Black HolesBlack HolesThe Science Behind The Science FictionThe Science Behind The Science Fiction

Science FictionScience Fiction

“Infinite Space, Infinite Terror”

“A Journey That Begins Where Everything Ends”

A Muse for Popular CultureA Muse for Popular Culture

The giant Schilling vortex has become the black hole of popularculture, sucking in all images and

sound and allowing only soundbitesabout The Great Pitcher’s courage

and legacy to escape.

Angry Yankee’s Fan

“Suddenly, through forces not yet fully understood, Darren Belsky’s apartment became

the center of a new black hole”

The Far Side

What is a black hole?What is a black hole?

Do BHs exist in Nature?Do BHs exist in Nature?– YES!YES!

How do we find them?How do we find them?What do they look like?What do they look like?

First, Something Simpler: Stars First, Something Simpler: Stars Pressure Balances GravityPressure Balances Gravity

The Sun

From

ww

w.astronom

ynotes.com

Eluding Gravity’s GraspEluding Gravity’s Grasp

Earth: Vesc = 27,000 miles/hour (11 km/s)Sun: Vesc = 1.4 million miles/hour (600 km/s)

 

Vesc =2GMR

Mass MRadius R

Escape VelocityEscape Velocity

Speed Needed ToEscape An Object’s

Gravitational Pull

““Dark Stars”Dark Stars” Rev. John Michell (1783) & Pierre-Simon Laplace (1796)Rev. John Michell (1783) & Pierre-Simon Laplace (1796)

Speed of light 1 billion miles/hour (3x105 km/s)

What if a star were so small, escape speed > speed of light?

A star we couldn’t see!A star we couldn’t see!

Earth massEarth mass: : R R 1 inch 1 inchSolar massSolar mass: : R R 2 miles 2 miles

Vesc = speedof light

1915: General Relativity, Einstein’s Theory of Gravity 1915: General Relativity, Einstein’s Theory of Gravity 1916: Schwarzschild’s Discovery of BHs in GR1916: Schwarzschild’s Discovery of BHs in GRBHs only understood & accepted in the 1960sBHs only understood & accepted in the 1960s

(Term “Black Hole” coined by John Wheeler in 1967) (Term “Black Hole” coined by John Wheeler in 1967)

Karl SchwarzschildAlbert Einstein

If an object is small enough, gravity overwhelms pressure and the object collapses. Gravity is so strong that nothing, not even light, can escape.

“Radius” of a BH 2 miles for a solar mass 1 inch for an Earth mass

NOT a solid surface

All Mass at the Center (GR not valid there)

Black Holes in GRBlack Holes in GR

Dispelling the Myths …Dispelling the Myths …

BHs are BHs are notnot cosmic vacuum cosmic vacuum

cleaners:cleaners: only inside the horizon only inside the horizon is matter pulled inexorably inwardis matter pulled inexorably inward

Far away from a BH, gravity Far away from a BH, gravity isis no differentno different than for any than for any other object with the same massother object with the same mass

If a BH were to replace the sun, the orbits of planets, If a BH were to replace the sun, the orbits of planets, asteroids, moons, etc., would beasteroids, moons, etc., would be unchangedunchanged(though it would get really really cold).

How do we find BHs in Nature?How do we find BHs in Nature?

“It’s black, and it looks like a hole. I’d say it’s a black hole.”

Sid

ney H

arris

Where are BHs Found?Where are BHs Found?

Centers of Galaxies Binary Stars

1 BIG BH per galaxymillion-billion x mass of sun

formation not fully understood

millions of ‘little’ BHs per galaxy ~ 10 x mass of sun

formed by collapse of a massive star

Shedding Light on BHs: X-ray BinariesShedding Light on BHs: X-ray Binaries

If two stars orbit close enough to each other, mass gets pulled from one and falls (accretes) onto the

other. The smaller the target object, the faster the gas moves and the hotter it gets.

Gas falling into a BH gets very hotvery hot and emits lots of

radiation in X-rays

Accretion is how we “see” a black hole

How do we know it’s a BH?How do we know it’s a BH?Nature is tricky: couldn’t it be another “small Nature is tricky: couldn’t it be another “small star” like a neutron star or a white dwarf?star” like a neutron star or a white dwarf?

Measure mass of “X-ray star” by motion of its Measure mass of “X-ray star” by motion of its companion (a star like the sun) companion (a star like the sun)

How do we know it’s a BH?How do we know it’s a BH?Nature is tricky: couldn’t it be another “small Nature is tricky: couldn’t it be another “small star” like a neutron star or a white dwarf?star” like a neutron star or a white dwarf?

Measure mass of “X-ray star” by motion of its Measure mass of “X-ray star” by motion of its companion (a star like the sun) companion (a star like the sun)

Mass > 3 solarMass > 3 solar masses masses BH! BH!

Roughly a dozen BHs found this way (tip of the iceberg)Roughly a dozen BHs found this way (tip of the iceberg)

Chandrasekhar

Where are BHs Found?Where are BHs Found?

Centers of Galaxies Binary Stars

1 BIG BH per galaxymillion-billion x mass of sun

unclear how they form

millions of ‘little’ BHs per galaxy ~ 10 x mass of sun

formed by collapse of a massive star

The Milky Way Galaxy: ~ 100,000 light-years acrossThe Milky Way Galaxy: ~ 100,000 light-years across

4 106 Msun

Black Hole

Scale: Size of Solar System: 0.01 light-years Typical Distance btw. Stars: 1 light-year

Central Black Hole Mass: 4 million Msun

Also ~ millions of 10 Msun BHs

Stars in the Central Stars in the Central Light-Year of the GalaxyLight-Year of the Galaxy

Keep Zooming In …

Evidence for a Big BH at the Evidence for a Big BH at the center of our Galaxycenter of our Galaxy

10 light-days size of solar system

Genzel et al; also G

hez et al.

Motion of starsat the center of the Milky

Way over the past decade

Evidence for a Big BH at the Evidence for a Big BH at the center of our Galaxycenter of our Galaxy

10 light-days size of solar system

BH in our Galaxy weighs in at 4 MILLION

SOLAR MASSES

Velocities & Orbitsof Stars Mass

Light From Gas FallingLight From Gas Falling Into the Black Hole Into the Black Hole

X-ray ImageInfrared Image

BH

Analogy: Solar Flare

Many Varieties of Massive BHsMany Varieties of Massive BHs

Our Galaxy

Bri

ghtn

ess

of C

entr

al B

lack

Hol

e

“Active Galactic Nuclei”

The BH can outshine all of the stars in its host galaxy!

The BH ejects beams (“jets”) of matter & energy far outside its host galaxy into the surrounding universe

radio image

The Moral of the Story …The Moral of the Story …

Physicists said that Black Holes Physicists said that Black Holes couldcould exist exist

– the ultimate victory of gravity over all other forcesthe ultimate victory of gravity over all other forces

Astronomers find that BHs Astronomers find that BHs dodo exist exist

– 1 1 BigBig BH per galaxy (~ million-billion solar masses) BH per galaxy (~ million-billion solar masses)

– millions of millions of littlelittle BHs per galaxy ( ~ solar mass) BHs per galaxy ( ~ solar mass)

BHs are responsible for the most dramatic and BHs are responsible for the most dramatic and energetic phenomena in the universe energetic phenomena in the universe

– BHs are “seen” via the light produced by infalling gas & via BHs are “seen” via the light produced by infalling gas & via the gravitational pull that they exert on nearby objectsthe gravitational pull that they exert on nearby objects