Black Holes

• Regions of space from which nothing, not even light, can escape because gravity is so strong.• First postulated in 1783 by John Michell• Term “black hole” coined in 1969• Observational evidence starting in 1970s

We see the effects ablack hole has on matter and radiation

near it; we have not yet seena black hole directly.

Journey to a Black Hole

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Black Hole Structure

Schwarzschild radius defines the event horizon

Rsch = 2GM/c2

Singularity is “clothed” inside the event horizonCosmic censorship prevails (you cannot see inside the event horizon) Schwarzschild BH

What is This?

• Diagram of the effect of gravity(gravitational potential well)near the black hole on the fabric of spacetime

• It is a 2-D depiction of a 3-Devent

Types of Black Holes

Primordial – can be any size, including very small (If <1014 g, they would still exist)

Stellar Mass – must be at least 3 solar masses (~1034 g)

Intermediate Mass – a few thousand to a few tens of thousands of solar masses; possibly the agglomeration of stellar mass holes

Supermassive – millions to billions of solar masses; located in the centers of galaxies

The First “First” Black HoleCygnus X-1 binary systemMost likely mass is 16 (+/- 5) Mo

Mass determined by Doppler shift measurements of optical lines

NGC 4261

100 million light years away

1.2 billion Mo black hole in a region the size of our Solar SystemMass of disk is 100,000 Mo

Disk is 800 light years across

Supermassive Black Holes

Rotating black hole in the center of a galaxy, which is emitting relativistic jets of material

Emission is from just outside the event horizon

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Active Galaxies

Jets of fast moving particles and gamma-rays

Disk of galaxy with supermassive blackhole in center

Halo of gas, and dust

Quasars, Blazars, Seyferts, AGN, ….etc, etc, etc

Radio & Optical Image of an AGN

NGC 4261

Deep Image

Black Holes Are Everywhere!

Black holes in quasars

QSO

Galaxy

Empty

Black holes in“normal” galaxies

Black holes in empty space

Chandra deep field

Galactic Black Hole

Zooms in to show the region surrounding the black hole in the center of a galaxy Accretion disk of gas swirls around black hole

Galactic Black Holes

NGC 3377 & NGC 4486b are 2.7 arc-sec imagesNGC 3379 is 5.4 arc seconds Note double nucleus in central 0.5 arc-sec of NGC 4486b

Colliding BHsSpiral waveform can be calculated reliablyRingdown after merger tells you the massLarger computers needed to predict the actual collision waveforms

Gamma-ray Bursts!

Most powerful explosions in the Universe today - and one of the greatest mysteries of modern astrophysics

“When you see a gamma-ray burst, a black hole is being born” – M. Livio

Gamma-ray Astronomy(The Short, Short Story…)

Sources of -ray Emission

• Black holes• Active Galaxies• Pulsars• Gamma-ray bursts• Diffuse emission• Supernovae• Unidentified

GRBs: The Very Brief Version

• Humble Beginnings: A Bomb or Not a Bomb? Vela Program

• A few hundred events, a few hundred theories

• Finally, science to the rescue Compton Gamma Ray Observatory BeppoSAX/ROTSE/HST/ (and a host of others)

Vela Program

CGRO

Gamma-Ray Bursts

Distribution of GRBs in the Sky

What BeppoSAX Saw

What HST Saw (Much Later)

Breakthrough!

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Models for GRBs

HypernovaMerging Neutron Stars

Come On…Let’s Vogue

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What’s Next

New Missions = Better Data

Improved theory

Serendipity

New Missions = Better Data

Swift (2003) GLAST (2005)

HETE II (launched 7 October 2000) INTEGRAL (2001)

Swift

Imagine…we have detected a GRB!

Our gamma-ray detector measures 5.27 x 10 -6 ergs/cm2

Hey, Laura!

What’s so impressive about that?!??!!!

Wrapping Up the Universe

The light we measure decreases as a function of distance,

We can find a galaxy’s distance if we can measure its velocity from its redshift,

By measuring the distances of gamma-ray bursts from their redshifts, we can see how amazingly powerful these events are.

Remember the Falloff of Light

What you detect =

What was emitted

4 D2

Remember Hubble’s Law

v = Ho * d Ho is called the Hubble constant. It is generally believed to be around 65 km/sec/Mpc.

Remember the Doppler Shift

=

vc

=z =

And Now for a Real Spectrum...

This is an optical spectrum of a GRB from Keck, the world’s largest optical telescope. The locations of several Doppler shifted spectral lines are shown.

A Little Musical Interlude

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A BIG Hint: From Redshift to Power

Step-by-step power calculation:

1. Measure the redshift of three spectral lines2. Take the average redshift, z3. From this, calculate the velocity v=z*c4. Using the Hubble Constant, get the distance

d=v/Ho

5. Convert distance in Mpc to distance in cm6. Now, with the distance to the GRB, and the

value measured at our detector, calculate power: P=4πd2*measured flux

1 Mpc ~ 3 x 10 19 km

L = 5.3 x 10-6 ergs/cm2

Needed Information

GRBs

are the most

in the Universe!