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FRONTIERS OF ASTROPHYSICS - giant telescopes, space missions and invisible wavelengths Michael Rowan-Robinson Imperial College London Nov 22nd 2008 Institute of Physics, Liverpool some frontier topics in astrophysics • Black holes • The dusty universe - dramatic starbursts in colliding galaxies • Exoplanets - the search for extraterrestial earths • Cosmology - measuring the size and age of universe with 5% precision - a universe of dark matter, dark energy Nov 22nd 2008 Institute of Physics, Liverpool first detection of electromagnetic radiation outside the optical band: Herschel (1800) detected infrared radiation from the sun Atmospheric transmission Nov 22nd 2008 Institute of Physics, Liverpool X-ray astronomy The first X-ray satellite, Uhuru (1970) detected X-rays from compact sources in binary systems (white dwarfs, neutron stars, black holes), from quasars (massive black holes) and from very hot gas in clusters of galaxies (100 million degrees) Nov 22nd 2008 Institute of Physics, Liverpool HOW TO OBSERVE BLACK HOLES? • Black holes give off no light from within the event horizon • Must observe effects on environment near horizon, in particular: – VELOCITIES (matter speeds up near hole) – ACCRETION (matter being sucked into hole and heated to X-ray temperatures) – REDSHIFT (time slows down near hole) * Effect of Einstein’s General relativity * Nov 22nd 2008 Institute of Physics, Liverpool Cygnus X-1, a 10 solar mass black hole in our Galaxy Nov 22nd 2008 Institute of Physics, Liverpool X-ray spectra of black holes in Active Galactic nuclei • Hypothesis: The nucleus of an Active Galaxy contains a black hole being fed by an accretion disk. X-rays illuminate the disk inducing emission from iron. • Prediction: shape of line distorted by huge velocities and gravitational shifts Nov 22nd 2008 Institute of Physics, Liverpool X-rays WE SEE THESE EFFECTS! • X-ray iron spectrum from the ASCA satellite • Clear broadening and ASCA redshift • Requires black hole Line profile depends on: • Inclination • Inner radius • Outer radius • X-ray illumination pattern Tanaka et al. (1995) Nov 22nd 2008 Institute of Physics, Liverpool Nov 22nd 2008 Institute of Physics, Liverpool Nov 22nd 2008 Institute of Physics, Liverpool AND THEY ARE COMMON Nandra et al. (2007) New spectra from XMM-Newton Nov 22nd 2008 Institute of Physics, Liverpool the dusty universe IRAS 1983 - SPITZER, 2003 Nov 22nd 2008 Institute of Physics, Liverpool IRAS - star forming regions LMC, the Large Magellanic Cloud Nov 22nd 2008 Institute of Physics, Liverpool constellation Orion Uultraluminous infrared galaxies IRAS discovered ultraluminous infrared galaxies, forming stars 100-1000 times faster than our Galaxy, probably caused by mergers between two galaxies this is an image of Arp 220 Nov 22nd 2008 Institute of Physics, Liverpool Sombrero galaxy - end product of a galaxy merger Nov 22nd 2008 Institute of Physics, Liverpool IC1396, the Elephant’s Trunk - a dark globule inside an emission nebula - a pair of newly formed stars have created a cavity - the animation shows how the appearance changes from the optical, where dust absorbs light to the infrared where the dust radiates Nov 22nd 2008 Institute of Physics, Liverpool QuickTime™ and a MPEG-4 Video decompressor are needed to see this picture. Nov 22nd 2008 Institute of Physics, Liverpool IRAS - dust debris disks IRAS also discovered dust debris disks around stars, confirmed by imaging with the Hubble Space Telescope, evidence for planetary systems in formation. Today over 200 exoplanets are known. Nov 22nd 2008 Institute of Physics, Liverpool last week: HST image of exoplanet in Fomalhaut debris disk Nov 22nd 2008 Institute of Physics, Liverpool The Exo-Planet Discovery Era • <1995 • 1995 Solar System planets first extra-solar planet ( 51 Peg ) - Hot Jupiters! • 2008 ~300 exo-planets known • 2005-10 first Hot and Cool exo-Earths • 2010-15 Habitable Earths -- common or rare? • 2020-30 Extra-solar Life? Are we alone? Nov 22nd 2008 Institute of Physics, Liverpool Exoplanet Discovery Methods • Doppler Star Wobbles: ~230 • Transits: 39 • Microlensing: 7 Nov 22nd 2008 Institute of Physics, Liverpool 1995 First Doppler Wobble Planet: 51 Peg Discovered by accident: Mayor & Queloz (1995) Quickly confirmed: Marcy & Butler (1995) P = 4.2 days (!) a = 0.05 AU T ~2000K m sin(i) = 0.5 mJ New class of planet: “Hot Jupiters” (how did these form ?) Nov 22nd 2008 Institute of Physics, Liverpool Nov 22nd 2008 Institute of Physics, Liverpool WASP’s first 2 new Hot Jupiters UK WASP Consortium: Belfast, St.Andrews, Keele, Open, Leicester, Cambridge, IAC, SAAO Nov 22nd 2008 Institute of Physics, Liverpool Planetary, Brown-dwarf and substellar M-R relation 100 Log [ R / R_Jup ] 10 brown dwarfs, gas giants and rocky planets Low-Mass Stars RV