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A GOLDEN AGE OF ASTRONOMY - giant telescopes, space missions and invisible wavelengths Michael Rowan-Robinson Imperial College London Sept 27th 2008 Thessaloniki 50 years of the new astronomy The past 50 years has seen a transformation of astronomy from the study of visible radiation with optical telescopes, to the study of all electromagnetic radiation, with the emergence of first radioastronomy, then X-ray astronomy, ultraviolet, gamma-ray, infrared and submillimetre astronomy - the invisible wavelengths. This development has been made possible by a combination of detector advances and the construction of giant telescopes both on the ground, often on high mountain-tops, and in space. With these advances has come a new understanding of stars and galaxies, and of the universe we inhabit. And a host of exotic new phenomena - quasars, pulsars, black holes, exoplanets. Sept 27th 2008 Thessaloniki the birth of modern cosmology Our modern picture of the universe can be said to date from 1929, when Edwin Hubble discovered the expansion of the universe. This breakthrough, like many of the major advances in our understanding of the universe, including the very latest discovery of ‘dark energy’ (see later), can be connected to advances in our ability to measure distance in the universe. Sept 27th 2008 Thessaloniki First steps on the distance ladder Aristotle (384-322 BC) - estimated the size of the earth (+ Eratosthenes, Poseidonius, 10%) Hipparcos (2nd C BC) - estimated distance of the moon (59 RE, cf modern value 60.3) and tried to estimate the distance of the sun Sept 27th 2008 Thessaloniki Aristotle, by Raphael The Copernican revolution Copernicus (1473-1543) - gave the correct relative distances of the sun and planets - absolute value not determined accurately till the 19th century - stars had to be much further away than for earth-centred model (Aristarchos, Archimedes) Sept 27th 2008 Thessaloniki The first steps outside the solar system Bessel 1838 - discovered parallax of nearby star 61 Cyg, its change in apparent direction on the sky due to the earth’s orbit round the sun (the final proof of the Copernican system) Sept 27th 2008 Thessaloniki The key modern distance indicator – Cepheid variable stars Delta Cephei is the prototype of the Cepheid variable stars, massive stars which pulsate and vary their light output Sept 27th 2008 Thessaloniki Henrietta Leavitt’s breakthrough In 1912, Henrietta Leavitt, working at the Harvard Observatory, discovered from her studies of Cepheids in the Small Magellanic Cloud that the period of Cepheid variability was related to luminosity Sept 27th 2008 Thessaloniki The distances of the galaxies In 1924 Edwin Hubble used Leavitt’s discovery 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. Sept 27th 2008 Thessaloniki The Palomar 5-m telescope Hubble used the Mount Wilson100-inch telescope and, later, the Mount Palomar 200-inch telescope, shown here. Sept 27th 2008 Thessaloniki 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). Sept 27th 2008 Thessaloniki first detection of electromagnetic radiation outside the optical band: Herschel (1800) detected infrared radiation from the sun Atmospheric transmission Sept 27th 2008 Thessaloniki Radio astronomy •1933 Karl Jansky, detected Milky Way at radio wavelengths •1940s Grote Reber, mapped the Milky Way • 1945, John Hey, discovered point sources • 1955-65 Cambridge, Parkes, surveyed the sky and catalogued extragalactic radio sources - radio-galaxies and quasars • 1967 discovery of pulsars Sept 27th 2008 Thessaloniki X-ray astronomy from space •1948 T.R.Burnight detects X-rays from sun using V2 •1962 Giacconi detects X-ray binary Sco-X1 using Aerobee rocket •1963 Boyer detects Crab Nebula in X-rays (rocket) •1965 first extragalactic X-ray source (M87, Byram, rocket) •1970 Uhuru X-ray satellite maps sky at 2-20 KeV many subsequent X-ray missions, through to Chandra and XMM, both launched in 1999 (Paul Nandra and Ioannis Georgantopoulos will talk about these) Sept 27th 2008 The Uhuru satellite before launch Thessaloniki Uhuru 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 degree) Sept 27th 2008 Thessaloniki IRAS 1983 saw the launch of IRAS, the Infrared Astronomical Satellite, which made the first all-sky survey at