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Astronomy: The Universe HONORS 227 FALL 2005 20 October 2005 Dr. Harold Geller From the past... • “…How is it possible by any methods of observation yet known to the astronomer to learn anything about the universe as a whole? It is possible only because the universe, vast though it is, shows certain characteristics of a unified and bounded whole. …science shows unity in the whole structure, and diversity only in details.” » Simon Newcomb, 1906 What I’m Going to Talk About • • • • • • • The Sky Tonight Where did it all come from The Big Bang The life cycle of stars The source of a star’s power The death of stars The chemical elements from stars The Sky Tonight (20oct05) The Brightest Stars in Our Skies Common Name Sun Sirius Canopus Rigil Kentaurus Arcturus Vega Capella Scientific Name Sol Alpha CMa Alpha Car Alpha Cen Distance (light years) 1.5 x 10-5 8.6 74 4.3 Apparent Magnitude -26.72 -1.46 -0.72 -0.27 Absolute Magnitude 4.8 1.4 -2.5 4.4 Spectral Type G2V A1Vm A9II G2V + K1V Alpha Boo Alpha Lyr Alpha Aur 34 25 41 -0.04 0.03 0.08 0.2 0.6 0.4 Rigel Procyon Achernar Betelgeuse Hadar Acrux Beta Ori Alpha CMi Alpha Eri Alpha Ori Beta Cen Alpha Cru ~1400 11.4 69 ~1400 320 510 0.12 0.38 0.46 0.50 (var.) 0.61 (var.) 0.76 -8.1 2.6 -1.3 -7.2 -4.4 -4.6 Altair Aldebaran Antares Spica Pollux Fomalhaut Becrux Deneb Regulus Adhara Alpha Aql Alpha Tau Alpha Sco Alpha Vir Beta Gem Alpha PsA Beta Cru Alpha Cyg Alpha Leo Epsilon CMa Alpha Gem Gamma Cru Lambda Sco 16 60 ~520 220 40 22 460 1500 69 570 0.77 0.85 0.96 0.98 1.14 1.16 1.25 1.25 1.35 1.50 2.3 -0.3 -5.2 -3.2 0.7 2.0 -4.7 -7.2 -0.3 -4.8 K1.5IIIp A0Va G6III + G2III B81ae F5IV-V B3Vnp M2Iab B1III B0.5Iv + B1Vn A7Vn K5III M1.5Iab B1V K0IIIb A3Va B0.5III A2Ia B7Vn B2II 49 120 330 1.57 1.63 (var.) 1.63 (var.) 0.5 -1.2 -3.5 A1V + A2V M3.5III B1.5IV Castor Gacrux Shaula (var.) (var.) (var.) (var.) Interpreting the Table • Distance – In light years • Apparent Magnitude – Brightness as seen from Earth • Absolute Magnitude – Luminosity or brightness if ALL stars at 10pc • Spectral Type (example for Sun which is G2V) – G is spectral class – 2 is spectral sub-class • With spectral class leads to specific surface temperature – V is luminosity class • Giant (I, II III), sub-giant (IV) or main sequence (V) – Main sequence is defined as hydrogen core fusion Where Stars Came From: The Big Bang • The name “Big Bang” itself – Given by Fred Hoyle to mock the original theory formalized by George Gamow in a discussion on radio in the early 1950s • Common MISCONCEPTIONS – An explosion like any other – We can picture it from outside – It gave off a sound like an ordinary explosion What Came from the Big Bang • • • • • • • • • • • • • • (Higgs Fields?) (Strings?) Radiation Particles Electron / Positron Particle/Anti-particle Interactions Inflation Spontaneous Symmetry Breaking Cosmos / Universe Gravity Strong Force Quarks Proton Neutron Nuclear Fusion Alpha Radioactivity Beta Radioactivity Atoms Gases, liquids, solids Electric Charge Magnetism Cosmic Background Radiation Dark Matter Dark Energy Life You and me Physics of the Universe • Space, Time, Matter and Forces • Types of Matter – Quarks -> Baryons • protons, neutrons – Electrons -> Leptons • electrons, neutrinos, muons • Types of Forces – gravity, electromagnetism, strong, weak Measurements of Doppler Shift • A change in measured frequency caused by the motion of the observer or the source – classical example of pitch of train coming towards you and moving away Hubble’s Law Derived from Observations of Galaxies • The further away a galaxy is, the greater its recessional velocity and the greater its spectral red shift Concluding from Hubble’s Law • From Hubble’s Law we can calculate a time in the past when universe was a point – Simple but not all that easy • Big bang occurred about 14 billion years ago – big bang first proposed by Gamow based upon such evidence • Foretold of evidence of cosmic microwave background and distribution of chemical elements in universe The Vacuum Era • The Planck Epoch – <10-43 sec. and about 1019 GeV (1 GeV = ~1013K) – we just don’t know • The Inflationary Epoch – >10-43 sec., < 10-10 sec. – expansion driven by “repulsive gravity” The Radiation Era • • • • • • • Creation of light Creation of baryonic matter Electroweak epoch Strong epoch Decoupling of weak interaction Creation of nuclei of the light elements Decoupling of radiation spectrum The Matter Era • Transition from radiation domination to matter domination • Last scattering • Dark Ages • Galaxy Formation Epoch • Bright Ages The Degenerate Dark Era • Whither the future? – death of stars – black hole domination – black holes combine • What’s Next? – discussion held to another time Summary of the Universe’s Timescale Era The Vacuum Era Epochs Main Event Planck Epoch Quantum Inflationary Epoch fluctuation Inflation Time after bang <10-43 sec. <10-10 sec. The Radiation Era Electroweak Epoch Formation of Strong Epoch leptons, bosons, Decoupling hydrogen, helium and deuterium The Matter Era Galaxy Epoch Galaxy formation Stellar Epoch Stellar birth 10-10 sec. 10-4 sec. 1 sec. - 1 month The Degenerate Dark Era 20-100 billion yrs. 100 billion - ???? Dead Star Epoch Black Hole Epoch Death of stars Black holes engulf? 