Introduction to Astrophysics. Professor David Cinabro

Transcription

1 Introduction to Astrophysics Professor David Cinabro

2 Disclaimer Subject is vast Covers everything from Physics of the Atmosphere to the Origin and Fate of the Universe and everything in between Impossible to introduce all of it in ~1 hour Focus on research we do here Professor Cackett - Accretion Professor Cinabro - Cosmology with SN 2

3 ACCRETION POWER IN ASTROPHYSICS Professor Cackett ac cre tion \a- krē-shən\: noun the process of growth or enlargement typically by the gradual accumulation of additional layers or matter

4 Credit: Hubble Space Telescope Jet ACCRETION Disk of gas Accretion: process by which an object gains/accumulates mass Extremely important process throughout the Universe from young stars to supermassive black holes at the centers of galaxies A young star forming and accreting matter from a disk Artist s impression of accretion onto a black hole

5 A SOURCE OF ENERGY Extraction of gravitational potential energy as material accretes onto a massive object Accretion disk gravitational potential energy converted to radiation through friction Due to conservation of angular momentum, accreting material usually forms a rotating thin disk Accretion in binary system

6 MORE EFFICIENT THAN FUSION! Nuclear fusion, which powers stars, is less than 1% efficient for H He: Enuc = mc 2 Energy from accretion is given by: Eacc = GMm/R Nuclear fusion powers stars like the Sun For compact objects (neutron star or black hole) accretion is greater than 20 times more efficient than fusion!

7 MAXIMUM ACCRETION RATE As Eacc = GMm/R the more massive an object and the smaller it is, the greater the energy released through accretion But, there is a limit to how much energy is radiated away, the Eddington Limit: inward gravitational force on matter must be greater than the outward radiation pressure otherwise it would blow itself apart Einstein & Eddington at the University of Cambridge

8 COMPACT OBJECTS Accretion most powerful onto compact objects Black hole: a massive object whose gravitational force is so strong that not even light can escape Light near a black hole gets bent by the strong gravity there Neutron star: a star about 1.5 times the mass of the Sun, but with a radius of only ~10 km - a star the size of a city!

9 BLACK HOLES Come in several flavors : stellar-mass black holes (~10 Msun) formed in supernovae supermassive black holes ( Msun) found at the centers of galaxies Stars orbiting around the black hole at the center of the Milky Way

10 QUASARS aka Active Galactic Nuclei Light from the central region outshines the entire galaxy! Only way to power is by accretion of gas onto a black hole The M87 Jet Light from accretion disk Using the Eddington Limit can estimate that black holes at the centers of galaxies must be typically between Msun PRC00-20 Space Telescope Science Institute NASA and The Hubble Heritage Team (STScI/AURA) A nearby Active Galactic Nucleus shoots a highspeed jet of gas

11 STELLAR-MASS BLACK HOLES Can be formed in a supernova explosion at the end of a massive star s life Often found in binary systems Black hole can accrete matter from the companion star! Matter can be pulled from the companion star to the black hole

12 NEUTRON STARS Also can be formed in supernovae About 1.5 Msun in 10 km radius average density > than atomic nuclei Crust: nuclei, n, e Outer Core:n,p,e Inner Core:? densest observable matter in Universe made mostly of neutrons, but may contain exotic matter at the center Where? could be: hyperon condensate, kaon condensate, strange quark matter...

13 NEUTRON STARS Like stellar-mass black holes, can often be found in binary systems Can also accrete matter from the companion star Accretion onto a neutron star

14 OBSERVING ACCRETION ONTO COMPACT OBJECTS Gas accreting onto black holes and neutron stars gets extremely hot (millions of degrees) The gas therefore emits thermally in X-rays From MAXI onboard the ISS An all-sky X-ray image: the brightest X-ray sources in the sky come from accretion onto black holes and neutron stars

15 X-RAY TELESCOPES X-rays do not penetrate the Earth s atmosphere, so have to go into space CHANDRA X-rays will pass through conventional optical telescope mirrors, so have to focus X-rays with special grazing-incidence mirrors XMM-NEWTON Major NASA and ESA missions are : Chandra and XMM-Newton

16 THE CHANDRA MIRRORS OBSERVING X-RAYS

17 ACCRETION SUMMARY Accretion onto compacts objects is the ultimate power source in the Universe Prof. Cackett works on X-ray observations of accretion onto black holes and neutron stars to try and understand these objects

18 Cosmology with supernovae David Cinabro

19 Cosmology Background The study of the origin and evolution of the Universe. Last 20 years have been a golden age in which we have learned: Origin is a giant explosion known as the Big Bang Fate is most likely continued expansion Most of the Universe is in the Dark Sector: Dark Matter: Unknown sort that dominates over ordinary matter Dark Energy: Unknown force that is pushing the Universe apart

20 Discovery of the Expanding Universe: Hubble 1929 Measured distances to 25 galaxies: Used cepheids for Andromeda and Local Group Used brightest stars in the others Compared distances with recession velocities. Finds that the velocity gets larger with distance, the Hubble Law, and slope is the Hubble parameter, H

21 Echo of the Explosion: Gamow (1948) Gamow and Alpher consider the consequences of an expanding Universe. First conclusion is that the Universe should be filled with E+M radiahon lei over from when it was small and hot. Today should be Microwaves (Blackbody with T = 3K).

