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

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Presentation on theme: "Future Universe what is the evolution of the universe on very long time- scales? first, a review of our progress so far."— Presentation transcript:

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, 10 13 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 10 19 years similar process for galaxy clusters Dissolving galaxies surrounded by vast halos of evaporated stars. l

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 10 24 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 10 22 years for collisions (the faster of the two!) Modelling of stellar collisions by Joshua Barnes dex.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 10 30 year most stars avoid this fate by evaporating from the galaxy Orbit of one star around the central black hole in the Galaxy (ESO)

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 10 22 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 10 25 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 10 32 years, and up to 10 41 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 10 83 years to dissapear 10 12 solar mass black holes (equivalent to expected mass of Milky Way) and would take 10 101 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.

20 Cosmic composition 10 100 years neutrinos photons electrons positrons formation of positronium 'atoms'? radius order 10 12 Mpc decay time of order 10 116 years dark energy may change this picture Positronium 'atom' Source:

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

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