Download The birth and evolu\on of galaxies, stars

The birth and evolu0on of galaxies, stars and planets Peter Johansson Department of Physics, University of Helsinki Arkadia and the WDC Pavilion Helsinki, June 15th, 2012 1.  Galaxies: A large system consis0ng of stars, gas and dust surrounded by a dark maJer halo. 2.  Stars: A massive luminous sphere of plasma in hydrosta0c equilibrium (gravity <-­‐> gas pressure) producing fusion energy. 3.  Planets: An object that is massive enough to be round, but not massive enough for nuclear fusion. Dominates its orbit around the parent star. The Universe at age 380,000 years, corresponding to z=1100. T
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5 Today galaxies: δ~106 and galaxy clusters: δ~103 •  How did all the structures form from the small density inhomogenei0es present in the cosmic microwave background (CMB)? •  The period immediately a^er the forma0on of the CMB is called the dark ages of the Universe. •  During this period there are no stars and galaxies, instead the Universe is filled by neutral hydrogen and helium gas that is slowly cooling due to the expansion of the Universe. •  The dark ages end when the first stars are formed from the 0ny overdensi0es seeded in the early Universe. The first stars form about 300-­‐500 million years a^er the Big Bang, corresponding to z≈20-­‐30. Size of the density perturba0on is increasing -­‐> Size of the Universe is increasing-­‐> •  In an expanding Universe with only baryons (ordinary maJer) the density perturba0on Δ does not have enough 0me to grow to the galaxies we see today -­‐> we need dark maJer to explain the existence of galaxies. Len0cular galaxies are intermediate between spirals and ellip0cals in that they have a disk, but no spiral structure and low levels of gas and young stars. Ellip0cal galaxies are elongated massive stellar systems, with liJle gas and lots of old red stars. Spiral galaxies have a disk with gas and young blue stars, in the centre a central bulge with old red stars can be found. Pozee et al. (2010) •  The local galaxy popula0on is observed to be bimodal: Galaxies above ≈Milky Way mass are red spheroidal systems and below blue, star-­‐forming disk galaxies. •  Some mass-­‐dependent process must turn off star forma0on and make the galaxies dead and red. Galaxy Merger simula0ons: Research performed at the University of Helsinki. Cosmological galaxy simula0ons: Simula0on showing stars: Simula0on showing gas: Movie Credits: Phil Hopkins, University of Berkeley •  The most important factor in defining the evolu0on of a star is its mass. •  High-­‐mass stars are very bright and shortlived (a few million years). •  Intermediate mass stars, such as the sun live for 10 billion years. •  Low-­‐mass red dwarf stars live for 100s of billions of years. Movie Credits: Thomas Greif, MPA •  The inner 4 planets have high densi0es (rocky-­‐metallic composi0on) and the outer 4 planets are (gaseous). •  Link to the forma0on scenario of planets. 1.  Core accre0on model: Planets grow from small seeds (overdensi0es) in the protoplanetary disk through collisions. 2.  Disk instability model: The protoplanetary disk undergoes a global gravita0onal instability and the planets are formed rapidly on rela0vely short 0mescales. hJp://www.cfa.harvard.edu/iau/Anima0ons/Anima0ons.html 1. 3. RM
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Hot Jupiters: Most detected exoplanets are hot Jupiters, i.e. very massive gaseous planets orbi0ng very close to their central stars. Lower mass planets: So far most of the lower mass planets discovered are similar to Neptune, i.e. gaseous/icy planets. However, there is some tenta0ve evidence for Earth-­‐
mass planets from transit surveys. The first through Earth analogue will probably be detected within 10 years. 1.  Galaxies: A large system consis0ng of stars, gas and dust surrounded by a dark maJer halo. –  The forma0on of galaxies requires dark maJer. Galaxies come mainly in two types. Star-­‐forming blue disk-­‐like galaxies and old red and dead ellip0cal galaxies. 2.  Stars: A massive luminous sphere of plasma in hydrosta0c equilibrium (gravity <-­‐> gas pressure) producing fusion energy. –  Stars form from giant molecular clouds through gravita0onal collapse. Massive stars live short lives ending in supernova, lower mass stars live longer. 3.  Planets: A object that is massive enough to be round, but not massive enough for nuclear fusion. Dominates its orbit around the parent star. –  Planets form in protoplanetary disks around stars. The solar system is quite regular and stable, but it differs in composi0on drama0cally when compared to other nearby detected extrasolar systems.