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Theres something strange at the center of our galaxy

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Even better correlation with stellar velocity in bulge... Correlation with the mass of the galactic bulge. Supermassive Black Holes ... – PowerPoint PPT presentation

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Title: Theres something strange at the center of our galaxy


1
Theres something strange at the center of our
galaxy
  • Modern large telescopes can track individual
    stars at Galactic Center
  • Need infra-red (to penetrate dust?)
  • Need very good resolution.
  • We have been observing for past 10 years

2
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3
  • The central object is
  • Very dark
  • Very massive (3 million solar masses)
  • Must be very compact (Star S2 gets within 125 AU
    of the center)
  • Currently the best case for any supermassive
    black hole

4
Why are Supermassive Black Holes always found in
Galactic Cores?
  • Gravity separates matter by density
  • The dense element iron sinks to Earths core
  • Heavy elements sink to centers of stars
  • Binary stars and massive stars sink to the center
    of star clusters
  • Supermassive black holes sink to the centers of
    galaxies
  • Massive galaxies sink to the center of galaxy
    clusters
  • This is a very general property of nature!

5
Is there a Supermassive Black Hole in Every
Galaxy?
  • Supermassive Black holes exist in centers of some
    galaxies
  • But how widespread are they? Does every galaxy
    have one?
  • Several teams set out to answer that question
  • Use best resources (HST, large telescopes on
    ground etc.) to gather lots of data on many
    nearby galaxies.
  • Systematic search for black holes
  • They found them everywhere they looked, and
    discovered interesting patterns
  • Correlation between size of black hole and the
    brightness of the galaxys bulge (but not the
    galactic disk)

6
Patterns Galaxies and their Supermassive Black
Holes
  • Even better correlation with stellar velocity in
    bulge

Correlation with the mass of the galactic bulge.
7
Supermassive Black Holes
  • Correlations between Supermassive Black Holes and
    their host galaxies are crucially important!
  • Argues for a connection between the formation of
    the galaxy and the supermassive black hole.
  • The details are still not well understood - an
    active area of current research!

8
Active Galactic Nuclei(When good black holes go
bad!)
  • Active Galactic Nuclear - AGN
  • Discovery of AGN (3C273)
  • What are AGN?
  • Radio-galaxies
  • AGN and colliding galaxies

9
I The discovery of AGN
  • Early 1960s
  • Radio astronomers started to survey the sky
  • Found many mysterious radio sources
  • Quasi-stellar radio sources (quasars for short)
  • Very difficult to identify radio images were too
    fuzzy to allow quasars to be localized on sky
  • Cyril Hazard
  • Used Lunar occultation to localize 3C273
  • I.e., measure the precise time when the radio
    signal from the quasar is blocked by the Moon
  • then use knowledge of the Moons position to
    determine position of quasar.
  • Hazard could localize 3C273 to about 1 arcsec.

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11
3C273
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13
Quasars are Bright and Far Away
  • M.Schmidt
  • Took Hazards position and observed it with
    normal (optical) telescope in particular, he
    measured its spectrum
  • Spectrum showed huge velocity, 50,000km/s
  • Hubbles law ? huge distance (700Mpc)
  • Thus, 3C273 must be very powerful to still appear
    bright when its so far away!
  • About 1000x luminosity of our whole galaxy
  • Source was variable ? must be small, about size
    of our solar system (Why?)

14
Rapid Time Variation means Small Source Size
  • What if the Sun stopped shining right now
    (instantaneously) - what would we see?
  • Nothing unusual for 8 minutes!
  • Then the center of the Sun would go dark -
    theres a little dark spot on the Sun today.
  • The dark circle would expand toward the bright
    edge of the Sun and, 2 seconds later, all would
    be dark
  • The 2 second delay happens because the center of
    the Sun is closer to us than the edges by about 2
    light seconds.
  • The fastest change that we could see happening
    to the entire Sun would take 2 seconds - this
    limit is set by the objects size

15
There are now many many examples of AGN
MCG-6-30-15
16
II The Theory of AGN
  • What powers AGN?
  • Define efficiency of an AGN
  • Think about efficiency of different processes
  • Chemical burning, ??10-9
  • Nuclear fusion, ??0.007
  • Accretion onto a black hole, ??0.1
  • Matter/anti-matter annihilation, ?1

17
How to Power AGN
  • Suppose AGN has power of 1040W and lasts for 10
    million years
  • Then, what masses are needed?
  • Chemical burning 2?1012 Msun
  • Nuclear burning 2?109 Msun
  • Accretion 2?108 Msun
  • Matter/anti-matter 2?107 Msun
  • Masses tend to argue for accretion (there are not
    large amounts of anti-matter in space!). And we
    know that billion solar mass black holes exist.

