Cosmology Flashcards
What is the Doppler Effect
The apparent change in wavelength and frequency of a wave produced by a source as it moves towards or away from the observer
Explain the doppler effect
As the source moves towards the observer, the waves are compressed and the wavelength decreases.
As the source moves way from the observer, the waves spread out and the wavelength increases
What is Red-Shift
What is the formula?
The apparent decrease in frequency of a source of light as it moves away from an observer
Red Shift = Change in Frequency / Initial Frequency
Red Shift = Velocity of object/ Speed off light in a vacuum
Redshift = -Change in wavelength / Initial Wavelength
State Hubbles Law
The velocity of receding galaxies is proportional to their distance from earth
v= HD
State the standard units in the equation v= Hd
v = recession velocity km s^-1
d = Distance from Earth (Mega Parcsecs)
H = Km s^-1 Mpc^-1
What is a Quasar?
Most distant object in the universe, shown by a very larger redshift and a very high recession velocity
At the centre is a huge black hole, with an event horizon the size of a solar system. Surrounded by a disc of matter. As matter falls into the black hole, jets of radiation are emitted from the poles of the Quasar.
Appears very bright as swallows many stars
Emits radiation from the whole of the Em spectrum
What is the big Bang theory?
13.8 billion years ago all matter in the universe exploded from an extremely hot and dense point, and expansion is still ongoing
Explain CMBR
Explain its black body distribution
Cosmological Microwave Background Radiation
Heats signature left behind after the big bang
The Initial radiation in the big bang explosion has been shifted from extremely high energy waves, into the microwave region as the universe has expanded over time, stretching out the waves.
CMBR has a black body distribution with a peak of 2.7 kelvin
How is the relative abundance of hydrogen and helium evidence for the big bang?
During the big bang.
Hydrogen was converted into helium via nuclear fusion
The expansion of the universe caused it to cool to a point where outer space wasn’t hot enough to fuse elements
About 1/4 of all hydrogen produced was converted to Helium
The observed distribution of matter is 73& hydrogen and 25% helium which supports this claim.
What are Exoplanets
Planets that are not in our solar system
Why are exoplanets difficult to observe (3)
-Not direct light sources
-Light is obscured by the stars they orbit
-Too close to their star for a telescope of current technology to resolve them.
How do you detect an exoplanet via the Radial Velocity Method?
A Star and a planet will orbit their common centre of mass, this means the star will have tiny variations in its distance from earth. Shown by tiny red and blue shifts in its spectrum.
How do you detect and exoplanet via the Transit method
As a planet moves between the star it orbits and Earth, the stars apparent magnitude decreases slightly
We use this information to calculate the diameter of the planet
Very Low Chance of occurring
Use Hubbles Law to estimate the age of the Universe
Time = Distance/Velocity
Time = 1/ Hubbles constant
Turn Hubbles constant into ms-1 Mpc^-1
Multiply by 1 Mpc
1/S-1 = s
How are stellar absorption spectras produced?
When photons are absorbed by electrons within a star, so those particular wavelengths are not reflected back & not visible to sensors. This is shown by a black line
Only Certain photons of particular energies are absorbed by each element, this gives a fingerprint region that is unique for each element within the star that can be identified.
Draw the light curve for a planet orbiting in front of its star