1-2 billion years 2-15 billion years The Evidence So Far • Evidence for a “Big Bang” – expansion of the universe • galaxies receding from us – everywhere the same (homogeneous and isotropic) – remnants of the energy from the “Big Bang” • a very hot body that has cooled – 2.7 K cosmic background radiation – the primordial abundance of chemical elements Cosmic Microwave Background • How hot would the cosmic background radiation be – close to 3 K • first noticed by Penzias and Wilson – Got Nobel Prize • interpreted by Dicke – Didn’t get Nobel Prize • confirmed by COBE satellite • again confirmed by WMAP Putting it into context • Taking the perspective of the universe with you at the center The CMB remainder • Using COBE DIRBE data for examining the fine differences – fine structure of the universe • led to the galaxies and their location To WMAP and Galaxies Types of Galaxies (established by Hubble) • Spiral • Barred Spiral • Elliptical • Irregular Understanding the aging of stars requires both observation and application of physical principles • Because stars shine by thermonuclear fusion of a fuel (hydrogen, etc.), they have a finite life span – they do not live forever • The theory of stellar evolution (bad name, really the life cycle of stars, or the development of stars) describes how stars form and change during their life span The Life Story of Stars • Gravity squeezes • Pressure forces resist – Kinetic pressure of hot gases – Repulsion from Pauli exclusion principle for electrons - white dwarf – Repulsion from Pauli exclusion principle for neutrons - neutron star – None equal to gravity - black hole • Energy loss decreases pressure • Energy generation replaces losses • Star is “dead” when energy generation stops – White dwarf, neutron star, black hole Luminosity Surface Gravity Weight of outer layers Gas Pressure Thermal Energy Center The Spectral Measure of Stars Wien’s and Stefan-Boltzmann’s Laws The HertzsprungRussell (HR) Diagram Interstellar gas and dust pervade the galaxy • Interstellar gas and dust, which make up the interstellar medium, are concentrated in the disk of the Galaxy • Clouds within the interstellar medium are called nebulae • Dark nebulae are so dense that they are opaque • They appear as dark blots against a background of distant stars • Emission nebulae, or H II regions, are glowing, ionized clouds of gas • Emission nebulae are powered by ultraviolet light that they absorb from nearby hot stars • Reflection nebulae are produced when starlight is reflected from dust grains in the interstellar medium, producing a characteristic bluish glow Interlude – Up in the Sky Tonight Protostars form in cold, dark nebulae • Star formation begins in dense, cold nebulae, where gravitational attraction causes a clump of material to condense into a protostar • As a protostar grows by the gravitational accretion of gases, KelvinHelmholtz contraction causes it to heat and begin glowing The more massive the protostar, the more rapidly it evolves Protostars evolve into main-sequence stars • A protostar’s relatively low temperature and high luminosity place it in the upper right region on an H-R diagram • Further evolution of a protostar causes it to move toward the main sequence on the H-R diagram • When its core temperatures become high enough to ignite steady hydrogen burning, it becomes a main sequence star Interlude - Humor • “OK stellar recruits, it’s time to learn what’s really in store for you! I know that before you signed up to be a massive star you read the fancy brochures that talked about how brightly you’d be shining and how you’d be visible from halfway across the galaxy. But you mo-rons must not have bothered to read the fine print that said that you’d explode in seven million years! And if you did read it then you’re even stupider than you look. Seven million is not a long time!” » Eric Schulman [A Briefer History of Time] Young star clusters give insight into star formation and evolution • Newborn stars may form an open or galactic cluster • Stars are held together in such a cluster by gravity • Occasionally a star moving more rapidly than average will escape, or leave the cluster • A stellar association is a group of newborn stars that are moving apart so rapidly that