Industrial Strength Cosmology

1
This page is intentionally blank
2
(No Transcript)
3
A new view of the Universe VI Fred WatsonApril
2005
Industrial-Strength
Cosmology
4
Industrial-Strength Cosmology
5
(No Transcript)
6
COSMOLOGY The study of the origin and evolution
of the Universe as a whole
7
Three microbes in Edinburgh
One will see what one can do
What we need is more money for cosmology
8
Professor Malcolm Longair We are witnessing the
dawn of a new realm of precision
cosmology August 2000

• Better described as industrial-strength
  cosmology because it is very robust
• The robustness comes from advances in
  astronomical technology and theoretical physics
  in recent years

9
Two kinds of observational cosmology

• Near-field cosmology
• History of nearby objects, e.g. stars, galaxies
• Far-field cosmology
• Studies of the most distant objects galaxies,
  quasars, gamma-ray bursters etc.
• Studies of gravitational lensing, the cosmic
  microwave background, etc.
• Both kinds tell us about the evolution of the
  Universe

10
The Nearby Universe
Industrial-Strength Cosmology
11
Tools of the trade
Astronomers dont use light years. (You cant
measure a light year.) Astronomers use
parsecs. (Not to be confused with parsnips.)
12
Whats a parsec?
Earth
1 arcsecond
Sun
Star appears to move against background
Earth 6 months later
1 parsec 3.27 light-years
13
Galaxies

• Basic building-blocks of the Universe

• Around 100,000,000,000 stars
• Lots of gas and dust (in spirals)
• Around 100,000 l.y. across (or 30 kiloparsecs)

14
Edge-on view of a spiral galaxy
The gungy brown stuff is dust, which limits the
view from the inside
15
In galaxies, stars are born
The Eagle Nebulastellar birthplace
16
The Vela supernova remnant
and die
17
The Expanding Universe
Industrial-Strength Cosmology
18
But how do we know its expanding?
The Hubble Deep Fielda core-sample of the
Universe
Most of these galaxies have look-back times
measured in billions of years
Industrial-Strength Cosmology
19
Tools of the trade
Telescopes can be used as celestial speedometers
for galaxies. Astronomers record and measure the
spectra of the galaxies.
20
(No Transcript)
21
(Not to be confused with a plectrum)
22
Spectra of about 100 galaxies arranged in order
of increasing velocity
Blue end
Red end

23
Hubbles Law (1929)

• The speed of recession of a galaxy, v, is
  proportional to its distance, d, from the
  observer.
• v H0 d
• The constant of proportionality, H0 is called the
  Hubble constant, and is in units of km/s per
  megaparsec. (1 Mpc 3.27 million l.y.)
• Accepted value today is H0 ? 75 km/s/Mpc.

24
But what does redshift mean?
Z

• We now know the Hubble law comes about because
  space itself is expanding, stretching the
  wavelength of light moving through it.
• Rather than calculating a galaxys velocity,
  astronomers simply measure the fractional shift
  of its spectrum towards the red resulting from
  the expansion (?? / ?emitted).
• This is called the redshift, z

25
Tools of the trade
The Really Useful Quantity 1/(1 z) tells us
how big the Universe was when the light was
emitted. Remitted / Rnow 1/(1 z) E.g.,
for a galaxy with z 1, the Universe was half
its present size when it emitted its light.
26
An Einstein Ring (B0047-2808)

• zforeground 0.485 zbackground 3.595

27
The Age of the Universe
Industrial-Strength Cosmology
28
How old is the Universe?

• In 1927, Georges Lemaître realised that Hubbles
  Law means the Universe itself is expanding.
• He extrapolated back in time to when all the
  galaxies were at a single point.
• The age of the Universe is then given by the
  Hubble time 1/H0
• If H0 75 km/s/Mpc, the Hubble time is 13
  billion years.

29
Lemaîtres Picture
Defining quantity Hubble constant, H0 (uniform
expansion) Problem it only works if the Universe
is completely empty.
30
Refined Model (1970s)
Defining quantities Hubble constant, H0
(current expansion) cosmic density parameter,
? Problem the Universe is younger than most of
its contents.
31
Dark matter and the composition of the Universe
32
Current Model
Defining quantities Hubble constant, H0
(current expansion) cosmic density of all
matter, ?m cosmic density of ordinary matter,
?b dark energy (cosmological constant,
?) (evidence from distant supernovae, etc.)
33
Age of the Universe
34
Mapping the Universe
Industrial-Strength Cosmology
35
Industrial-Strength Cosmology
36
Survey Regions

• Pie-slice directions in the 2dF Galaxy Redshift
  Survey

37
The distribution of galaxies allows us to
measure theclumpiness of the Universe
38
Then, of course, there are the quasars
Spectra of 11,000 quasars from the 2dF
survey arranged in order of distance
39
Quasars are also clumpy.
The biggest survey to datebut it still shows us
only 0.1 of the Universe
40
The hot Big Bang
Industrial-Strength Cosmology
41
The Hot Big Bang model

• Modern equivalent of Lemaîtres picture.
• It postulates a hot Big Banga unique event in
  which not only the matter in the Universe was
  created, but space and time as well
• Three vital pieces of evidence support it
• the expansion of the Universe
• the relative abundances of light elements
• the cosmic microwave background radiation.

42
Whats the cosmic microwave background radiation?

• Faint background glow in the millimetre
  wavelength region of the radio spectrum.
• Almost perfectly uniform in all directions.
• It is the echo of the Big Bang fireball itself.
• Were seeing back in time to a moment 300,000
  years after the Big Bang when the Universe ceased
  to glow with brilliant white light and became
  transparent

43
R 330 metres after 1 second
R 660 metres after 2 seconds, etc.
i.e., R increases at the speed of sound.
44
Cosmic microwave background radiation

• Why dont we see a brilliant white back-ground in
  every direction?
• The radiation has been redshifted by the
  expansion of the Universe.
• The light waves have been s-t-r-e-t-c-h-e-d by
  about 1000 times to become longer wave- length
  microwaves. Thus, zCMBR ? 1000.
• The CMBR is easily the most ancient fossil
  remnant we can see

45
COBE all-sky map showing 1-in-105 temperature
fluctuations
The hot-spots are the seeds of the structure we
see in the Universe today
46
What does the CMBR tell us about the Big Bang?

• The rippling in the CMBR (due to acoustic
  oscillations in the fireball) closely matches the
  clumpiness seen in the redshift surveys. It is
  the baby face of todays Universe
• The radiation is very smoothfluctuations in the
  early fireball must have been ironed out by an
  exceedingly short period of inflation.
• The rippling can tell us much, much more about
  both the Big Bang and the evolution of the
  Universehence NASAs WMAP

47
Wilkinson Microwave Anisotropy Probe
Launched 30.6.2001
Industrial-Strength Cosmology
48
In summary
But wait!
Not such a bad effort for a bunch of microbes
There's more!
49
Industrial-Strength Cosmology
50
Theres nothing wrong with a Dish as long as
its not lamb casserole
51
The End
Industrial-Strength Cosmology