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Searching for the Most Distant Black Holes in the Early Universe Anton Koekemoer (Space Telescope Science Institute) June 6, 2006 1 A Bit of History... 1687: Isaac Newton – what goes up, comes down... – an object moving away from the earth faster than ~25,000 mph can escape 1783: John Michell – considered speed of light (186,000 miles/second) – asked how massive an object can be until light can’t escape - first description of black hole 1796: Pierre-Simon Laplace – independently predicted the properties and possible existence of such objects 2 How are Black Holes made? • Normal stars: – the sun has 332,000 times more mass than earth – what prevents it from collapsing? • nuclear fusion reactions at its core: 15 million deg K • heat generates pressure to balance gravitational collapse • When nuclear fuel runs out, a star collapses (and explodes), leaving a remnant that is either: – white dwarf – neutron star – black hole 3 • White Dwarf: up to 1.44 Msun – “electron degenerate” matter – 1 teaspoon would weigh ~ 5 tons! – all the mass of the sun, about the size of earth... • Neutron Star: 1.44 to 2-3 Msun – “neutron degenerate” matter – 1 teaspoon would weigh ~100 million tons! – the mass of the sun, about the size of a city... 4 • Black Hole: above ~2-3 Msun – neutrons can no longer be kept apart – current physics predicts gravitational collapse to point-like “singularity” – collapse might instead be to some new form of condensed matter (eg degenerate quarks) - but still inside event horizon, thus effectively a black hole 5 • What might a black hole look like?... not quite! • Black holes can be messy - may often have disks of gas and dust around them Einstein: Gravity can bend light rays... (light has mass... E=mc2) 6 So, how do we find Black Holes?... • Black hole candidates in our own Milky Way galaxy: – – – – Cygnus X-1 Circinus X-1 SS433 ... • each one is a likely product of a supernova • display signatures too unusual for white dwarfs or neutron stars 7 • Compact objects (black holes, neutron stars) are often surrounded by “accretion disks” – – – – Gas spirals in toward the black hole heats up as it gets close emits energetic UV light and X-rays material can be ejected in “jets” Cygnus XR-1 jet 8 • Why might these objects be black holes? – Spectroscopy show that the main star revolves around their companion every few days, thus companion has mass up to 10 Msun – However, it’s invisible! - can’t be normal star – Too massive for neutron star – X-ray and UV properties can show relativistic signatures 9 • SS433: – twin “jets” – rotate with fast precession speed – likely too powerful to be neutron star 10 • Cygnus X-1 – timing measurements of UV emission from hot gas around it – gas is rotating, but with shorter rotation period each time – eventually, emission fades as gas spirals in • is only consistent with a black hole 11 • The Black Hole at the Center of our Milky Way Galaxy 12 • What is the Central Object in our Milky Way Galaxy? – Very massive: almost 4 million Msun – Compact: diameter ~14 million miles • Smaller than the orbit of Mercury! – Strong radio and X-ray emission – No optical emission: Radio image • can’t be a conventional object (massive star cluster, etc) • Black hole is the best candidate that explains the available data Chandra X-ray image 13 • MCG-6-30-15: A Galaxy with a candidate active central black hole Optical image Infra-red image X-ray spectrum 14 Observed spectrum of MCG-6-30-15 A single emission line (at 6.7 keV) is “Doppler shifted” to lower energy with velocities up to 60% the speed of light! 15 • Radio Jets!: The “Radio Galaxy” Centaurus A – distance: ~ 10 million light years 16 • Radio Jets!: The “Radio Galaxy” Centaurus A – distance: ~ 10 million light years 17 • Radio Jets!: The “Radio Galaxy” Centaurus A – distance: ~ 10 million light years 18 • Radio Jets!: The “Radio Galaxy” Centaurus A – distance: ~ 10 million light years 19 • M87, another radio galaxy with jets 20 • M87, another radio galaxy with jets 21 22 • Other active “radio galaxies”: more distant, more powerful: 3C433 Fornax A 3C66B 23 • Images in radio emission (100,000s light years) 3C353 Cygnus A 3C31 3C288 24 • A zoo of different types of active galaxies: – – – – – Seyferts Type 1, 2 quasars blazars BL Lacs Radio galaxies; Fanaroff-Riley Type I, II • Basic ingredients: – – – – – black hole accretion disk diffuse gas clouds thick torus jets (optional extra) 25 • Measuring Black Hole masses – Study stars, gas around black holes in galaxy cores – Use basic “Doppler shift” technique: • emission towards us is blue-shifted • emission away from us is red-shifted – Compare difference, measure size, get the mass! – eg black hole in M84 26 Black Hole and Galaxy Masses - A connection! 