Black Holes

Black holes from the first stars to the Milky Way Marta Volonteri Astronomy Dept. University of Michigan

1. Intro: MBHs? Why? When? How? 2. When: a bit of cosmology 3. How: paths leading to MBH formation 4. How: growing black holes MBH=Massive Black Hole

Black holes? The escape velocity from a black hole is larger than the speed of light: the INSIDE of a black hole is

invisible Astrophysical black holes are described by 2 parameters only: MASS and SPIN They’re the simplest objects in the Universe

Units of measure:

length: parsec (pc) =3x1013 km=206,264 Earth-Sun distance light year: distance light travels in 1 year=63,000 Earth-Sun distance

mass: mass of the sun (Msun)=2x1033g= 1,000,000 Earth mass

luminosity (energy per unit time): minosity of the sun (Lsun)=1024 W=too many lightbulbs to count!

length: 10 kpc ∼ 32,600 light years 1012

mass: solar masses => one trillion suns!

1010

luminosity: solar luminosities

What is a galaxy made of? Halo: dark matter Disc: gas+stars Bulge: stars

Special objects: quasars short for Quasi Stellar objects appear to be point sources in the sky (pre-Hubble Space Telescope era)

QUASARS: 1. they are as luminous as galaxies: L∼1011-1013 Lsun 2. brightness varies on short timescales (<1 week)

3. information is carried at the speed of light from one side to the other of the source:

Size=c x time the emitting region is <1 light week 1,000,000 times smaller than a galaxy. NOT galaxies!

Quasars are powered by black holes accreting matter 1. they are as luminous as galaxies: L=ε M c2/time∼1011-1013 Lsun 2. stars: nuclear fusion ε=0.007 3. lifetime ∼107 years ⇒ M∼108 Msun ⇒ NOT stars! The implication is the existence of black holes with masses of millions to billions of Msun accretion onto a BH:

ε=0.1-0.4

Stellar mass BHs ✔formation through stellar evolution ✔mass < few tens Msun

Massive BHs ✔ powering quasars ✔ mass > 106 Msun

Where are these Massive Holes? We can see massive black holes as quasars when they are eating up some matter... but this not the whole time!

Hubble Deep Field-North all galaxies

Chandra Deep Field-North active galaxies

MBHs in local galaxies BHs dominate the motions of stars and gas in a tiny volume “Sphere of influence” Galaxy Size ~10-50 kpc

MBHs in local galaxies The best example of search for a SMBH is the MILKY WAY: individual stars can be resolved

Massive black holes were also found in the centers of neighboring galaxies: a demography of MBHs

MBHs and galaxies MBHs∼ 106-109 Msun tiny BHs know about big bulges!

MBH x1000

BULGE

MBHs and galaxies MBHs∼ 106-109 Msun MBH x1000

BULGE

tiny BHs know about big bulges! Rsch=2GMBH/c2 MICROPARSEC

Rinf=GMBH/σ2 PARSEC

Rbulge∼GMbulge/σ2 KILOPARSEC

Rhalo∼GMhalo/σ2 MEGAPARSEC

σ∼100 km/s c=3x105 km/s Mbulge∼103 MBH Mhalo∼10-103 Mbulge

length: 10 kpc ∼ 32,600 light years 1012

mass: solar masses => one trillion suns!

1010

luminosity: solar luminosities

What is a galaxy made of? Halo: dark matter Disc: gas+stars Bulge: stars

WHEN do you make a massive black hole?

Quasars have been detected at very large distances, corresponding to a very young age of the Universe

Light, although fast, travels at a finite speed. It takes: • 8 minutes to reach us from the Sun • 32,000 years to reach us from the edge of the Milky Way

The farther out we look into the Universe, the farther back in time we see!

Quasars have been detected at very large distances, corresponding to a very young age of the Universe D= c x time Measure D, get time:12.9 billion years ago! Age of the Universe: 13.7 billion years As massive as the largest MBHs today, but when the Universe was only 1 billion years old!

1. Intro: MBHs? Why? When? How? 2. When: a bit of cosmology 3. How: paths leading to MBH formation 4. How: growing black holes

Cosmological structure formation The universe after the Big Bang was not completely uniform Gravitational instability caused matter to condense until small regions become gravitationally bound

They then break away from the global expansion, collapse down on themselves, and form a galaxy at the center

This is what we see in cosmological simulations.... Hierarchical Galaxy Formation: small galaxies collapse first and merge later to form more massive systems

1. Intro: MBHs? Why? When? How? 2. When: a bit of cosmology 3. How: paths leading to MBH formation 4. How: growing black holes

HOW can you make a massive black hole ‘seed’?

