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Formation
of
Stars and Galaxies
Introduction
1.
Timeline and Big Bang
The Instruments
1.
Optical Telescopes
a) Use different regions of Electromagnetic Spectrum
i. Visible EM region
ii. Infrared EM region
iii.Ultraviolet EM region
b) Types
i. Refracting
ii. Reflecting
iii.Catadioptric
2. Radio Telescopes
3. X-Ray and Gamma-Ray Telescopes
The Objects
1. Stars
2. Nabula
3. Galaxies ( More than 100 billion )
i. Have 10 million to one trillion stars
ii. Most galaxies are 1,000 to 100,000 parsecs in
diameter and are usually separated by distances of the
order of millions of parsecs (mpc).
Types of Galaxy
i. Elliptic
ii. Spiral
iii. Barred-Spiral
iv. Irregular
M87
NGC4414
NGC1300
NGC1427A
Hubble’s Tuning Fork ….. more
4. Groups , Clusters and Superclusters
i. Group
A group of galaxies contain about < 50 galaxies,
a diameter of 1 to 2 megaparsecs, masses contained in
groups is typically ~ 1013 solar masses and the model
applied is CDM.
ii. Cluster
A cluster of galaxies contain 50 to 1000 galaxies, hot
X-ray emitting gas, clusters typically have masses from
1014 to 1015 solar masses and large amounts of dark
matter a diameter from 2 to 10 Mpc . A group is a
member of cluster
iii. Supercluster
A superstructure can have extents of order 100 Mpc,
have masses above 105 solar masses. A cluster is
member of supercluster
5. Filaments
of galaxies are 50 to 80 mpc in length
6. Black Holes and Supermassive Black Holes
i. If a collapsing star of over 3 solar masses does not
eject matter, it becomes a black hole.
ii. a mass of an order of magnitude between 105 and
1010 of solar masses. Most, if not all galaxies,
including the Milky Way, contain supermassive
black holes at their galactic centers.
7. Dark Matter and Dark Energy ….. more
8. Voids
A void billion light years across was found in 2007
9. Walls
i. Great Wall (cfA2) of galaxies, a very large
structure discovered in1989 is 500 million l years
long, 200 million l years wide and 15 million l years
thick.
ii. Sloan Great Wall of galaxies , the largest structure
discovered in 2003 is 1.37 billion light years but is not
a structure in the strict sense
Big Bang and Models of Cosmology
1. Lambda - CDM ( Cold Dark Matter )
It explains cosmic microwave background observations, as
well as large scale structure observations and supernova
observations of the accelerating expansion of the universe.
Cold Dark Matter is explained as being cold its velocity is
non-relativistic (v<<c) ,can not cool by radiating photons and
collisionless (i.e., the dark matter particles interact with each
other and other particles only through gravity).
2. WDM ( Warm Dark Matter )
Recently WDM predicted the Black Hole formation at the
centrer at the center of galaxy.
3. HDM (Hot Dark Matter)
It is represented primarily by neutrinos, does not apparently
account for the pattern of galaxies observed in the Universe.
Discovery of dim dwarf galaxies filling void negates HDM.
The two models CDM and WDM are still competing with each other and computer
simulations don’t discard them.
Galaxies Formation
1. Models and Computer Simulations
2. Primordial Fluctuations
Large clumps of gases and protogalaxies are
formed
3. Central Quiescent theory
Inside Dark Matter halos galaxies are formed by
slow accretion. Massive galaxies should be bright.
4. Collisional Starburst Scenario
Galaxies are formed quickly by collisions
between small clumps of matter , produces could
trigger a huge burst of star formation.
5. Supermassive Black Holes at the center
small "seed" black holes, which formed in the
very early universe, served as gravitational "roots"
for the clouds of gas around them
6. Top-Down Formation
7. Bottom-Up Formation
8. Formation of Spiral Galaxies
Lambda-CDM Model supports it. Slow star
formation
9. Formation of Elliptical Galaxies
Formed by merger of Galaxies and quick
star formation. Have supermassive black
holes at the centers.
10. Formation of Barred-Spiral Galaxies
possible cause of bar creation is tidal
disruptions between galaxies. The bar
structure decays over time
Star Formation
1. Accretion of gases and shrinkage under gravity at
1.
10 kelvin or less forms a protostar.
2. Shrinkage continues and temperature rises.
3. At few million kelvin therminuclear reactions of
hydrogen start. Protostars less than 0.08 solar
masses (0.08M) can never start thermonuclear
process.
4. Time of shrinkage and burning of hydrogen
depends on mass of protostar.
5. After hydrostatic and thermal equibrium star
becomes a stable star and occupies the main
sequence of H-R diagram. ……. Diagram
Nucleosynthesis of Stars
1. After consuming hydrogen if the star is less than
Chandrashekhar limit of 1.4Mass of the sun, it will become a
white dwarf having volume about earth
2. At 100 million kelvin at the core helium burning starts
producing carbon and oxygen.
3. At 600 million kelvin and mass equl to 4 M carbon burning
begins producing neon, oxygen and magnesium
4. At 1.2 billion kelvin neon burning begins
5. At 1.5 billion oxygen starts burning. Pricipal prouct is
sulpher , it also produces silicon, phosphorus and magnesium
6. At about 2.7 billion kelvin silicon burning starts it produces
iron and further burning stops. Any star with more than 10M
can develop iron core.
7. When density reaches more than 4x1017 kg/m3 a neutron star
is born. If mass >3.0M it will become a black hole.
8. For 25M carbon burns for 600 years, neon for 1 year, oxygen
for 6 months and silicon in 1 day.
END