Active Galactic Nuclei

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The Accelerating Universe
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The Hubble Law

• According to the Hubble Law, the space between
  the galaxies is constantly increasing, with
  Velocity H0 D istance

By observing how the expansion rate has changed
over time, we can measure how much effect gravity
has had on the universe, i.e., its deceleration.
When we do this with supernovae, we find
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The Accelerating Universe!!!

The universe is not slowing down at all. In
fact, its speeding up!!! We live in an
accelerating universe! Its as if theres
another force pushing the universe apart a
Cosmological Constant!!!
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The Accelerating Universe!!!

Whatever this force is, we think that it is
growing stronger as the universe evolves. The
more empty space in the universe, the greater the
acceleration as if the vacuum of space has
pressure!
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The Accelerating Universe!!!

Whatever this force is, we think that it is
growing stronger as the universe evolves. The
more empty space in the universe, the greater the
acceleration as if the vacuum of space has
pressure!
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The Accelerating Universe!!!
We appear to live in a universe with a flat
shape, but which will go on accelerating
forever. The universe is 13.7 billion years old,
and is now dominated by Dark Energy. And it will
only get worse the more empty space, the more
Dark Energy.
This explains the age mismatch between globular
clusters and the universe. The universal
expansion is getting faster!
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The Accelerating Universe!!!
We appear to live in a universe with a flat
shape, but which will go on accelerating
forever. The universe is 13.7 billion years old,
and is now dominated by Dark Energy. And it will
only get worse the more empty space, the more
Dark Energy.
The Dark Energy even dwarfs dark matter!
Regular matter is really insignificant. We
really dont know anything about whats going on!!
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What is the Dark Energy?
Were clueless. There is one traditional
theory that particles and anti-particles are
constantly being created and annihilated in the
empty space (due to the uncertainty principle).
For the instant these particles exist, they would
act as a repulsive force. But our estimate of
this force is off by a factor of 10122.
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History of the Universe

• The Big Bang occurred 13.7 billion years ago.
  Since then
• 9,000,000,000 years Birth of the Sun

• 2,000,000,000 years era of galaxy
  formation/interaction
• 400,000,000 years Milky Way begins to form
• 100,000 years release of the microwave
  background

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Helium in the Universe

• If the universe began as a high density soup of
  protons and neutrons, some of those particles
  must have undergone fusion.

In the Big Bang, about 1 of every 10 hydrogen
atoms should have been changed to helium. Thats
almost exactly the helium abundance we observe
for the universe!
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History of the Universe

• The Big Bang occurred 13.7 billion years ago.
  Since then
• 9,000,000,000 years Birth of the Sun

• 2,000,000,000 years era of galaxy
  formation/interaction
• 400,000,000 years Milky Way begins to form
• 100,000 years release of the microwave
  background
• 3 minutes fusion of hydrogen to helium ends
• 0.00001 seconds protons, neutrons form
• 10-12 seconds particles form and annihilate
• 10-35 seconds quarks form gravity begins to
  exist
• 10-43 seconds ???? Grand unification

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In the First 10-35 Seconds

• Why is the universe flat?
• Why does one side of the sky look like the other
  side of the sky? (They were never in contact
  with each other.)
• Why are there no monopoles? (Magnets always have
  a north pole and a south pole.)

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Inflation

• A theory which explains these puzzles (and
  others) is that, very early on (10-35 sec after
  the beginning), the universe expanded much faster
  than now (1030 instead of 64). This is called
  inflation. The universe we see now is just a
  small region of a bubble. It therefore just
  looks flat.

(the observable universe is in red)
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Multiverses

• Inflation allows that our bubble may not be the
  only bubble. Bubbles may be forming all the time
  in a multi-universe.

(But these other universes can never be observed.)
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Multiverses

• Inflation allows that our bubble may not be the
  only bubble. Bubbles may be forming all the time
  in a multi-universe.

(But these other universes can never be observed.)
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Active Galactic Nuclei or The Monster Within
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The Discovery

• In 1962, Cambridge University just completed a
  radio survey of the sky. Maarten Schmidt took
  their radio positions and looked for optical
  counterparts. He found a few peculiar radio
  stars.

