This is a very broad overview of cosmology. It includes an introduction to galaxies, the large scale structure of the universe, black holes, and the fate of the universe. It is intended for teenagers and up.

1. To the Edge of Infinity
Anna M. Quider
Institute of Astronomy
University of Cambridge
14Sept 2010
7 July 2009

2. Today’s Talk
Primer on Gravity
then...
The development of structure in the universe
(from the Big Bang to present-day galaxies)

3. Gravity
Sir Isaac Newton
1643-1727

4. Gravity
Ma Mb
F
r
F = G x Ma x Mb
r2

5. Gravity

6. Gravity
Albert Einstein
1879-1955

7. Gravity

8. Gravity

9. Gravity

10. Black Holes
As far as we know, they only come from the death of a
very massive star
They range in size from stellar mass sized black holes to
supermassive black holes that are billions of times the mass
of the Sun
We think a supermassive black hole lives in the center of all
large galaxies
Can’t see black holes themselves--can only see their effects

11. Black Holes
Small black hole Large black hole
accreting matter from powering very
companion star energetic jets from a
(Cygnuis X) galaxy (quasar)

12. Small Black Holes
• Made by the death of a massive star (>20Msun)
• Resulting black hole will be at least ~3Msun (any smaller
and you’d get a neutron star or white dwarf rather
than a black hole) and no more than ~a few x 10Msun
(because the black hole must be considerably less
massive than the star that made it and the largest stars
are ~100Msun)

13. Supermassive Black Holes
• Made when a small black hole
consumes other black holes,
stars, and gas
• Can grow to billions of solar t
masses
• Live in center of galaxies
White circles are galaxies
Black dots are black holes

14. Supermassive Black Holes
Sagittarius A*:
Supermassive black hole in center of our galaxy

15. Supermassive Black Holes

16. Gravitational Waves
• Emitted when compact objects are in binary orbit
or merge together
• Orbiting objects slowly spiral in towards each

17. Gravitational Waves

18. LIGO
4 km
4 km
Ground-based laser interferometer

19. Gravity
What we need to know:
1. Gravity pulls objects together
2. The more matter an object has, the more
matter it can pull towards itself
3. The closer two objects are to each other, the
more gravitational attraction they feel
“The rich get richer and the poor get poorer”

20. In the beginning...
The Big Bang!

23. In the beginning...
...the universe was an expanding hot soup of particles...
...the universe cooled as it expanded...
Eventually Hydrogen and Helium atoms form and then
things get interesting for astronomers

24. First Light in Universe
About 400,000 years after the Big Bang
Fluctuations: one part per million

25. First Light in Universe
About 400,000 years after the Big Bang
Fluctuations: one part per million

26. First Light in Universe

27. Redshift
Means light looks more red to you (the observer) than it actually was when it
was emitted from the source
Different kinds:
1. Doppler: small scale redshifting and blueshifting of light because the
emitting object is moving away from you or towards you -- like hearing a siren
approach and pass you
2. Cosmological: Light gets stretched as it travels through the expanding
universe and this causes the light to appear more red when it reaches its
destination
3. Gravitational: It takes energy for light to climb out of a gravitational
potential well so the light appears more red (lower energy) when it finally
comes out of the gravitational field

28. Redshift
Doppler Redshift Cosmological Redshift

29. Early Galaxies
Hubble Deep Field (1995)

30. Early Galaxies
Hubble Deep Field (1995)

31. Early Galaxies
Hubble Deep Field
(1995)
about 3,000 objects
10 days of data with HST
Some galaxies from about
1 billion years after Big Bang

32. Early Galaxies

33. Early Galaxies
Hubble Ultra Deep Field (2003-04)
about 10,000 objects
11.3 days of data with HST
Some galaxies from about 800 million years after
Big Bang (though may have even younger objects,
too!)

