Astrophysics and Cosmology

1. Astrophysics and Cosmology Lecture #26 Lecture XXVI

2. Concepts • Parsec, light year • Curved space • Hubble’s law • Big Bang • Early universe Lecture XXVI

3. Units to measure large distances • Light second = cx1s=3x108 m = 3x105 km • Earth circumference = 40,000 km = 0.13 light seconds • Earth – Moon = 1.28 light seconds • Light minute = cx60s=1.8x1010 m • Earth – Sun = 8.3 light minutes • Earth – Pluto = 311 light minutes • Light year = cx1y=9.46x1015 m Lecture XXVI

4. Scales of the universe Distance from Earth • Proxima Centauri (next door neighbor) – 4.3 ly • Center of our Galaxy (Milky Way) 3x104 ly • Our galaxy (Milky Way) is a disk • D=100,000 ly thickness 2,000ly total number of stars in Milky Way ~1011 • Nearest galaxy (Andromeda nebula) 2x106 ly • Farthest galaxies 1010 ly Lecture XXVI

5. How to measure heavenly distances? f D d q Cannot clock the light, cannot use a ruler… Parallax – apparent motion of a star against the background of more distant stars f=90-q D=d/tan(f) d=1.5x108km Parallax angle in seconds – distance to the star in Parsec = 3.26 ly Lecture XXVI

6. Other information from the sky • Apparent brightness  on average related to distances • Spectrum  temperature • Red shift – related to relative velocity  distances • High energy radiation • Neutrinos (m=~0, weak interaction) – propagate great distances • Experiment  observation • SLOAN digital sky survey: http://skyserver.fnal.gov/en/ • Hubble telescope: http://www.stsci.edu/ftp/science/hdf/hdf.html Lecture XXVI

7. Hubble deep field Lecture XXVI

8. Hertzsprung-Russel (H-R) diagram • Luminosity increases with star’s mass • Temperature related to the wavelength lT=2.9x10-3mK • By measuring l we can find T, then using H-R diagram we can predict the absolute brightness (L). • The apparent brightness (l) is related to L and the distance to the star: Lecture XXVI

9. Evolution of the stars-I • Stars are born when gaseous clouds (mostly hydrogen) contract due to gravity • Gravity accelerates the particles of the star inward  kinetic energy is increasing, could be large enough (1keV~107K) to overcome coulomb repulsion and start nuclear fusion HHe (In our Sun – yellow dwarf) • Pressure from the energy released in fusion keeps the star from collapsing • When the hydrogen in the core burns out the core contracts and T goes up  the outer envelope expands and cools down (Red giant) • The core continues to heat up and He starts burning in fusion and continue to higher Z’s ending nucleosynthesis at Fe and Ni • No pressure from fusion – gravitational collapse – white dwarf • Pauli principle for orbital e keeps the star from further collapse • T goes down white draft becomes black dwarf (cloud of ash) Lecture XXVI

10. Evolution of the stars-II • Heavier stars continue to burn beyond Fe and Ni in endoergic reactions • In addition the following process can occur e-+pn+n Neutrons are formed in abundance – neutron star (>~1.5 mass of Sun, D~10km) Pauli principle for neutrons limit the size No electrostatic repulsion – leads to a catastrophic collapse – supernova explosion If mass of neutron star >2-3xSolar mass – black hole – not even light can escape Lecture XXVI

11. Gravity and curvature of space • Einstein’s general relativity: No observer can determine by experiment if he is accelerating or is rather in a gravitational field • Explain gravity (interaction) through curvature of space (geometry) • Establish equivalence between gravitational and inertial mass • Experimental proof: Curving light: straight line becomes curved in gravitational field • Extreme curvature – black hole: black because not even light can escape it Lecture XXVI

12. Expanding universe • Redshift – spectral lines shifted – object is moving • In 1929 Edwin Hubble, measured the redshifts of a number of distant galaxies. the redshift of distant galaxies increased as a linear function of their distance • Hubble’s law v=Hd • v- velocity of galaxies, d – distance • H=80km/s/Mpc • The universe is expanding. Lecture XXVI

13. Age of the universe v=Hd • v- velocity of galaxies, d – distance • H=80km/s/Mpc = 20km/s/million ly • Farthest galaxy 1010ly • t=d/v=d/(dH)=1/H=15x109yr Lecture XXVI

14. Universe evolution Age of the universe 1010 years Cosmic Microwave background – echo of the Big Bang Lecture XXVI

15. Cosmic microwave background • Discovered in 1964 by Arno Penzias and Robert Wilson as a “noise” in radio telescope • Cosmic microwave background at l=7.35 cm • Blackbody radiation at T=~3K • Present precise measurement 2.7K • Echo of the Big Bang, predicted in 1940 by George Gamow • Radiation “decoupled” from matter when atoms were formed and there were no free electrons to scatter light (~3000K, 0.3 Myears after birth) Lecture XXVI

16. Fate of the Universe • Gravity slows down the expansion • Depending on the density the universe might • Continue to expand infinitely • Collapse back to a point Lecture XXVI

17. WMAP Launched from cape Canaveral on June 30 2001 Lecture XXVI

18. Trajectory Lunar swingby Phasing loops Official arrival date: Oct 1, 2001 100 days to L2, 1.5e6 km from Earth. Lecture XXVI

19. COBE 1992 Bennett et al 2003 WMAP 2003 Lecture XXVI

20. Facts first, then the conclusions! Lecture XXVI

21. BEYOND LCDM model FLATNESS Riess et al. 2001 + HST meas. of Ho de Bernardis et al 2000 Verde et al 2002 (Spergel et al 2003) Lecture XXVI After

22. We (and all of chemistry) are a small minority in the Universe. Compare gravitational rotation of galaxies with luminous matter Lecture XXVI