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C O U R S E 
Galaxies and Cosmology
S. George Djorgovski, Caltech
C O U R S E   L E C T U R E 
20th Century Developments in Cosmology
Notes taken on July 11, 2015 by Edward Tanguay
dark matter
Fritz Zwicky (1898–1974)
realized that the mass of the Coma Cluster was 400 times the amount of mass in its visible stars
Sinclair Smith
Virgo Cluster
other astronomers did not take these statements too seriously since there was no other evidence for them
1970s is was accepts when more evidence was found
from flat galaxy rotation curves
dark matter now plays a key role in models of structure formation
early galaxy evolution
Edwin Hubble (1889-1953)
designed a set of cosmological tests to determine the geometry of the universe
Hubble diagram
the plot of distance related to velocities of galaxies
as you go further into space, the line deviates from straight
Allan Sandage (1926-2010)
determined the first reasonably accurate values for the Hubble constant and the age of the universe
discovered the first quasar
used brightest galaxies as "standard candles"
assuming these were constant
this failed
because they are not constants
they evolve
stars evolve
galaxies merge
so until the mid 1990s, the Hubble diagram was not considered a serious test
Big Bang Theory
Ralph Alpher
George Gamow
Robert Herman
predicted the afterglow of the original hot stage of the universe would be present in the universe as a thermal background
predicted the abundance of very light elements
helium, second lightest element
24% of the total elemental mass of the universe
discovery of powerful radio galaxies
after WWII thanks to the radars technology during the war
radio astronomy began
began mapping the sky with radar data
Walter Baade
Rudolph Minkowski
1943 discovery of the Active Galactic Nuclei
Carl Seyfert
observed bright nuclei in nearby spiral galaxies
1948 Steady State Cosmology
proposed by
Thomas gold
Hermann Bondi
Fred Hoyle
Hoyle did not agree with the Big Bang theory so it was a response to this
new matter is continuously created as the universe expands
it is now rejected by the vast majority of cosmologists, astrophysicists and astronomers, as the observational evidence points to a hot Big Bang cosmology with a finite age of the universe
1963 discovery of quasars
first quasars were discovered with radio telescopes in the late 1950s
many were recorded as radio sources with no corresponding visible object
quasi-stellar radio source
the most energetic and distant members of a class of objects called active galactic nuclei, or AGN (a compact region at the center of a galaxy that has a much higher than normal luminosity over some or all of the electromagnetic spectrum, the radiation from AGN is believed to be a result of accretion of mass by a supermassive black hole at the centre of its host galaxy)
the faster objects recede, the further away they are
Cyril Hazard
obtained precise measurements of stellar
Allan Sandage
Maarten Schmidt
1930s-1980s discovery of the Large Scale Structure
1930s Zwicky, Shapely began to map how galaxies clump together in space
clear that they were not randomly distributed
1950s-1980s measurements of redshifts
implied distances to vast number of galaxies
1950s promoted the idea that galactic clusters are grouped into superclusters
our immediate galactic neighborhood forms what he called a supercluster
was indication of structures that were larger than anything seen before
the Milky Way is in the Local Group of galaxies, which in turn is in the Laniakea Supercluster
the Virgo Supercluster is an appendage of the Laniakea Supercluster
1965 discovery of Cosmic Microwave Background
Arno Penzias
Robert Wilson
Nobel Prize, 1978
provided evidence for the Big Bang theory
today we can measure it with space instruments