Introduction Flashcards
Definition of cosmology ?
It is a branch of astronomy concerned with the study of the origin and evolution of the universe, from the Big Bang to today and into the future.
Which galaxy survey shows the cosmological redshift?
SDSS and 2MASS show that distant galaxies display redshifted spectra
Hubble law?
v ) H0*d
Ho = ?
70 km/s/Mpc
Latest Planck values indicate 67km/s/Mpc
SNe rather indicate 72km/s/Mpc
1 Mpc = ?
= 3 Myr = 3e22m = MW-M31
Density and temperature of the Universe today ?
Today, the density of the universe is 0.2atom/m3 and its temperature is approximately 2.7 K
Spectrum of the CMB?
BB spectrum to excellent level of accuracy
Fluctuation of the intensity of the CMB?
Detectable at a 10^-5 level
What does the BB spectrum of the CMB tells us?
It indicate that matter and radiation must have been in equilibrium at some stage of the cosmic history. But this equilibrium is currently nowhere to be must so it must have happened in the past.
What experiments study the CMB?
PLANCK, COBE and WMAP
How do we measure the temperature of the CMB in the past?
By a spectral analysis of absorption lines in the cold distant universe : the strenght of the lines depends on the intensity (and therefore temperature) of the CMB
What are the three observations that support the theory of an expending Universe ?
Cosmological redshift => distances are increasing through time
Atomic abundance => helium is produced by thermonuclear fusion. Such reaction only happens at very high temperatures and densities.. It happens in stars, but stars are not efficient enough to be held responsable for all the helium in the universe. There must have been a time when the universe was able to do thermonuclear fusion meaning, it much have hotter and denser in the past.
The CMB => its BB spectrum tells us that matter and radiation must have been at equilibrium in some stage of the cosmic history. Such equilibrium is only possible in a hotter environment.
Give the main epochs of the Universe’s history
Inflation (t~10^-35s)
Nucleosynthesis (t~3min)
Recombination (t~380 000 years)
Cosmic down (t~3Mrys) (following the Dark Ages)
Reionisation (t~1Gyr)
Today(t~13.8Gyrs) (following the beggining of the Dark Energy domination period around t~7Gyrs)
Hint that the Universe is more massive than it looks
The dynamic of matter inside galaxy clusters
Flat rotation curves of galaxies
Gravitational lenses
The properties of the CMB
The current expension of the Universe
In many contexts there seems to be a dark matter dominating the mass budget of the Universe.
What do DM models and simulations predict regarding galaxies?
Galaxies are expected to have universal DM profils and many substructures
It is difficult to reconcile with observation so far bc DM can only be inferred from observation and that the mapping from baryons to DM is hard to pin down.
How do we measure the expension history of the Universe?
By measuring the distance distribution of SNe
Concordance model states that
The energy budget of the Universe today is :
~5% baryons
~27% dark matter
~68% dark energy
What is the universal baryon fraction ?
fb = rhob / (rhob + rhoDM) ~0.15
Does the spatial distribution of matter in the Universe depends on the scale ?
On small scales (<100Mpc) it is scale free
On large scales (~120Mpc) it presents the inprint of cosmic sound waves called the Baryonic Acoustic Oscillations (BAO)
On very large scales (>1Gpc) it is scale free and possibly related to the inflationnary era
How do we get the spatial distribution of gas ?
We use the Lyman alpha forest technic. It consists in measuring absorption feature in distance lighthouse (such as quasars) spectra : each feature corresponds to a cloud along the line of sight.
Photon number density ?
400 photons/cm3
Energy density ?
corresponds to the mass energy of 5atoms/m3
Size of the observable universe?
14.5Gpc