35. Keeping Our Orientation

36. Early Galaxies
mages of 25 from about 3.3 ~ 2 in years after Big Bang
Galaxies galaxies at z billion the GOODS-N field, ea
Law et al. 2007b). Note the complex morphologies of

37. Gravitational Lensing
Gravity distorts and magnifies light from distant galaxies

38. Gravitational Lensing
distorts: stretched arcs and/or multiple images
magnifies: more light reaches the Earth

39. Early Galaxies
The Cosmic Eye
The 8 o’clock Arc
The Clone
The Cosmic Horseshoe

40. Keck Telescopes
Keck Telescopes
Hawaii, USA
10 meter mirror diameter

41. The Rest of the Galaxies
Sloan Digital Sky Survey
Surveying 1/4 of night sky
About 1 million galaxies analyzed

42. The Rest of the Galaxies

43. The Rest of the Galaxies
Galaxy Clusters
-Contain 1000s of galaxies
-Are the largest structures
held together by gravity
Perseus Cluster

44. Dark Matter
Only interacts through gravity
Does not interact with light
Normal matter follows the dark matter’s clumping

45. The Rest of the Galaxies

46. Dark Matter and a Cluster
Abell 2218

47. Dark Matter and a Cluster
Bullet Cluster
Blue = dark matter
Red = gas in cluster

48. Dark Matter and a Galaxy

49. Dark Matter Evidence
Spiral Galaxy Rotation Curves
Observed
Only luminous matter
(theoretically predicted)

50. Dark Matter Evidence
Spiral Galaxy Rotation Curves
Observed
Only luminous matter
(theoretically predicted) Curve for NGC3198

52. Different Galaxy Types
Spiral Galaxy

53. Spiral Galaxy Formation

54. Spiral Galaxy Formation

55. Spiral Galaxy Formation

56. Different Galaxy Types
Elliptical Galaxy

57. Different Galaxy Types

58. A Little Reminder...
Early galaxies don’t
look like the galaxies
we see in the
present-day universe!

59. Galaxy Mergers
z Age of Universe
7 0.75 Billion Years
2 3.3 Billion Years
1 6 Billion Years
0.5 8.6 Billion Years
0 Today

60. Galaxy Mergers
Antennae Galaxies

61. Galaxy Mergers
Our Local Group

62. Milkey Way’s Mergers

63. Andromeda, here we come!!!
(meet you in a few billion years!)

64. What is the fate of the universe?
Depends on density of universe
(which controls geometry of universe)
density of universe > critical density: Positive Curvature: Closed.
Volume is finite but unbounded.
density = crititcal density: Zero Curvature: Flat.Volume is infinite.
density < critical density: Negative Curvature: Open.Volume is infinite.

65. What is the fate of the universe?
Depends on density of universe
(which controls geometry of universe)

66. Dark energy could be
complicating the picture...
Latest evidence is that the
universe’s expansion is
accelerating due to some
unknown repulsive energy!
We call this repulsive energy
“Dark Energy” because we
have no idea what it is

67. Supernovae Type Ia
white dwarf
Type 1a Supernova large companion star
All Type 1a Supernovae have the same luminosity so
their apparent brightness is directly due to their
distance from us.

68. Supernovae Type Ia

69. Mass-Energy budget of Universe

70. Bringing it full circle
Gravity shapes the
structure of the universe

71. Bringing it full circle
Gravity shapes the
structure of the universe
Tiny variations in the very early
universe + gravity create the large-
scale structure of the universe

72. Bringing it full circle
Gravity shapes the
structure of the universe
Tiny variations in the very early
universe + gravity create the large-
scale structure of the universe
Gravitational lensing let’s us study
galaxies and dark matter in the universe

73. Bringing it full circle
Gravity shapes the
structure of the universe
Tiny variations in the very early
universe + gravity create the large-
scale structure of the universe
Gravitational lensing let’s us study
galaxies and dark matter in the universe
Galaxies have different types and
ages and they merge together