Future Universe

what is the evolution of the universe on very long time-scales?

first, a review of our progress so far

Hot big bang model

10-43 sec Planck time, four forces united

10-35 sec quarks dominate universe 10-12 sec strong force splits from

weak and electromagnetic forces 0.01 sec electrons and positrons 1 sec Universe becomes

transparent to neutrinos 3 min protons and neutrons form H

and Helium nuclei 300,000 years neutral atoms form

Hot big bang model

100 million years first stars form 1 billion years first galaxies form 2-4 billion years stars of the halo

of Milky Way form circa 4 billion years disk of

galaxy begins to form 9 billion years Sun and Earth

form

Stellar evolution

stars burn H to He, He to heavier elements

stars like the Sun are now middle aged

low mass stars will burn for much longer, 1013 years

about half of all stars are “low mass” stars

Hipparcos colour magnitude diagram

Stellar evolution

convection dominates the evolution, as most of the Hydrogen becomes accessible to the core burning

stars turn into Helium white dwarfs, without going to the giant branch

then they slowly fade from view

Laughlin, Bodenheimer and Adams 1997

Gas supply runs out

low mass stars dominate after the gas supply runs out, as no new stars are created

galaxy currently gets a few solar masses of gas per year, which dilutes the ISM

metals and Helium will build up nicely

H = 20%, He = 60%, metals = 20%

leads to shorter stellar lifetimes

Simple infall model of Galactic chemical evolution in the Solar Cylinder (Flynn)

Fate of the Earth

Sun goes to giant branch in few billion years

will the Earth spiral in to the Sun, or spiral outwards from it (and survive)?

currently uncertain, as predictions depend on unclear physics of stellar “mass loss”

In any case, it will boil the planet after about 2 billion years The planet "V 391 Pegasi b" as it survives the red giant

expansion of its dying sun. Image: HELAS, the European Helio- and Asteroseismology Network.

Fate of Galaxy I

Andromeda is headed this way!

Galaxy and Andromeda eventually combine to form elliptical galaxy after few 10s billion years

Fate of Galaxy II

Dynamical relaxation --although it has been insignificant for the Galaxy so far, stars eventually undergo close encounters

stars eventually acquire escape velocity, and evaporate from the galaxy

time scales for typical galaxies are of order 1019 years

similar process for galaxy clusters

Dissolving galaxies surrounded by vast halos of evaporated stars.

abyss.uoregon.edu/~js/ast123/lectures/lec26.html

Fate of Galaxy III

Gravitational radiation--- orbits of stars left in the central parts of the Galaxy will eventually decay

for a star like the Sun, the decay timescale is of order 1024 years

the few stars which were not ejected eventually settle in the Galactic core, merging with a supermassive blackhole

Gravitational radiation detection in the binary pulsar of Taylor and Hulse

New stars!

Occasionally, the dim night sky will be lit up by a new star

brown dwarf or white dwarf binaries merging and starting to burn again

collisions or merging via gravitational radiation are the mechanisms at work

time scale of order 1022 years for collisions (the faster of the two!) Modelling of stellar collisions by Joshua Barnes

www.ifa.hawaii.edu/~barnes/research/stellar_collisions/index.html

Black holes get bigger

Milky Way has a central black hole

time scale for all stars in galaxy to merge with it via collisions is 1030 year

most stars avoid this fate by evaporating from the galaxy

Orbit of one star around the central black hole in the Galaxy (ESO)

www.eso.org/public/outreach/press-rel/pr-2002/pr-17-02.html

Fate of dark matter

dark matter, if it is particles, might decay into radiation

WIMPS are a popular dark matter candidate particle, with mass of order 10 - 100 GeV

perhaps they annihilate when they collide

Big Bang models constrain the interaction rate

time scale for annihilation of order 1022 years

end of dark matter halos

Dark matter simulation of the Milky Way halo, by Jurg Diemand and Piero Madau (University of California)

Dark matter captured by stars

dark matter particles might get captured in stellar interiors

200 km/s speed of dark matter, compared to escape speed from white dwarf of order 3000 km/s

most stars will be extremely dim white dwarfs

capture timescale of order 1025 years

White dwarfs in a globular cluster as seen by the Hubble Space Telescope

Dark matter as stellar fuel

The white dwarfs capture WIMPS, which eventually annihilate, providing energy

White dwarfs glow hotter and brighter than they otherwise would, at the toasty temperature of 60 K

entire galaxy glows with same luminosity as Sun!

this fuel source will eventually run out too, and stars begin to fade

Does ordinary matter decay?

Do protons decay? GUTs predicts they might,

and decay on a timescale great than 1032 years, and up to 1041 years

At the decay time, most protons will be in the nearly dead white and brown dwarfs (“black dwarfs”)

new source of fuel! all stars radiate away after

a few hundred decay timescales

Inside the proton (Wikipedia)

Proton powered white dwarfs

proton decay releases 235 MeV photons, which are thermalised in the WD core and released at the surface as black body radiation

luminosity of WD is of order 10-24 Lsun or about 400 Watts!

Lgal of order 10-13 Lsun! WD surface temperature 0.06 K (which is

extremely hot compared to the background radiation)

Hawking radiation and BHs

Hawking radiation predicted for black holes

timescales for BHs to radiate away goes like their mass

million solar mass black holes (like now at the Galactic center) take 1083 years to dissapear

1012 solar mass black holes (equivalent to expected mass of Milky Way) and would take 10101 year to dissapear

Background radiation

CMB and starlight dominate the present background light

CMB is redshifted away as the universe expands

stellar radiation will soon dominate the CMB

dark matter annihilation will dominate when ordinary stars burn out

then proton decay and finally

BH radiation

DCMB (grey) compared to intensity of extragalactic background light (green), which peaks in the IR and far-IR. The CMB dominates the starlight by about a factor of 10.www.astro.ucla.edu/~wright/CIBR/

Cosmic composition 10100 years

neutrinos photons electrons positrons formation of positronium

'atoms'? radius order 1012 Mpc decay time of order

10116 years dark energy may

change this picturePositronium 'atom'Source: www.stolaf.edu/academics/positron/intro.htm

Credit

this talk is closely based on the article “A dying universe – the long term fate and evolution of astrophysical objects” by Adams and Laughlin

http://arxiv.org/abs/astro-ph/9701131/