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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

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Future Universe

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  1. Future Universe • what is the evolution of the universe on very long time-scales? • first, a review of our progress so far

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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)

  7. 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.

  8. Fate of Galaxy I • Andromeda is headed this way! • Galaxy and Andromeda eventually combine to form elliptical galaxy after few 10s billion years

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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)

  14. 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

  15. 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

  16. 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)

  17. 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)

  18. 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

  19. 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/

  20. 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 picture Positronium 'atom' Source: www.stolaf.edu/academics/positron/intro.htm

  21. 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/

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