22 Cosmic Microwaves (1963) Serendipitously observed at Bell Labs using a communicahons instrument. Death blow to alternate Steady State cosmology of Fred Hoyle.

23 Astronomer s Periodic Table Gamow, Alpher, Herman add in Nuclear Physics to calculate the abundances of the elements arising from the hot, dense early Universe ( ). Agrees with observahons that grow increasingly precise.

24 Triumph of the Big Bang Ironically the term was coined derisively by Fred Hoyle, supporter of Steady State, in a 1949 radio broadcast. Three pillars: 1) Expanding Universe 2) Cosmic Microwave Background 3) Cosmic Elemental Abundances Only serious Cosmology by the mid s Unfortunately it leaves only two alternahves for the fate of the Universe

25 Big Bang starts the expansion of the universe. But there is enough mass in the universe that gravity captures all the galaxies, the universe begins to contract, making gravity stronger, accelerates contrachon, and eventually the universe is compressed into a single point(?). We call this

26 Big Bang starts the expansion of the universe. But there is enough mass in the universe that gravity captures all the galaxies, the universe begins to contract, making gravity stronger, accelerates contrachon, and eventually the universe is compressed into a single point(?). We call this The Big Crunch

27 Big Bang starts the expansion of the universe. But there is not enough mass in the universe for gravity to capture the galaxies, and the universe expands, at an ever slowing rate, forever. Stars begin to run out of fuel and burn out, and since the universe gets less and less dense no new stars form. It gets colder and colder unhl the universe freezes to death. We call this

28 Big Bang starts the expansion of the universe. But there is not enough mass in the universe for gravity to capture the galaxies, and the universe expands, at an ever slowing rate, forever. Stars begin to run out of fuel and burn out, and since the universe gets less and less dense no new stars form. It gets colder and colder unhl the universe freezes to death. We call this The Big Chill

29 Cosmic Microwave Background Snap shot of matter density of the universe at the photon surface of last scattering. Most accurate from Planck satellite.

30 M51: June 2005 M51: July 2005

31 Describing the Universe How Astronomers describe the Universe on the cosmological scale. Repulsive cosmological constant(λ) versus agrachve mass(m). 1.0 = Enough agrachve to force Big Crunch. 1.0 Ω Λ 0.0 No Big Bang Big Chill Ω 1.0 m Big Crunch

32 Concordance Model Cosmology Another three pillars 1) CMB map 2) SNIa vs redshii 3) Galaxy clustering Dark Energy is most like a strong version of Einstein s Cosmological Constant

33 Cosmologies Golden Age The Universe is mostly stuff about which we are IGNORANT. Countless explanahons, but none are very sahsfying and as yet no experiment or observahon are decisive on the nature of the Dark Sector.

34 Sloan Digital Sky Survey Supernova Search World s sample of supernovae is quite small (~1000) More would allow tests of Dark Energy (Is it constant in time? Is it constant in space?) Sloan Digital Sky Survey ideal for this work (

35 Supernova Candidate

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38 Core Collapse SN Rate 38

39 Galaxy Host Properties 39

40 CCD R&D at LBNL 40

41 REU Student Opportunities Vast Continued analysis of SDSS-SN data set... Opportunities at FNAL. MS-DESI: Take astro spectra like SDSS took images. CCD R&D work at LBNL. LSST: Monster scale up of SDSS. Workers needed for simulation and hardware. Opportunities at SLAC. Development of SN Software Analysis package SNANA. Work with WSU Comp Sci.

42 Astrophysics Summary Plenty of work to do. Last 3 years 10 projects. Zachary Elledge (Neutron Star State vs Accretion Disk Inner Radius), Hansoul Lee (Focus, Guide and Alignment system for DESI at SLAC), Dustin Scriven (Automated Solar Observatory at Lake St. Clair Metropark) Joe Duszynski (Anomalous SNIa Light Curves), Renee Ludlam (Supermassive Black Holes in Dwarf Galaxies), Jim Snitzer (Quality of SN Image Subtraction, at FNAL), Ashley Walsh (Nuetron Star Variability) Rachael Merritt (SN Host vs Field Galaxies), Aron Zell (Accretion in NS), Meridith Joyce (Resolution of DES Camera at FNAL)