their gravitational attraction for one another cannot pull them into orbit about one another • Star-forming regions appear when a giant molecular cloud is compressed • This can be caused by the cloud’s passage through one of the spiral arms of our galaxy, by a supernova explosion, or by other mechanisms Supernovae compress the interstellar medium and can trigger star birth A star’s lifetime on the main sequence is proportional to its mass divided by its luminosity • The duration of a star’s main sequence lifetime depends on the amount of hydrogen in the star’s core and the rate at which the hydrogen is consumed • The more massive a star, the shorter is its mainsequence lifetime The Sun has been a main-sequence star for about 4.56 billion years and should remain one for about another 7 billion years During a star’s main-sequence lifetime, the star expands somewhat and undergoes a modest increase in luminosity When core hydrogen fusion ceases, a mainsequence star becomes a red giant Red Giants • Core hydrogen fusion ceases when the hydrogen has been exhausted in the core of a main-sequence star • This leaves a core of nearly pure helium surrounded by a shell through which hydrogen fusion works its way outward in the star • The core shrinks and becomes hotter, while the star’s outer layers expand and cool • The result is a red giant star Fusion of helium into carbon and oxygen begins at the center of a red giant • When the central temperature of a red giant reaches about 100 million K, helium fusion begins in the core • This process, also called the triple alpha process, converts helium to carbon and oxygen • H-R diagrams and observations of star clusters reveal how red giants develop • The age of a star cluster can be estimated by plotting its stars on an H-R diagram As a cluster ages, the main sequence erodes away from the upper left as stars of progressively smaller mass evolve into red giants Planetary Nebulae – Death of a Solar Mass Star Planetary Nebula - NGC 7293 450 light years away in Aquarius Planetary Nebula - NGC 7027 3000 light years away in Cygnus Aging from Giants to Dwarfs White Dwarf Properties Sirius A Sirius B - WD Property Earth Sirius B Su n Mass (Msun) 3x10 -6 0 .9 4 1 .0 0 0 .0 0 9 0 .0 0 8 1 .0 0 Luminosity (Lsun) 0 .0 0.0028 1 .0 0 Surface temperature (K) 287 27,000 5770 6 1 .4 1 Radius (Rsun) 3 Mean density (g/cm ) Central temp (K) 3 Central density (g/cm ) 5 .5 2.8x10 4200 2.2x10 9 .6 3.3x10 7 7 7 1.6x10 160 Life Cycle by Mass from the Main Sequence Main sequence stars Supergiants Giants Helium flash C detonation Heavy nuclei fusion Supernovae Planetary nebulae Black holes Ns White dwarfs 100 40 10 4.0 Mass (MSun = 1) 1.0 0.4 0.1 A Massive Star (~25 Msun) SN 1987A Outburst Large Magellanic Cloud February 23, 1987 Progenitor star was a blue supergiant of about 20 Msun Crab Nebula - 1054 A.D. Neutron star Copyright © Periodic Table of the Elements, Los Alamos National Laboratories © Periodic Table of the Elements Los Alamos National Laboratories There are 92 elements produced naturally. Aside from hydrogen, helium and a little lithium, they were all produced BY THE STARS. References (Books) • Hogan, Craig (1997). The Little Book of the Big Bang, Copernicus Springer-Verlag. • Adams, Fred and Greg Laughlin (1999). The Five Ages of the Universe, The Free Press. • Schulman, Eric (1999). A Briefer History of Time, W.H. Freeman and Company. • Chaisson, E. and S. McMillan (1999). Astronomy Today, Prentice Hall. • Freedman, R.A. and Kaufmann, W.J. (2004). Universe, 7th edition, W.H. Freeman and Company. • Seeds, M. (1998). Horizons, Exploring the Universe, Fifth Edition, Wadsworth Publishing Co. References (World Wide Web) • Web pages for general information and other links – http://physics.gmu.edu/~hgeller/ • http://antwrp.gsfc.nasa.gov/apod/astropix.html – astronomy picture of the day • http://itss.raytheon.com/cafe/cafe.html – the astronomy café (reference and questions) • http://physics.gmu.edu/~jevans/astr103/astr103.html – Introductory astronomy with John Evans • http://physics.gmu.edu/~jevans/astr328/astr328.html – Introductory astrophysics with John Evans • http://genesismission.jpl.nasa.gov/ – NASA Genesis Mission • H-R Diagram Software – http://www.cvc.org/astronomy/freeware.htm • Stellar Evolution Software – http://leo.astronomy.cz/sclock/sclock.html Acknowledgements • Thanks to my colleagues in the Department of Physics and Astronomy including Maria Dworzecka, Bob Ehrlich, Bob Ellsworth, John Evans, Menas Kafatos, Jean Mielczarek, Rita Sambruna, Indu Satija, Shobita Satayapal, Mike Summers, John Wallin, Joe Weingartner. • Also thanks to W.H. Freeman Company, Prentice-Hall, American Institute of Physics History Center, NASA Genesis Mission EPO, NASA JPL, NASA STScI, and NASA GSFC.