18
  • Now believe that AGN are indeed accreting
    supermassive black holes
  • Matter cant fall straight in forms an accretion
    disk. Accretion disks power jets.

19
III Radio galaxies
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Jets from Black Holes form Radio Galaxies
  • About 1-10 of AGN are radio-galaxies
  • Radio galaxies
  • Possess huge jets that transport energy away from
    center and entirely out of the galaxy
  • Processes associated with jets then give powerful
    radio emission
  • Material in the jets is moving very close to the
    speed of light how do we know this?

22
Faster than a speeding light ray?
  • Superluminal motion
  • Jets have blobs
  • Some blobs appear to move faster than light!
  • Motion faster than light is not allowed by the
    Special Theory of Relativity
  • Whats going on?
  • Superluminal motion is an optical illusion
    blobs partially catch-up with the light they
    emit.
  • But needs jet to be traveling close to the speed
    of light
  • No Warp-Drive yet.

23
Wormholes and Timewarps?
  • Wormholes
  • Wormholes may exist inside black holes
  • Build a stable wormhole and bring wealth and
    prosperity to your planet!
  • Timewarps
  • The idea of cause and effect
  • The assumption of causality and the speed of
    light
  • Can time-machines exist?

24
Astrophysicists view of black holes stops at the
event horizon
25
But there is structure inside the event horizon!
  • Nothing escapes from inside the Event Horizon

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27
Non-rotating Black Holes The Schwarzschild
Solution
  • Schwarzschild solution
  • Mathematical description of a non-rotating black
    hole
  • Discovered by Karl Schwarschild in 1916
  • Any normal particles/light entering event horizon
    are doomed to hit the singularity at the center
    of the black hole
  • Once there they will be totally destroyed
  • But, the Schwarzschild solution has an
    interesting mathematical structure
  • Suggests that particles traveling faster than
    speed of light can avoid the center
  • Then pass through a wormhole and emerge from a
    white hole into a new region of normal space

28
(Black Hole) Stuff goes in here
Avoids the Singularity of death
and comes out here! (White Hole)
29
Do Schwarzschild Black Holes Really Exist?
  • Probably not
  • Real stars do not form Schwarzschild black holes
    because they rotate!
  • Full Schwarzschild solution needs existence of
    white hole these violate key laws of physics
    (2nd law of thermodynamics).
  • Even if they did exist, they are unstable! Try
    to pass through it and it collapses!
  • An unstable wormhole wont bring prosperity to
    your planet.

30
Rotating Black Holes The Kerr solution
  • Kerr solution
  • Mathematical solution describing rotating black
    holes
  • Applicable to most real black holes in nature
  • Discovered by Roy Kerr in 1960s
  • More interesting than Schwarschild solution
  • This time, dont need to travel faster than light
    to avoid the singularity!
  • Singularity has a ring structure enter the
    wormhole by flying through the ring
  • Are then propelled from a white hole and emerge
    into another region of normal space.

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32
Can Wormholes form in Rotating Black Holes?
  • Again, seems unlikely
  • White holes still violate physical laws
  • Wormhole are still unstable
  • Some researchers think that there is not a hole
    in the ring through which to pass
  • Never trust a stranger selling low-mileage
    wormholes, although

33
There is one in New York (if you know where to
look)!
Scientific American, Jan 2000
34
Scientific American, Jan 2000
35
Alright, then lets build a Time Machine instead
  • Idea of cause and effect
  • Foundation of scientific reasoning
  • If one event can have an effect on the other
    event, they are said to be causally-connected.
  • To have any meaning, the cause must happen before
    the effect!
  • This requirement is called causality.
  • Einsteins theory of special relativity
  • What if a signal could be transmitted faster than
    light speed?
  • Then Einsteins Special Theory of Relativity
    shows that you can change the order of
    causally-connected events.
  • Can make effect happen before cause!
  • This seems to make no sense. We disallow this!
  • Causality seems to imply that no signal can
    travel faster than light

36
Is my Time Machine ready yet?
  • The big question Does Einsteins theory
    necessarily demand causality? Must Cause always
    precede Effect?
  • Surprisingly, and in contrast to everyday
    experience, this is not at all obvious!
  • To determine if Time Machines are possible, we
    probably have to understand the nature of
    space-time a lot better than we currently do.
  • Extra Credit Project Invent a Time Machine (0.5
    points - due tomorrow).
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