Final Exam Review Prof. Tom Megeath. We are now in the greatest age of astronomical discovery. Basics

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1 Final Exam Review A2020 Prof. Tom Megeath We are now in the greatest age of astronomical discovery The oldest detected object: GRB A gamma ray burst which occurred 630 million years after the big bang. This may be death of one of the first stars.. Basics Know the sizes of things (to an order of magnitude) 1

2 Overview: Physics Classic Physics: Newton s laws Law of Universal Gravitation Light (electromagnetic spectrum, blackbody radiation, synchrotron, bremstrahlung, emission line from atoms, 21 cm from atomic Hydrogen, emission from molecules (CO), Kirchoff s laws) Modern Physics: Special Relativity (inertial rest frames, time dilation, length contraction, simultaneity, mass (E=mc 2 ) General Relativity (mass causes spacetime to curve, curvature of spacetime tells mass where to go) Quantum mechanics (uncertainty principles) Basic Properties of Stars Spectral types (OBAFGKM) and temperatures (what spectral type is our sun?) Stars are approximately blackbodies The main sequence and the stellar thermostat. Dependence of stellar properties with mass for main sequence stars. Nuclear fusion (proton chain and CNO cycle) Stars vs brown dwarfs How does energy travel from core of star to surface. What spectral types are most common in the solar neighborhood? Clusters of stars: open (galactic clusters) and globular clusters KNOW THE HR DIAGRAM Star Formation Molecular cloud - competition between thermal pressure and gravity Protostar - star growing in mass, energy generated by gas falling onto star, disk forms due to conservation of angular momentum Pre-main sequence phase - star forms to large, must slowly contract before nuclear fusion. Contraction time depends on mass with a one solar mass star contracting in 50 Myr Disks - pre-main sequence stars form with disks - disks are the primordial material of planets, disks disappear in a few million years. Many (60%) of stars form in clusters - like the cluster in the Orion nebula Stellar Evolution: Low mass stars: depletion of Hydrogen in core leads to shell burning helium ash makes core denser leading to more shell burning Helium fusion occurs at Helium flash, leads to Helium star Helium converted to carbon, two shell burning Flashes - Planetary Nebula with white dwarf Massive stars: multiple shell burning carbon fuses into heavier elements continues upward until Iron Iron core collapses (in a few seconds) from size of sun to a few kilometer neutron star - this powers supernova 2

3 The Cosmic Graveyard White dwarfs: created by low to intermediate mass stars supported by electron degeneracy pressure have masses less than Chandrasekhar mass (1.4 msun) initially hot, but cool with time incredible dense (mass of sun, size of Earth) binaries can result in novae and white dwarf supernovae Neutron stars created by high mass stars size of city, more massive than sun have masses less than Chandrasekhar mass (3 msun) create pulsars (rotating too fast for normal star) binaries with normal star lead to X-ray binaries Black holes created by high mass stars, colliding neutron stars, accreting neutron stars at event horizon, escape velocity equals speed of light time slows down near even horizon candidates in our galaxy: X-ray binary Cygnus X-1, center of our galaxy The Interstellar Medium Main constituents: Atomic Hydrogen (and mixture of other atoms primarily He) Dust: (micron sizes dust grains - 1/100 the mass of gas) Ionized gas: near hot stars UV creates ionized hydrogen, HII regions Molecular gas: in dense regions - dust shields gas and hydrogen and other atoms which the form molecules (such as CO) Structures: Molecular clouds HII regions Planetary Nebula Supernova remnants Superbubbles Galactic fountains Recycling: gas forms stars, stars enrich gas with heavier elements stars release part of gas in supernova and planetary nebula, gas is swept up into superbubbles by winds and supernova some of this gas may be dense enough to form molecular clouds Galaxies Hubble s tuning fork Spiral, barred spirals, irregular, elliptical Structure of spiral galaxies (bulge, (bar), disk, spiral arms, halo, globular clusters) Why spiral arms look blue and ellipticals look red. Starburst Galaxies AGN and Quasars Formation of galaxies Formation of ellipticals Dark matter in galaxies (rotation curves) Interacting Galaxies Galaxy clusters Measuring Distances Parallax - only works for nearby stars Clusters - main sequence fitting - only works in our galaxy Standard candles cepheids (period luminosity relationship) tully-fisher relationship (lumonsity of galaxy vs rotation velocity) white dwarf supernovae (can be seen at greatest distances) For distant galaxies, can measure doppler shift and use Hubble s law 3

4 Isotropy Cosmology Hubble s law and expanding universe Dark matter, voids and superclusters (VOIDS ARE NOT FILLED WITH DARK MATTER - THE DARK MATTER IS CONCENTRATED IN SUPERCLUSTERS AND FILAMENTS) Critical density and the fate of the universe Curvature of Universe vs critical density Dark energy and the accelerating universe Cosmic Evolution in a Nutshell Big bang (13.7 billion years ago measured from Hubble flow) Inflation (inferred) Antimatter annihilated (1 out of every billion proton survives - inferred) Nucleosynthesis produces Helium, Deuterium, some Lithium an Beryllium (3 minutes after big bang- we see product in abundance of Helium and other elements) Atoms form - cosmic microwave background (380,000 years after big bang- detected by radio telescopes) First stars and galaxies form (by 1 billion years - we are still searching for these) Star continue to form and create heavier elements (we see this process in action as we look out to greater and greater distances - evidence also found in our own Galaxy) Our solar system forms (4.7 billion years ago measured from radioactive isotopes) Star formation, star death, cosmic recycling continues, new planets form, life? The Fate of the Universe Primordial Era n < 6 Stelliferous Era n = 6-14 Degenerate Era n = Black Hole Era n = Dark Era n > 100 Time = 10 n years Life in the Universe SETI - search for extraterrestrial intelligence Optical and Radio SETI Leakage and Deliberate Signals The Drake Equation Detection of Disks and Exoplanets Exogenic, Endogenic and Panspermia Tree of life and evolution Habitable zones Oxygen and finding planets with life Interstellar travel and the twin paradox 4

5 Final Exam MH 2002 (this room) Thursday at 10:15 to 12:15!!! Please contact me by to schedule office hours during finals. I will be at the National Science Foundation (Arlington VA) doing my service to the astronomical community 5