infrared wavelengths, from 10-100 microns Sept 27th 2008 Thessaloniki The launch of IRAS Sept 27th 2008 Thessaloniki IRAS - the infrared ‘cirrus’ emission from clouds of interstellar dust in our Galaxy Sept 27th 2008 Thessaloniki south celestial pole IRAS - star forming regions LMC, the Large Magellanic Cloud Sept 27th 2008 Thessaloniki 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 Sept 27th 2008 Thessaloniki 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 150 exoplanets are known. Sept 27th 2008 Thessaloniki IRAS the IRAS all-sky survey of infrared point-sources: white: star-forming regions, blue: red giant stars, green: galaxies Sept 27th 2008 Thessaloniki the William Herschel Telescope on La Palma, used to follow up IRAS galaxies Sept 27th 2008 Thessaloniki Mapping the Universe Sept 27th 2008 Thessaloniki 3-D map of the galaxy distribution, constructed from IRAS galaxy redshift survey Sept 27th 2008 Thessaloniki 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 Sept 27th 2008 Thessaloniki The Hubble Space Telescope (1989) 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. Sept 27th 2008 Thessaloniki Some of the galaxies studied by the Hubble Space Telescope Sept 27th 2008 Thessaloniki The HST Key program final result Ho = 72 km/s/Mpc uncertainty 10% (Freedman 2001) log V Sept 27th 2008 Thessaloniki 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) Sept 27th 2008 Thessaloniki 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 Sept 27th 2008 Thessaloniki 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 Sept 27th 2008 Thessaloniki 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. Sept 27th 2008 Thessaloniki 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 Sept 27th 2008 Thessaloniki 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. Sept 27th 2008 Thessaloniki 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. Sept 27th 2008 Abell 2218 Thessaloniki 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 (switch-on Sept 10th) Sept 27th 2008 Thessaloniki Sept 27th 2008 Thessaloniki Kitt Peak, Arizona, 1974, my first observing run JCMT 1987 Sept 27th 2008 Thessaloniki first submillimetre survey of the sky, using JCMT. several very luminous galaxies found - galaxies in the midst of their main star and heavy element formation. Sept 27th 2008 Thessaloniki the NASA Great Observatories HST 1990 CHANDRA 1999 COMPTON 1991 Sept 27th 2008 Thessaloniki SPITZER 2003 Sept 27th 2008 Thessaloniki SPITZER, 2003 LMC Sept 27th 2008 Thessaloniki 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 Sept 27th 2008 Thessaloniki QuickTime™ and a MPEG-4 Video decompressor are needed to see this picture. Sept 27th 2008 Thessaloniki infrared emission from debris along a comet orbit Sept 27th 2008 Thessaloniki visible (HST) and infrared (Spitzer) images of M51, the ‘Whirlpool’ galaxy Sept 27th 2008 Thessaloniki Sombrero galaxy Sept 27th 2008 Thessaloniki Two interacting galaxies Sept 27th 2008 Thessaloniki Visible and infrared images of the star-forming galaxy Messier 82 Sept 27th 2008 Thessaloniki 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. Sept 27th 2008 Thessaloniki 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. Sept 27th 2008 Thessaloniki Keck and VLT (Very Large Telescopes) Sept 27th 2008 Thessaloniki examples of Supernovae Sept 27th 2008 Thessaloniki 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 (Perlmutter 2002). ‘Dark energy’ is pushing the galaxies apart. Sept 27th 2008 Thessaloniki 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 Sept 27th 2008 Thessaloniki 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 (Andrew Jaffe will say more about this) Sept 27th 2008 Thessaloniki History of the universe Sept 27th 2008 Thessaloniki 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 Sept 27th 2008 Thessaloniki 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: Sept 27th 2008 ‘nothing will remain of us’ Thessaloniki 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 Sept 27th 2008 Thessaloniki near future European Space Agency missions Herschel Mar 2009 Planck Mar 2009 GAIA Dec 2011 BepiColumbo Aug 2013 JWST June 2013 (jointly with the US) Sept 27th 2008 Thessaloniki how to detect z = 10 galaxies ? James Webb Space Telescope Sept 27th 2008 Thessaloniki ALMA, 2010 Sept 27th 2008 Thessaloniki