of the galaxy, we consider the evaporation of expelled degenerate objects (planets, white dwarfs, and neutron stars). The evolution and eventual sublimation of these objects is dictated by the decay of their constituent nucleons. After white dwarfs and neutron stars have disappeared, the black holes are the brightest astrophysical objects, slowly losing their mass as they emit Hawking radiation. After the largest black holes have evaporated, the universe slowly slides into darkness.