discoveries WASP Gas Giant Planets HAT TrES XO OGLE Baraffe2003, 5 Gyr 1 Baraffe1998, 5 Gyr Fortney2007 1Gyr core00 a0.02 Fortney2007 4.5Gyr core10 a0.045 0.1 Fortney2007 Pure Ice Rock/Ice Planets Fortney2007 Pure Rock Solar-system planets Fortney2007 Pure Iron 0.01 0.00001 0.0001 0.001 Nov 22nd 2008 0.01 0.1 1 Institute Log [ M/ M_Jup ] 10 100 1000 of Physics, Liverpool 10000 How to find Earths ? • Hot Earths: Transits from Space – 2007-10 … CoRoT -- Launched 27 Dec 2006. – 2009-15 … Kepler – 2017 … PLATO • Habitable Earths: Hard to Find – Habitable Zone: T~300K liquid water on rocky planet surface • Cool Earths: Gravitational Lensing Nov 22nd 2008 Institute of Physics, Liverpool – 2004-14 … OGLE, PLANET/RoboNet, microFUN, MOA CoRoT (CNES) First CoRoT planet: 3 May 2007 Launch 27 Dec 2006 CoRoT-Exo-1b: 6 months/field P = 1.5 d ~ 103 t /min 1/ 2 Nov 22nd 2008 Institute of Physics, Liverpool m sin(i) = 1.3 mJ Space Transit Planet Catch Planet Size (rE) A few Earth-like Planets may be found. Nov 22nd 2008 habitable hot Jupiters Too large? Earths Too small? Too hot? of Physics, Liverpool PlanetInstitute Temperature (K) OB-03-235 / MB-03-053 2003 first microlens planet m ~ 1.3 mJ a ~ 3 AU MOA OGLE Bond et al. Nov 22nd 2008 (2004) OGLE alert Institute of Physics, Liverpool Aug 2005 OB-05-390 OB-05-390 smallest cool planet m ~ 6 m a ~ 2.9 AU PLANET/R oboNet OGLE MOA Nov 22nd 2008 Institute of Physics, Liverpool ESA: Darwin ~ 2020-30? infrared space interferometer destructive interference cancels out the starlight snapshot ~500 nearby systems study ~ 50 in detail Nov 22nd 2008 Institute of Physics, Liverpool Life’s Signature: disequilibrium atmosphere (e.g. oxygen-rich) simulated Darwin spectrum Which planet is alive? Nov 22nd 2008 Institute of Physics, Liverpool The distances of the galaxies In 1924 Edwin Hubble used Cepheid variable stars to estimate the distance of the Andromeda Nebula. It clearly lay far outside the Milky Way System. This opened up the idea of a universe of galaxies. Nov 22nd 2008 Institute of Physics, Liverpool The expansion of the universe Five years later he announced, based on distances to 18 galaxies, that the more distant a galaxy, the faster it is moving away from us velocity/distance = constant, Ho (the Hubble law) This is just what would be expected in an expanding universe. The Russian mathematician Alexander Friedmann had shown that expanding universe models are what would be expected according to Einstein’s General Theory of Relativity, if the universe is homogeneous (everyone sees the same picture) and isotropic (the same in every direction). Nov 22nd 2008 Institute of Physics, Liverpool The Hubble Space Telescope Key Program Following the first HST servicing mission, which fixed the telescope aberration, a large amount of HST observing time was dedicated to measuring Cepheids in distant galaxies, to try to measure the Hubble constant accurately. Nov 22nd 2008 Institute of Physics, Liverpool The HST Key program final result Ho = 72 km/s/Mpc uncertainty 10% (Freedman et al 2001) log V Nov 22nd 2008 Institute of Physics, Liverpool Implications of the Hubble constant Ho is (velocity/distance) so has the dimensions of (1/time). 1/Ho is the expansion age of the universe (how old the Universe would be if no forces acting) = 13.6 billion yrs For simplest model universe with only gravity acting, age of universe would be 9.1 billion years (gravity slows expansion) Nov 22nd 2008 Institute of Physics, Liverpool The age of the universe We can use the colours and brightnesses of the stars in globular clusters to estimate the age of our Galaxy ~ 12 billion years Long-lived radioactive isotopes give a similar answer Allowing time for our Galaxy to form, the age of the universe is ~ 13 billion years Nov 22nd 2008 Institute of Physics, Liverpool The age of the universe problem • This is a problem for the simplest models, where gravity slows down the expansion • To get consistency between the HST Key Program value of Ho and the observed age of the universe, we need to reverse the deceleration of the universe • Something is pushing the galaxies apart Nov 22nd 2008 Institute of Physics, Liverpool The discovery of the Cosmic Microwave Background, 1965 The discovery of the Cosmic Microwave Background (CMB) by Penzias and Wilson in 1965, and the confirmation of its blackbody spectrum by COBE in 1991, showed that we live in a hot Big Bang universe, dominated by radiation in its early stages. Nov 22nd 2008 Institute of Physics, Liverpool How much matter is there in the universe ? The light elements D, He, Li are generated from nuclear reactions about 1 minute after the Big Bang. The abundances turn out to depend sensitively on the density of ordinary matter in the universe. density ~ 4.10-28 kg/cu m Wb ~ 0.04 Nov 22nd 2008 Institute of Physics, Liverpool Evidence for Dark