brlsijune2004

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Published on November 29, 2007

Author: Cannes

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Cosmic Fireworks: X-Rays From Black Holes:  Cosmic Fireworks: X-Rays From Black Holes Daniel Evans Contents:  Contents My background What is a black hole? Telescopes What is an active galaxy? Do active galaxies harbour black holes? Case study: Centaurus A What can black holes tell us about the Universe as a whole? My Background:  My Background M.Sci. Physics, Grey College, University of Durham Supervisor Professor Sir Arnold Wolfendale, F.R.S., 14th Astronomer Royal My Background:  My Background Ph.D. Astrophysics University of Bristol Harvard-Smithsonian Center for Astrophysics What is a black hole?:  What is a black hole? “Nothing travels faster than light” What is a black hole?:  What is a black hole? Concept All objects with mass have gravity (e.g. the Earth) “Jump” with sufficient speed  escape Earth’s gravity (think space shuttles) Einstein: nothing is faster than light What is a black hole?:  What is a black hole? What is a black hole?:  What is a black hole? How heavy? From a few x the mass of the sun up to 1 billion x the mass of the sun (See later!) How big? Fairly simple (GCSE/A Level) physics! For 3 x the mass of the sun, event horizon = 3 km For 1 billion x the mass of the sun, event horizon = 1 AU (Earth-Sun distance) What is a black hole?:  What is a black hole? EH X-Ray Telescopes:  X-Ray Telescopes XMM-Newton (ESA) Launched in 1999 3.8 tonnes Largest satellite built in Europe Very large collecting area Good resolution X-Ray Telescopes:  X-Ray Telescopes X-Ray Telescopes:  X-Ray Telescopes Chandra (NASA/SAO) Launched in 1999 on STS-93 (Columbia) 25 tonnes Largest object ever carried by shuttle Exceptionally high resolution X-Ray Telescopes:  X-Ray Telescopes X-Ray Telescopes:  X-Ray Telescopes “First Light”: SNR Cas A What is an Active Galaxy?:  What is an Active Galaxy? Take a “normal” galaxy: The “Sombrero” galaxy The total energy is the sum of all the energy from the stars What is an Active Galaxy?:  What is an Active Galaxy? This is not the case in an active galaxy There are very bright core and jet components This is not starlight! In some cases (e.g. quasars) the non-stellar emission completely dominates What is an Active Galaxy?:  What is an Active Galaxy? Something very heavy is lurking at the centre… Evidence: 1. Very bright central core, often a jet Chandra X- ray image of NGC 6251 Core Jet Power = 1 billion billion billion billion Watts E=mc2  highly efficient What is an Active Galaxy?:  What is an Active Galaxy? 2. Orbital speeds Again, using fairly simple physics, we can use the velocities of orbiting objects to estimate the mass of the central core What is an Active Galaxy?:  What is an Active Galaxy? 3. (A bit more technical): Relativistic broadening of X-ray emission lines (Einstein again): Something is orbiting very fast around something very heavy What is an Active Galaxy?:  What is an Active Galaxy? The central object is also small A B What is an Active Galaxy?:  What is an Active Galaxy? The central object is also small A B What is an Active Galaxy?:  What is an Active Galaxy? The central object is also small A B What is an Active Galaxy?:  What is an Active Galaxy? The central object is also small A B What is an Active Galaxy?:  What is an Active Galaxy? The central object is also small A B What is an Active Galaxy?:  What is an Active Galaxy? The central object is also small A B d = ct c = speed of light d = diameter The ‘red’ light reaches us over a period t, say 1 ms Do Active Galaxies Harbour Black Holes?:  Do Active Galaxies Harbour Black Holes? Candidates for the “heavy central object”: 1. A supermassive star Non-rotating star unstable on a timescale of approx 10 million years (too low – Universe is around 15 billion years old) Can be stabilised by rotation, but general relativity predicts additional instability and star evolves into black hole Do Active Galaxies Harbour Black Holes?:  Do Active Galaxies Harbour Black Holes? 2. A “starburst” nucleus A dense cluster of massive, rapidly evolving stars lies in the nucleus, undergoing many supernova explosions Radio observations demonstrate well-ordered motions (ie jets!) which are hard to explain in a model involving random outbursts Do Active Galaxies Harbour Black Holes?:  Do Active Galaxies Harbour Black Holes? 3. A black hole! Centaurus A:  Centaurus A Closest active galaxy (11 million light years) Complex structure on all scales Studied across the electromagnetic spectrum Multiwavelength Centaurus A:  Multiwavelength Centaurus A Optical and IR Elliptical galaxy crossed by dust lane Evidence for a recent merger Recession velocity = 540 km/s, z=0.0018 HST: 130 light year diameter disk. Material fed into inner accretion disk Slide31:  Blanca 4m telescope image Multiwavelength Centaurus A:  Multiwavelength Centaurus A Radio overview 8o x 4o extended, diffuse emission Inner radio lobes NE and SW of the centre Predominantly one-sided jet NE of the centre Inner jet and nucleus Tingay et al. (1998) Multiwavelength Centaurus A:  Multiwavelength Centaurus A Haslam 408 MHz radio all-sky map Multiwavelength Centaurus A:  Multiwavelength Centaurus A Radio: VLA Synchrotron radiation Slide37:  Radio X-ray (Hardcastle et al. 2003) Multiwavelength Centaurus A:  Multiwavelength Centaurus A X-ray: Brightest extragalactic object in the hard X-ray sky Ideal object to study Much-studied by earlier X-ray missions Slide39:  Thermal gas Jet Point Sources SW Radio Lobe Nucleus 31 knots Synchrotron radiation 246 detected “X-ray binaries” X-ray emitting plasma surrounding lobe Supersonic expansion Elliptical galaxy Incredibly luminous Centaurus A - Spectrum:  Centaurus A - Spectrum Now we turn to spectral analysis Spectra can tell us the elements and physical processes present in the black hole system Centaurus A - Spectrum:  Centaurus A - Spectrum Centaurus A - Spectrum:  Centaurus A - Spectrum Centaurus A - Results:  What can I tell from this? There is a dense and incredibly luminous core A powerful jet extends into the intergalactic medium (space) There is an elliptical host galaxy underneath Centaurus A - Results Centaurus A - Conclusions:  Major conclusions Strong evidence for a supermassive black hole in the centre of Cen A Energy generation mechanisms classified A picture emerges… Centaurus A - Conclusions Let’s Take This To Higher Distances:  Let’s Take This To Higher Distances AGN are bright They can be seen out to very large distances (14 billion light years) They can be used to probe cosmological models Let’s Take This To Higher Distances:  Let’s Take This To Higher Distances The 2QZ survey: Used to measure the position on the sky, and redshift (~distance) of quasars (a type of active galaxy) Theory Experiment Results Of Survey:  Results Of Survey Up until about 10-15 years ago, we thought that the Universe was composed entirely of matter. This turned out to be wrong… Amazingly, we know for sure just 3% of the energy density This is ordinary matter (baryonic)  27% is dark matter  70% is dark energy/ quintessence/ cosmological constant Summary:  Summary Very strong evidence that supermassive black holes exist at the heart of all AGN They have a mass ~ 100 million x the mass of the sun AGN often form jets AGN tell us that the energy content of the Universe is dominated by “dark energy”

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