Download - Future Universe
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/