Other galaxies

1
Other galaxies

• Stars rarely collide
• But galaxies do
• (observations !)

2
Other Galaxies

• galaxy mergers

(computer simulation !)
3
Other galaxies

• Do other galaxies also contain supermassive black
  holes ? YES !
  
• Similar to accretion
• disk-jet connection in
• young stellar objects

4
Going to larger scales

• Many galaxies are in clusters (group small
  cluster)
  
• Local group
• - small cluster containing the
  milky way
  
• - about 20 galaxies within a
  cubic parsec
  
• - 3 spirals Milky Way,
  Andromeda (M31),
  
• M33
• - 4 irregulars MW-satellites
  Small and Large
  
• 
  Magellanic Clouds
  
• - several dwarf ellipticals
• Virgo Cluster - nearest rich cluster
• - about 2500 galaxies
• - distance about 15
  Mpc
  

5
Virgo Cluster
6
Midterm exam
astrophysics

• date May 11, 2005, 815 a.m.
• location Conrad Naber Hall
• bring pocket calculator
• NO text books, notes laptops etc.
• do NOT bring your own paper
• write on exam sheets directly

Spacephysics see web site
7
Cosmology

• Ancient Mythology and Modern Cosmology
• Is there a/Where is the difference ?

8
Example of a creation StoryThe Christian/Jewish
View

• Genesis In the beginning God created the
  heavens and the earth. And the earth was waste
  and void and darkness was upon the face of the
  deep

9
Common Concepts

• Action of a supreme craftsman
• Generation from a seedling/egg
• Imposition of order over chaos
• Life cycle dominates over eternal/unchanging
  there is a beginning
  
• Hybrid schemes act of creation, but supreme
  being/chaos existed forever

10
Scientific Creation Story 2005

• In the beginning there was neither space nor
  time as we know them, but a shifting foam of
  strings and loops, as small as anything can be.
  Within the foam, all of space, time and energy
  mingled in a grand unification. But the foam
  expanded and cooled. And then there was gravity,
  and space and time, and a universe formed.
• ? Is there a difference ?

11
The Scientific Method
specific instances
12
Sir Isaac Newton(1643-1727)Cosmology as a
Science

• Mathematical description
• of the Universe
• The same physical laws
• apply to earth and Universe

13
Newton Fundamental contributions

• Mathematics - series expansions
• - differential calculus
• - approximation methods
• -
• Optics - spectral analysis of white
  light
  
• Physics - Principia mathematica
• Astronomy - derive Keplers laws from
• gravitational forces
• ..

14
A toy universe

• According to Newton, what is going to happen ?
• The model Universe is going to collapse under its
  own gravity
  

15
Newtons Conclusion

• In order to avoid collapse
• homogeneous
• isotropic
• infinite size
• no center
• infinite in time
• has always been
• will always be
• ? perfect cosmological principle

16
The perfect cosmological principle

• homogeneous the universe looks the same
• everywhere on large
  scales ? there is no special place
  (center)
  
• isotropic the universe looks the same in all
• directions on the sky
  ? there is no special direction (axis)
  
• unchanging The universe looks the same at
• all times
  ? there is no special epoch

17
Olbers Paradox

• If the universe is i) eternal
• ii) (more or less)
  uniformly filled
  
• with stars
• iii) infinite
• then there is a star along each line of sight
• so Why is the night sky dark ?

18
Problems with an infinite universe

• Olbers Paradox Why is the night sky dark?

19
Olbers Paradox
Each shell contributes L1 4? ? r12?x l

infinite number of shells ? infinite luminosity

(at least) one of the assumptions must be wrong !
20
How to solve Olbers paradox ?

