Black Holes The Science Behind The Science Fiction

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Black HolesThe Science Behind The Science
Fiction

• Eliot Quataert (Berkeley Astronomy Dept)

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Science Fiction
A Journey That Begins Where Everything Ends
Infinite Space, Infinite Terror
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A Muse for Popular Culture
The Far Side
The giant Schilling vortex has become the black
hole of popular culture, sucking in all images
and sound and allowing only soundbites about The
Great Pitchers courage and legacy to
escape. Angry Yankees Fan
Gary Larson
Suddenly, through forces not yet fully
understood, Darren Belskys apartment became the
center of a new black hole
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(No Transcript)
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• What is a black hole?
• Do BHs exist in Nature?
• YES!
• How do we find them?
• What do they look like?

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First, Something Simpler Stars Pressure
Balances Gravity
From www.astronomynotes.com
The Sun
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Eluding Gravitys Grasp

Escape Velocity
Escape Velocity Speed Needed To Escape An
Objects Gravitational Pull
Mass M Radius R
Earth Vesc 27,000 miles/hour (11 km/s) Sun
Vesc 1.4 million miles/hour (600 km/s)
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Dark Stars 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 gt
  speed of light?
• A star we couldnt see!

Earth mass R ? 1 inch Solar mass R ? 2
miles
Vesc speed of light ?
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1915 General Relativity, Einsteins Theory of
Gravity 1916 Schwarzschilds Discovery of BHs
in GRBHs only understood accepted in the
1960s (Term Black Hole coined by John Wheeler
in 1967)
Albert Einstein
Karl Schwarzschild
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Black Holes in GR
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)
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Dispelling the Myths

• BHs are not cosmic vacuum
• cleaners only inside the horizon
• is matter pulled inexorably inward
• Far away from a BH, gravity
• is no different than for any
• other object with the same mass
• If a BH were to replace the sun, the orbits of
  planets, asteroids, moons, etc., would be
  unchanged
• (though it would get really really cold).

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How do we find BHs in Nature?
Sidney Harris
Its black, and it looks like a hole. Id say
its a black hole.
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Where are BHs Found?
Centers of Galaxies
Binary Stars
1 BIG BH per galaxy million-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
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Shedding Light on BHs X-ray Binaries
Gas falling into a BH gets very hot and emits
lots of radiation in X-rays Accretion is how we
see a black hole
Matsuda
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.

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How do we know its a BH?

• Nature is tricky couldnt it be another small
  star like a neutron star or a
  white dwarf?
• Measure mass of X-ray star by motion of its
  companion (a star like the sun)

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How do we know its a BH?

• Nature is tricky couldnt it be another small
  star like a neutron star or a
  white dwarf?
• Measure mass of X-ray star by motion of its
  companion (a star like the sun)
• Mass gt 3 solar
• masses ? BH!
• Roughly a dozen BHs found this way (tip of the
  iceberg)

Chandrasekhar
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Where are BHs Found?
Centers of Galaxies
Binary Stars
1 BIG BH per galaxy million-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
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The Milky Way Galaxy 100,000 light-years
across
Scale Size of Solar System 0.01 light-years
Typical Distance btw. Stars 1
light-year
4 106 Msun Black Hole
Central Black Hole Mass 4 million Msun
Also millions of 10 Msun BHs
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Stars in the Central Light-Year of the Galaxy
Keep Zooming In
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Evidence for a Big BH at the center of our Galaxy
Motion of stars at the center of the Milky Way
over the past decade
Genzel et al also Ghez et al.
10 light-days ? size of solar system
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Evidence for a Big BH at the center of our Galaxy
Velocities Orbits of Stars ? Mass
BH in our Galaxy weighs in at 4 MILLION SOLAR
MASSES
Genzel et al also Ghez et al.
10 light-days ? size of solar system
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Light From Gas Falling Into the Black Hole
BH
Infrared Image
X-ray Image
Analogy Solar Flare
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Many Varieties of Massive BHs
Our Galaxy
Brightness of Central Black Hole
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Active Galactic Nuclei
radio image
The BH ejects beams (jets) of matter energy
far outside its host galaxy into the surrounding
universe
The BH can outshine all of the stars in its host
galaxy!
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The Moral of the Story

• Physicists said that Black Holes could exist
• the ultimate victory of gravity over all other
  forces
• Astronomers find that BHs do exist
• 1 Big BH per galaxy ( million-billion solar
  masses)
• millions of little BHs per galaxy ( solar
  mass)
• BHs are responsible for the most dramatic and
  energetic phenomena in the universe
• BHs are seen via the light produced by
  infalling gas via the gravitational
  pull that they exert on nearby objects