black holes in astronomy - rhodes university · supermassive black holes 1969. lynden-bell argues...
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Black Holes In AstronomyBlack Holes In Astronomy
credit: NASA
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Black holes turn our intuition upside-down! But first, a bit of history
Einstein 1915:
established equations describing how matter curves space and warps time
Karl Schwarzschild 1916: found the simplest, spherically-symmetric space-time map
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Physics of an accreting Black Hole
horizon
static limit
ergosphere
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Physics of an accreting Black Hole
horizon
staticlimit
ergosphere
radiation
magneticfields
jet
jet
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Black-hole accretion simulation
McKinney & Gammie 06McKinney & Gammie 06McKinney & Gammie 06
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Making black holes from massive stars
• Mass > 25 Solar• Lives < 10 million years• Ends life with gravitational collapse forming a black hole
60 km
Stellar-mass black hole(a few times moremassive then the Sun)
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credit: NASA
• Stellar-mass black holes are “seen” only if they have a close stellar companion
• What’s observed is a very hot accretion disc
• The mass can be measured from the companion’s motion
Stellar-mass black holes
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Supermassive black holesSupermassive Black Holes
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Historical timeline:
1962. Quasars discoveredat billions of light years bySchmidt.
1964. Zeldovich & Novikovand Salpeter argue thatQuasars are powered by theaccretion of gas ontosupermassive black holes
1969. Lynden-Bell argues thatsupermassive blackholes should existat the centers of manygalaxies.
1996+. Hubble Telescope observations,analyzed using Martin Schwarzschild’s method,establish that supermassive black holes exist in the large majority of galaxies with a central bulge.
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Click to edit Master text stylesSecond level
Third levelFourth level
Fifth level
Jets and lobes of Cygnus A
Carilli et al.
Supermassive black holes are the most powerful engines in the Universe
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Jet-driven bubblesClick to edit Master text styles
Second levelThird level
Fourth levelFifth level
Allen et al. 06
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Supermassive black holes
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Relationship between SBHs and host galaxies
Black-hole mass
galacticvelocity dispersion
Gebhard etal, 00Ferrarese &Merritt 00Tremaineet al. 02
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Main question: how do SBHs form and grow tocurrent large masses (0.1 million to 10 billion solar)?
Observational answer: SBH grow from smaller seeds and acquire most of their mass by gas accretion.
1. Observe light from systems with SBH accretion (quasars and active nuclei)2. Divide by 0.3c to obtain mass3. Compare with SBH mass density in the local Universe
2
Good agreement!Soltan 1982Yu & Tremaine 2002
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Andrea Ghez,UCLA
Keck telescope, Hawaii
Black hole at the center of our Galaxy, the Milky Way.
European Southern ObservatoryVLT, Chile
Reinhard Genzel,MPE
Reinhard Genzel,MPE
Andrea Ghez,UCLA
Keck telescope, Hawaii
Supermassive Black Hole at the center of our Galaxy, the Milky Way
European Southern ObservatoryVLT, Chile
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Keck Stellar Orbits.
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VLT stellar orbits (reconstructed in 3 dimensions), of stars moving around the 4 million solar masses Supermassive Black Hole, SgrA*.
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Do black holes ever find partners?
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Stellar-mass black hole binaries
or
Marriage by attraction
Arrangedmarriage
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LIGO: will measure stellar-mass BH mergers
LIGO: will measure stellar-mass BH mergers
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Hubble Komossa et al 02 (Chandra)
Merging Galaxies Merging Supermassive black holes?
Supermassive black hole binaries
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This personal ad is from Toronto’s “Now’’magazine:
CHARM, SUBTLETY, imagination, this distinguished,40s SWPM , 6’, 200 lbs, divorced with no dependents,resembles Michael Douglas, seeks equally-slim, unattached attractive female, 32-44, for new beginnings. 910730.
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Black holes have no hair!
4 million solar mass, spin 0.6, BH is looking for other BH.
You know what we do.
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Dance and merger of black holesCaltech+CornellDance and merger of black holes
credit: Caltech+Cornell
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Binary with spinBinary without spin
Eccentric inspiral
Circular inspiralScott Hughes, MIT
“Listening” to gravitational waves from black-hole mergers
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Hubble Komossa et al 02 (Chandra)
Merging Galaxies Merging Supermassive black holes?
Supermassive black hole binaries
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Theorists dream of mergers: Begelman, Blandford, &Rees 1982:
10 kpc 2pc 1pc 0.01pc merger
Dynamicalfriction
scattering wishfulthinking
gravitationalwaves
gasnon-sphericalpotential
Anotherblack hole
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Orbital evolution: the chirp – see first lecture!
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Population of chirping sourcesAmount of time spent near frequency f
Number of sourcesin the frequency banddf scales with dt
Power spectrumfrom incoherentsuperposition
Characteristicstrain
GRprediction!!
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Gravitational waves: a (Gaussian, stochastic) background!
Phinney 01Jaffe & Backer 03Wyithe & Loeb 03Sesana et al. 07, 08, 09Ravi et al. 12
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amplitude spectralindex
General Relativity prediction:
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Conclusions
• Black holes are the most powerful engines in the Universe. They power quasars, active galactic nuclei, and (probably) gamma-ray bursts
• Binary black-hole astrophysics is on almost solid ground – very good arguments for why GW are there in the PTA band