• Universe is finite
• Universe has finite age
• The distribution of stars throughout space is not
  uniform
  
• The wavelength of radiation increases with time
• Note for the big bang model, all these
  conditions are satisfied
  

21
Einstein

• speed of light const
• relativity of
• simultaneity,
• special relativity
• general relativity
• space-time is curved
• prediction of black holes
• prediction of gravitational waves

22
Einstein

• Universe has to be static!
• only possible if extra-term is included in
• equations to counter-balance attraction
• cosmological constant
• Einsteins biggest blunder

23
Edwin Hubble (1889-1953)

• Four major accomplishments
• in extragalactic astronomy
• The establishment of the Hubble classification
  scheme of galaxies
  
• The convincing proof that galaxies are island
  universes
  
• The distribution of galaxies in space
• The discovery that the universe is expanding

24
Doppler effect (for light)

• The light of an approaching source is shifted
  to the blue, the light of a receding source is
  shifted to the red
  

25
Doppler effect
The light of an approaching source is shifted to
the blue, the light of a receding source is shif
ted to the red.
red shift
blue shift
26
Doppler effect
redshift z0 not moving z2 v0.8c z?
vc
27
The redshift-distance relation
28
Key results

• Most galaxies are moving away from us
• The recession speed v is larger for more distant
  galaxies. The relation between recess velocity v
  and distance d fulfills a linear relation
  v H0 ? d
• Hubbles measurement of the constant H0
  H0 500 km/s/Mpc
  
• todays best fit value of the constant
  H0 71 km/s/Mpc (WMAP)
  

29
Question
If all galaxies are moving away from us,
does this imply that we are at the center?
Answer
Not necessarily, it also can indicate that the
universe is expanding and that we are at no
special place.
30
Einsteins General Relativity
observation of expanding Universe
Universe started from a point

Big Bang Model
31
Big Bang Model
32
Big Bang in a nutshell
33
Cosmological redshift

• While a photon travels from a distant source to
  an observer on Earth, the Universe expands in
  size from Rthen to Rnow.
  
• Not only the Universe itself expands, but also
  the wavelength of the photon ?.

34
Cosmological redshift

• General definition of redshift? for
  cosmological redshift

35
A large redshift z implies ...

• The spectrum is strongly shifted toward red or
  even infrared colors
  
• The object is very far away
• We see the object at an epoch when the universe
  was much younger than the present day universe
  
• most distant astrophysical object discovered so
  far z5.8
  
• z5.8 dark ages

36
Are there any indications that this picture is
correct?

• Yes !
• Primordial Nucleosynthesis
• Cosmic Microwave background

37
Primordial Nucleosynthesis
Georgy Gamov (1904-1968)

• If the universe is expanding, then there has
  been a big bang
  
• Therefore, the early universe must have been
  very dense and hot
  
• Optimum environment to breed the elements by
  nuclear fusion (Alpher, Bethe Gamow, 1948)
  
• success predicted that helium abundance is 25
• failure could not reproduce elements more
  massive than lithium and beryllium (? formed in
  stars)

38
The Cosmic Microwave Background (CMB)
Last scattering surface
transparent
opaque
39
Penzias and Wilson 1965

• Working at Bell labs
• Used a satellite dish to measure radio emission
  of the Milky Way
  
• They found some extra noise in the receiver, but
  couldnt explain it? discovery of the background
  radiation
  
• Most significant cosmological observation since
  Hubble
  
• Nobel prize for physics 1978

40
The cosmic microwave background radiation (CMB)

• Temperature of 2.7280.004 K
• isotropic to 1 part in 100 000
• perfect black body
• 1990ies CMB is one of the major tools to study
  cosmology
  
• Note 1 of the noise in your TV is from the big
  bang

41
More results from the CMB

• The Earth is moving with respect to the CMB ?
  Doppler shift
  
• The emission of the Galaxy
• Fluctuations in the CMB

42
Fluctuations in CMB responsible for structure
formation in the universe
43
Cosmic Structure formation
44
New developments
Science discovery of the year 1998
q0 0
q0 0.5
Data indicates q0 ting
fainter
more distant
45
From Supernova observations

• The expansion of the universe is accelerating
  !!!
  
• But gravity is always attractive, so it only can
  decelerate
  
• Revival of the cosmological constant ?

46
The fate of the Universe for ?0
k1
?0
?0
47
Wilkinson Microwave Anisotropy Probe (WMAP) (2003)
COBE (1992) WMAP (2003)
48
Summary of most important results of
WMAP

• Age of the Universe 13.7 billion years
• First stars 200 million years
• after Big
  Bang
  
• CMB decoupled 379 000
  years
  
• after Big
  Bang
  
• Hubble constant H0 71 (km/s)/Mpc
• Content of the Universe
• - 4
  Atoms
  
• - 23
  cold, dark matter
  
• - 73
  Dark Energy