Matter the speed at which stars orbit round a galaxy points to the existence of a halo of dark matter. sensitive surveys show that this can not be due to stars, or gas. Nov 22nd 2008 Institute of Physics, Liverpool Evidence for Dark Matter 2 images of clusters of galaxies with HST show arcs due to gravitational lensing. These can be used to weigh the cluster. Again, the cluster is dominated by dark matter. Nov 22nd 2008 Abell 2218 Institute of Physics, Liverpool Large scale structure The 3-dimensional distribution of galaxies shows structure on different scales. This can be used to estimate the average density of the universe. In dimenionless units: Wo ~ 0.27 Nov 22nd 2008 Institute of Physics, Liverpool Need for Dark Matter So there is far more matter (Wo ~ 0.27 ) out there than can be accounted for by the stuff we are made of (Wb ~ 0.04). 85% of the matter in the universe is ‘dark’ matter (the neutralino ?) Particle Physicists hope to detect this at the Large Hadron Collider Nov 22nd 2008 Institute of Physics, Liverpool Supernovae as Standard candles Type Ia supernovae (explosion of a white dwarf star in a binary system) seem to be remarkably uniform in their light curves. They behave like ‘standard candles’ and can be used to estimate distances. Nov 22nd 2008 Institute of Physics, Liverpool Distant Type Ia supernovae Recently a breakthrough in search techniques, using 4-m telescopes to locate new supernovae, and 8-m telescopes plus the Hubble Space Telescope to follow them up, has resulted in the detection of Type Ia supernovae at huge distances. Nov 22nd 2008 Institute of Physics, Liverpool Evidence for dark energy Over 100 Type Ia supernova have been found at redshifts 0.5-1.5 Comparing these to nearby supernova, we find that in cosmological models with matter only, the distant supernovae are fainter than expected for their redshift. ‘Dark energy’ is pushing the galaxies apart. Nov 22nd 2008 Institute of Physics, Liverpool redshift, or distance What is Dark Energy ? According to Einstein’s General Theory of Relativity, there can be an extra term in the equation for gravity, which on large scales turns gravity into a repulsive force (the ‘cosmological repulsion’) This extra term, denoted L, behaves like the energy density of the vacuum, hence ‘dark energy’ So far there is no particle physics explanation for this dark energy Nov 22nd 2008 Institute of Physics, Liverpool Mapping the Cosmic Microwave Background The CMB is incredibly smooth, to one part in 100,000, but the very small fluctuations, or ‘ripples’, first mapped by the COBE mission, are the precursors of the structure we see today. They also tell us about the matter and energy present in the early universe Nov 22nd 2008 Institute of Physics, Liverpool History of the universe Nov 22nd 2008 Institute of Physics, Liverpool Origin of the universe there are speculations about the origin of the universe theoretical physicists are trying to unify gravitation (ie General Relativity) and quantum theory into a single unified ‘theory of everything’ current favourite is ‘string theory’, but so far this makes no predictions about the observed universe, instead we have the ‘string landscape’ one popular idea is ‘chaotic inflation’ - our universe arose out of a vacuum fluctuation in an infinite fluctuating void in this picture there might be many parallel universes, each with different properties - the ‘multiverse’ currently no evidence to support this idea, or the ‘anthropic principle’, which is supposed to select which type of universe we find ourselves in Nov 22nd 2008 Institute of Physics, Liverpool Fate of the universe if the current consensus model, with a dominant role for dark energy, is correct, the fate of the universe is a bleak one the distances between galaxies will increase at an ever-accelerating rate, but the horizon will remain fixed at more or less its current size, 13 billion light yrs eventually, after 100 billion years, our Galaxy will have merged with Andromeda and our other neighbours in the Local Group into a single large and dying galaxy there will be no other galaxies within our observable horizon eventually all star formation will cease, all stars will die, black holes will evaporate, and finally protons and neutrons will decay as the Greek poet Sappho put it: Nov 22nd 2008 ‘nothing will remain of us’ Institute of Physics, Liverpool The unanswerable questions • Is the universe spatially finite or infinite ? - there is a horizon defined by how far light has travelled since the Big Bang • What was there before the Big Bang ? -our theories break down before we can extrapolate to the Big Bang itself Nov 22nd 2008 Institute of Physics, Liverpool how to detect z = 10 galaxies ? James Webb Space Telescope Nov 22nd 2008 Institute of Physics, Liverpool ALMA, 2010 Nov 22nd 2008 Institute of Physics, Liverpool