PHYSICS AND ASTRONOMY COLLOQUIUM
Tuesday, March 20, 2001
4:10pm, Room 118 PA

INTO THE DARK: The long term fate and evolution of 
astrophysical objects in a dying universe

Fred C. Adams, Physics Department, University of Michigan 

Abstract: This talk outlines astrophysical issues related to the long
term fate of the universe.  We consider the evolution of planets,
stars, stellar populations, galaxies, and the universe itself over
time scales which greatly exceed the current age of the cosmos. This
discussion starts with new stellar evolution calculations which follow
the future development of low mass (M type) stars that dominate the
stellar IMF.  We then determine the final mass distribution of stellar
remnants -- the neutron stars, white dwarfs, and brown dwarfs
remaining at the end of stellar evolution. After 1--10 trillion years,
the supply of interstellar gas becomes exhausted, yet star formation
continues at a highly attenuated level through brown dwarf collisions.
This process tails off as the galaxy gradually depletes 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 with each other and thereby keep the old stellar remnants
relatively warm. After accounting for the destruction of the galaxy,
we consider the fate of the expelled degenerate objects (planets,
white dwarfs, and neutron stars) within the assumption that proton
decay is a viable process.  The evolution and eventual sublimation of
these objects is dictated by the decay of their constituent nucleons,
and this evolutionary scenario is developed in some detail.  After
white dwarfs and neutron stars have disappeared, galactic black holes
slowly lose their mass as they emit Hawking radiation.  After the
largest black holes have evaporated, the universe slowly slides into
darkness.