Science project

1. 3/14/2023 Lecture XXVI 1
Lecture #26
Astrophysics and Cosmology

2. 3/14/2023 Lecture XXVI 2
Concepts
• Parsec, light year
• Curved space
• Hubble’s law
• Big Bang
• Early universe

3. 3/14/2023 Lecture XXVI 3
Units to measure large distances
• Light second = cx1s=3x108 m = 3x105 km
• Earth circumference = 40,000 km = 0.13 light seconds
• Earth – Moon = 1.28 light seconds
• Light minute = cx60s=1.8x1010 m
• Earth – Sun = 8.3 light minutes
• Earth – Pluto = 311 light minutes
• Light year = cx1y=9.46x1015 m

4. 3/14/2023 Lecture XXVI 4
Scales of the universe
Distance from Earth
• Proxima Centauri (next door neighbor) – 4.3 ly
• Center of our Galaxy (Milky Way) 3x104 ly
• Our galaxy (Milky Way) is a disk
• D=100,000 ly
thickness 2,000ly
total number of stars in Milky Way ~1011
• Nearest galaxy (Andromeda nebula) 2x106 ly
• Farthest galaxies 1010 ly

5. 3/14/2023 Lecture XXVI 5
How to measure heavenly distances?
Cannot clock the light, cannot use a ruler…
Parallax – apparent motion of a star against the
background of more distant stars
f=90-q
D=d/tan(f)
d=1.5x108km
Parallax angle in seconds
– distance to the star in
Parsec = 3.26 ly
q
f
d
D

6. 3/14/2023 Lecture XXVI 6
Other information from the sky
• Apparent brightness  on average related to distances
• Spectrum  temperature
– Red shift – related to relative velocity  distances
• High energy radiation
• Neutrinos (m=~0, weak interaction) – propagate great
distances
• Experiment  observation
• SLOAN digital sky survey: http://skyserver.fnal.gov/en/
• Hubble telescope:
http://www.stsci.edu/ftp/science/hdf/hdf.html

7. 3/14/2023 Lecture XXVI 7
Hubble deep field

8. 3/14/2023 Lecture XXVI 8
Hertzsprung-Russel (H-R)
diagram
• Luminosity increases with
star’s mass
• Temperature related to the
wavelength lT=2.9x10-3mK
• By measuring l we can find T,
then using H-R diagram we
can predict the absolute
brightness (L).
• The apparent brightness (l) is
related to L and the distance
to the star:
2
4 d
L
l

=

9. 3/14/2023 Lecture XXVI 9
Evolution of the stars-I
• Stars are born when gaseous clouds (mostly hydrogen) contract
due to gravity
• Gravity accelerates the particles of the star inward  kinetic
energy is increasing, could be large enough (1keV~107K) to
overcome coulomb repulsion and start nuclear fusion HHe (In
our Sun – yellow dwarf)
• Pressure from the energy released in fusion keeps the star from
collapsing
• When the hydrogen in the core burns out the core contracts and T
goes up  the outer envelope expands and cools down (Red giant)
• The core continues to heat up and He starts burning in fusion and
continue to higher Z’s ending nucleosynthesis at Fe and Ni
• No pressure from fusion – gravitational collapse – white dwarf
• Pauli principle for orbital e keeps the star from further collapse
• T goes down white draft becomes black dwarf (cloud of ash)

10. 3/14/2023 Lecture XXVI 10
Evolution of the stars-II
• Heavier stars continue to burn beyond Fe and Ni in
endoergic reactions
• In addition the following process can occur
e-+pn+n
Neutrons are formed in abundance – neutron star (>~1.5
mass of Sun, D~10km) Pauli principle for neutrons limit
the size
No electrostatic repulsion – leads to a catastrophic collapse
– supernova explosion
If mass of neutron star >2-3xSolar mass – black hole – not
even light can escape

11. 3/14/2023 Lecture XXVI 11
Gravity and curvature of space
• Einstein’s general relativity: No observer can determine
by experiment if he is accelerating or is rather in a
gravitational field
• Explain gravity (interaction) through curvature of space
(geometry)
• Establish equivalence between gravitational and inertial
mass
• Experimental proof: Curving light: straight line
becomes curved in gravitational field
• Extreme curvature – black hole: black because not even
light can escape it

12. 3/14/2023 Lecture XXVI 12
Expanding universe
• Redshift – spectral lines shifted – object is moving
• In 1929 Edwin Hubble, measured the redshifts of a
number of distant galaxies. the redshift of distant
galaxies increased as a linear function of their distance
• Hubble’s law
v=Hd
• v- velocity of galaxies, d – distance
• H=80km/s/Mpc
• The universe is expanding.

13. 3/14/2023 Lecture XXVI 13
Age of the universe
v=Hd
• v- velocity of galaxies, d – distance
• H=80km/s/Mpc = 20km/s/million ly
• Farthest galaxy 1010ly
• t=d/v=d/(dH)=1/H=15x109yr

14. 3/14/2023 Lecture XXVI 14
Universe evolution
eV
eV
J
K
K
J
kT
KE 4
19
23
10
6
.
2
/
10
6
.
1
3
/
10
4
.
1 -
-
-

=



=
=
Age of the universe 1010 years
Cosmic Microwave background – echo of the Big Bang

15. 3/14/2023 Lecture XXVI 15
Cosmic microwave background
• Discovered in 1964 by Arno Penzias and Robert Wilson
as a “noise” in radio telescope
• Cosmic microwave background at l=7.35 cm
• Blackbody radiation at T=~3K
• Present precise measurement 2.7K
• Echo of the Big Bang, predicted in 1940 by George
Gamow
• Radiation “decoupled” from matter when atoms were
formed and there were no free electrons to scatter light
(~3000K, 0.3 Myears after birth)

16. 3/14/2023 Lecture XXVI 16
Fate of the Universe
• Gravity slows down the expansion
• Depending on the density the universe might
– Continue to expand infinitely
– Collapse back to a point

17. 3/14/2023 Lecture XXVI 17
WMAP Launched from cape Canaveral on June 30 2001

18. 3/14/2023 Lecture XXVI 18
Trajectory
100 days to L2, 1.5e6 km from Earth.
Lunar swingby
Phasing loops
Official arrival date:
Oct 1, 2001

19. 3/14/2023 Lecture XXVI 19
Bennett et al 2003
COBE 1992
WMAP 2003

20. 3/14/2023 Lecture XXVI 20
Facts first, then the conclusions!

21. 3/14/2023 Lecture XXVI 21
BEYOND LCDM model FLATNESS
de Bernardis et al 2000
(Spergel et al 2003)
Riess et al. 2001
02
.
0
02
.
1 
=

Verde et al 2002
After
+ HST meas. of Ho

22. 3/14/2023 Lecture XXVI 22
We (and all of chemistry) are a
small minority in the Universe.
Compare gravitational rotation of galaxies with luminous matter