Transcript www.astro.utu.fi

Future Universe
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what is the evolution
of the universe on
very long timescales?
first, a review of our
progress so far
Hot big bang model
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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
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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
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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
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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
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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
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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
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Andromeda is headed this
way!
Galaxy and Andromeda
eventually combine to form
elliptical galaxy after few
10s billion years
Fate of Galaxy II
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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.htm
l
Fate of Galaxy III
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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!
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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/in
dex.html
Black holes get bigger
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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
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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
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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
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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?
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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
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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
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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
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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
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neutrinos
photons
electrons
positrons
formation of positronium
'atoms'?
radius order 1012 Mpc
decay time of order
10116 years
dark energy may
change this picture
Positronium 'atom'
Source: www.stolaf.edu/academics/positron/intro.htm
Credit
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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/