1. Astrophysics and Cosmology
Lecture #26
11/19/2018
Lecture XXVI

2. Concepts Parsec, light year Curved space Hubble’s law Big Bang
Early universe
11/19/2018
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
11/19/2018
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
11/19/2018
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
11/19/2018
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:
Hubble telescope:
11/19/2018
Lecture XXVI

7. Hubble deep field
11/19/2018
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:
11/19/2018
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)
11/19/2018
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
11/19/2018
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
11/19/2018
Lecture XXVI

12. Expanding universe v=Hd The universe is expanding.
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.
11/19/2018
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
11/19/2018
Lecture XXVI

14. Universe evolution Age of the universe 1010 years
Cosmic Microwave background – echo of the Big Bang
11/19/2018
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)
11/19/2018
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
11/19/2018
Lecture XXVI

17. WMAP Launched from cape Canaveral on June 30 2001
11/19/2018
Lecture XXVI

18. Trajectory Lunar swingby Phasing loops
WE ARE LIKE OUR OWN LITTLE PLANET… WE ORBIT THE SUN.
Official arrival date: Oct 1, 2001
100 days to L2, 1.5e6 km from Earth.
11/19/2018
Lecture XXVI

19. COBE 1992
Bennett et al 2003
WMAP 2003
11/19/2018
Lecture XXVI

20. Facts first, then the conclusions!
11/19/2018
Lecture XXVI

21. BEYOND LCDM model FLATNESS + HST meas. of Ho (Spergel et al 2003)
Riess et al. 2001
+ HST meas. of Ho
de Bernardis et al 2000
Verde et al 2002
(Spergel et al 2003)
11/19/2018
Lecture XXVI
After

22. We (and all of chemistry) are a small minority in the Universe.
Compare gravitational rotation of galaxies with luminous matter
11/19/2018
Lecture XXVI