HOW can you make a (super)massive black hole @ z≈10-30? Direct contraction of a gas cloud into a BH encounters a couple of problems: 1. ANGULAR MOMENTUM TRANSPORT Because of angular momentum, collapsing gas clouds become rotationally supported at 106-8 Schwarzschild radii → stops collapsing 2. STAR FORMATION Instead of going into BH formation, the gas can fragment and form stars and SNe can blow away the gas reservoir

PopIII star remnant DM

DM

gas

gas One star per galaxy! ~100-200 times larger than the sun

e the first stars massive enough to collapse into MBH

HOW can you make a black hole seed? MBH∼100 Msun PopIII stars remnants (Madau & Rees 2001, Volonteri, Haardt & Madau 2003)

✔Simulations suggest that the first stars are massive M∼100-600 Msun (e.g., Abel et al. Bromm et al.)

✔Metal free dying stars with M>260Msun leave remnant BHs with Mseed≥100Msun (Fryer, Woosley & Heger)

MBH ∼103-105 Msun Direct collapse: gas-dynamics (e.g. Haehnelt & Rees 1993, Eisenstein & Loeb 1995, Bromm & Loeb 2003, Koushiappas et al. 2004, Begelman, Volonteri & Rees 2006, Lodato & Natarajan 2006)

✔Transport angular momentum on the dynamical timescale ✔Cocoon of dense gas within which BH forms

DM

Gas-dynamical direct collapse

gas

DM gas

unstable

HOW can you make a black hole seed? MBH∼100 Msun PopIII stars remnants (Madau & Rees 2001, Volonteri, Haardt & Madau 2003)

✔Simulations suggest that the first stars are massive M∼100-600 Msun (e.g., Abel et al. Bromm et al.)

✔Metal free dying stars with M>260Msun leave remnant BHs with Mseed≥100Msun (Fryer, Woosley & Heger)

MBH ∼103-105 Msun Direct collapse: gas-dynamics (e.g. Haehnelt & Rees 1993, Eisenstein & Loeb 1995, Bromm & Loeb 2003, Koushiappas et al. 2004, Begelman, Volonteri & Rees 2006, Lodato & Natarajan 3007)

✔Transport angular momentum on the dynamical timescale ✔Cocoon of dense gas within which BH forms

Runaway collapse: stellar dynamics (Devecchi & Volonteri 2008)

✔Form dense stellar cluster at low metallicity ✔Stars merge into a “super-star”, collapse into BH

DM

Stellar-dynamics DM

gas gas unstable Collisio ns Runawa y growth

star cluster formation

1. Intro: MBHs? Why? When? How? 2. When: a bit of cosmology 3. How: paths leading to MBH formation 4. How: growing black holes

So, how do these black hole seeds grow?

Mseeds ∼104 Msun

MMBH∼106-9 Msun

MBHs are grown from protogalactic BH seeds.

protogalaxies

These seeds are incorporated in larger and larger galaxies,

time

along the cosmic merger history.

local galaxy protogalaxies

local galaxy

The seeds at z>20 are small, ∼100-104 Msun How do MBH seeds grow to become supermassive? supermassive BH-BH mergers vs gas accretion

courtesy of L. Mayer

GRAVITATIONAL WAVES

QUASARS

SMBHs and their detectability ElectroMagnetic bands

Gravitational Waves:

QUASARS

MERGERS

QUASARS

And now some exotic stuff... MBHs mergers and gravitational waves

Gravity is spacetime curvature. Any mass/energy bends spacetime near it. Rapidly moving masses generate fluctuations in spacetime curvature:

gravitational waves When a gravitational wave passes through, space is stretched and squeezed alternately.

Dynamical evolution of BH pairs

Gravitational rocket binary center of mass recoil during coalescence due to asymmetric emission of GW

«vesc from today galaxies

≈v

from high-z galaxies

esc

• When a gravitational wave passes through, space is stretched and squeezed alternately. • The effect is opposite in perpendicular directions.

• Measure the stretching of spacetime ΔL using lasers

space based interferometer: LISA Joint NASA/ESA mission

ΔL=10-8 cm for L=5 million km Measuring the diameter of a human hair at the distance of Mars from the Earth!

Black holes from the first stars to the Milky Way ✔ forming the seeds: stellar remnants or collapsed

galaxy cores?

✔ growing the seeds! ✔ how we test our predictions: observational

signatures