The Astrophysical Future


+1 Gyr: Evolution of the sun makes Earth inhospitable for life




Equilibrium temperature of a planet scales as the temperature of the star, so as the Sun becomes more luminous and hotter, the Earth warms up as well:



We will need to move away to the outer solar system.


+ 4-6 Gyr: Milky Way and Andromeda collide and merge


The 3D motion of Andromeda is still not well-known, but most recent estimates say first collision in ~4 Gyr (~ 30kpc impact), followed by a merger at about 6 Gyr. Example (figures from van der Marel+ 2012):






But what will it look like?

+5 Gyr: Sun evolves through red giant phase, becomes a white dwarf




Need to have colonized other stars by then!


+10-50 Gyr: Galaxies run out of hydrogen gas, star formation shuts down:


Depletion time = Mgas/SFR

For a galaxy like the Milky Way, Mgas ~ 5x109 Msun, SFR ~ 1 Msun/yr, depletion time ~ 5 Gyr.

Why is this a low estimate? What could increase this number?


+ 50-100 Gyr: Galaxy groups and clusters merge to form the most massive galaxies



+ trillion (1012) years: lowest mass stars (~0.08 Msun) die out


At this point, all that is left are dark remnants:
  • Brown dwarfs
  • White dwarfs
  • Neutron stars
  • Black holes
Nothing shines except during collisions.


Now what?



The even more distant future


+1018 yrs: planets detached from parent stars?


Repeated encounters with other stars slowly add energy to planetary orbits, eventually they become unbound.

+ 1020 yrs: (some) stars leave galaxies?


Close 3-body encounters between stars eject some stars from galaxy.

+ 1065 yrs: stellar black holes evaporate?

+ 10100 yrs: supermassive black holes evaporate?

Somewhere along the way:

  • Dark matter annihilation?
  • Proton decay?
The universe is all energy, and it's all redshifted to longest wavelengths. zzzzzzzz.....