27 • What determines the BH/bulge mass relation? – do black holes “grow” along with galaxies, eg when galaxies merge? – or do black holes form as-is, early in the universe, and then fix the properties of galaxies that form around them? • These are two very different scenarios gradual growth with cosmic time vs static early-on determination • Both probably apply to some extent; therefore, aim to determine the dominant mechanism 28 • Black Holes can Grow when Galaxies Merge... 29 • Massive black holes appear to exist at the highest observed distances (earliest epochs): – more than a dozen at redshift > 6; age of the universe was less than 1 billion years – these black holes may be up to 1 billion Msun How do they grow so fast in the early universe? 30 • Track black hole growth with cosmic time • Luminosity functions: Number of objects – simply count active galaxies of different luminosities Luminosity 31 • Track the change in luminosity function at higher redshift (earlier cosmic times): – low-luminosity objects more numerous later – high-luminosity objects more numerous earlier -3 -3 Lx = 42.0 Lx = 43.0 -5 Lx = 44.0 d(phi)/d(logL) (Mpc-3) Number of objects -5 -7 -9 z = 0.015 - 0.2 -11 z = 0.2 - 0.4 Lx = 45.0 -7 Lx = 46.0 Lx = 47.0 -9 Lx = 48.0 - 11 z = 0.4 - 0.8 -13 - 13 z = 0.8 - 1.6 z = 1.6 - 3.2 z = 3.2 - 4.8 -15 41.5 - 15 0.1 42.5 43.5 44.5 45.5 Log Lx (e rg/s) Luminosity 46.5 47.5 0.6 2.4 redshift Higher redshift (earlier cosmic times) 32 • So, low-luminosity black hole nuclei reach their peak at recent cosmic times • We also know that the rate of star formation in galaxies reaches a peak at late cosmic times • One mechanism that can explain both: – minor mergers (large galaxy swallowing small galaxy, or passing interactions) • Small amounts of gas trigger star formation, and yield low luminosity black hole nuclei 33 • What about high-luminosity black holes? – reach their peak at much earlier cosmic times – suggests the fuelling mechanism may be different • One possible mechanism: – major mergers (two large galaxies colliding) – large amounts of gas fuel high luminosity black hole nuclei • How to answer this? – up till now, only had ~10 black holes at high redshifts (z ~ 6, or cosmic age < 1 billion yrs) – need to find a lot more black holes at these early epochs, to enable statistical tests 34 • How to find distant black holes... – they are very rare, so we need a large area – they are very faint, so we need to go deep... – they emit across the spectrum, so need X-ray, optical, infrared, radio, ... • do everything! deep, wide, multiband surveys 35 36 • Hubble / ACS for ~1 million seconds exposure • deepest exposures ever taken (~30th magnitude) • Very small area (~3 arcminutes on a side): – 1/10 diameter of full moon 37 38 • Two matching fields, north and south • 30 times more area than UDF • Each field is 10x16 arcminutes: – 30 times more area than UDF – about half the size of the full moon • Deepest ever X-ray and infrared exposures 39 • X-ray view of the two GOODS fields: – each is about half the size of the full moon – 1 million and 2 million seconds with Chandra South North 40 • Largest ever survey obtained with Hubble – 600 orbits (1.5 million seconds) – 2 square degrees – 10 times the area of the full moon 41 • Largest ever survey obtained with Hubble – 600 orbits (1.5 million seconds) – 2 square degrees – 10 times the area of the full moon 42 • Predicted properties of distant black holes? – should be strong X-ray sources (from hot gas) – should be strong infrared sources (from hot dust) – should have very faint (or none) optical emission 43 44 45 • These black hole nuclei appear to be at very large distances, and they are 1000x fainter than the bright quasars found previously • Compare their numbers to those found at lower redshifts (later cosmic times): 46 • Results: – find that the faint, low-luminosity black hole nuclei are indeed much rarer at these epochs – confirms the prediction that black holes in the early universe grow mostly by major mergers between galaxies – suggests that the relationship between black holes and galaxy bulge mass is also driven by mergers • Remaining question: What happens earlier??? • Next steps: – probe to redshifts > 6 (epochs < 1 billion years) – probe to fainter limits (lower-luminosity objects) 47 • The Future... Wide-Field Camera 3 – scheduled for Servicing Mission 4 (late 2007 / early 2008) James Webb Space Telescope – currently being built – scheduled for launch in 2013 48