3C 273 looked like an ordinary, fairly-bright
star (with possibly a little fuzz). But ordinary
stars do not emit much in the radio part of the
spectrum.
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The Spectrum
The spectrum of the star was odd. It had

• Emission lines instead of absorption lines
• Broad (10,000 km/s) emission lines, instead of
  narrow lines
• Emission lines at strange wavelengths

The solution the emission lines were those of
hydrogen, but at enormous redshift. The object
was moving away at 10 of the speed of light!
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Quasars

• Properties of quasi-stellar radio sources
  (quasars, or QSOs)
• Star-like appearance (with possibly some jets)
• Emission-line spectra with internal motions of
  10,000 km/s
• Does not emit as a blackbody (at least, not at a
  single temperature). The objects emit light in
  x-rays, ultraviolet, optical, infrared, and
  sometimes microwave and radio
• Irregularly variable on timescales of days/months
• Enormous redshifts (can be more than 90 of the
  speed of light)
• Stars in the Milky Way cannot move that fast.
  The only way to achieve such a redshift is
  through the Hubble Law. So, through v H D,
  the objects must be incredibly far away. They
  are therefore incredibly bright as bright as
  1000 supernovae.

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Size and Variability

• Since many quasars vary in brightness we have a
  crude way to estimate their size.

• Imagine that there is some mechanism near the
  center of the QSO that controls the objects
  brightness. It says get bright.
• That command goes forth no faster than the speed
  of light.
• Within a few months, the object gets bright.
• Since no signal can go faster than the speed of
  light, the object must be no bigger than a few
  light-months across!

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The Energy Source

• What can outshine 1000 supernovae for millions
  of years, and be just slightly larger than our
  Solar System? Theoretically, not much only a
  very, very big black hole.

• Start with a 10,000,000,000 M? black hole
• Have a star come close enough to be tidally
  disrupted
• Have the material form into an accretion disk.
  Energy is released via the friction in the disk.
  If you accrete 1 M? per year, the friction you
  get will produce the luminosity of a quasar.

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Feeding the Monster
If a star comes too close, the enormous gravity
of the black hole will cause tides on the star
and rip it apart. Some of that material will be
trapped in orbit about the hole.
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Feeding the Monster
If a star comes too close, the enormous gravity
of the black hole will cause tides on the star
and rip it apart. Some of that material will be
trapped in orbit about the hole.
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Explaining a Quasars Properties

• Near the event horizon, the gas is moving close
  to the speed of light. Any emission lines which
  are produced will be broad.
• Because of the high speed of the gas, there is a
  lot of friction in the disk. A lot of light is
  produced.

• The temperature of the disk depends on the speed
  of the gas. Near the event horizon, the friction
  produces x-rays. At larger radii, where the gas
  revolves more slowly, optical and infrared light
  is made.

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Black Holes and Jets
As matter accretes onto the black hole, particles
can get ejected out the poles of the system at
99.999 of the speed of light. How this occurs
is almost a complete mystery. But its often
observed.
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Where are the Quasars Today?
The nearest quasar is 25 of the way across the
universe most belong to an era when the
universe was only 15 of its present age. If
supermassive black holes existed then, where they
now?
In the centers of galaxies!
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The Quasar-Galaxy Connection

• When a supermassive black hole is accreting, it
  can be thousands of times brighter than its
  surrounding galaxy. On the other hand, if the
  black hole is not accreting, it will be invisible.

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Active Galactic Nuclei

• Many nearby galaxies have some activity in their
  nucleus they may have an extremely bright
  nucleus, or show a jet of emission, or have broad
  emission lines, or emit at radio wavelengths.
  These objects (which are probably just accreting
  a little mass) are said to have an Active
  Galactic Nucleus.
• The energy produced by an AGN is still often many
  times that of the stars.

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Galaxies with Active Galactic Nuclei
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Sleeping Monsters

• When a black hole is not accreting matter, then
  its invisible. But its gravitational influence
  on its surroundings can still be detected the
  stars surrounding the hole must move fast (due to
  Keplers and Newtons laws).

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Sleeping Monsters

• Theres even a 2,000,000 M? black hole at the
  center of the Milky Way. We can measure its mass
  by the motions of stars which pass close to it.

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AGN and Starbursts

• In the present day universe, AGN are rare.
  However, they are more common in interacting
  galaxies. This suggests that the orbits of some
  stars have been perturbed enough to pass close to
  the black hole. It also suggests that all
  galaxies possess supermassive black holes.

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AGN and the Universe

• Since quasars can be seen 90 of the way across
  the universe, they allow us to detect gas
  throughout the universe. We can therefore
  examine galaxies (and proto-galaxies) that we
  cant even see!

Any time the light from a quasar goes through a
galaxy that has hydrogen gas, there will be
absorption at the wavelength appropriate to
hydrogen. But remember this hydrogen is
moving, due to the Hubble Law. So
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AGN and the Universe

• Each absorption is due to hydrogen gas at a
  different redshift (i.e., distance). Quasars
  allow us to probe structure throughout the
  universe!

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Next time -- REVIEW