16 Cosmology Flashcards
What is Redshift?
Redshift is when objects moving away from us, are shifted towards the red end of the spectrum and the wavelengths of spectral lines become longer than the same corresponding wavelengths measured in a laboratory on Earth. It is an example of the Doppler Principle
What is the equation to calculate the change in wavelength?
λ - λ₀ . .v ------- = -- . .λ₀ . . .c λ = Observed wavelength λ₀ = True Wavelength v = Velocity c = Speed of light
Write out the Hubble’s Law.
v = H₀d H₀ = Hubble's Constant v = Velocity d = Distance
How can you determine the value of H₀?
Calculate the gradient of a v-d graph
What is the value of Hubble’s Constant (H₀)?
The accepted value is 68 km/s/Mpc
What is the Big Bang?
The Big Bang is a rapid expansion from an extremely high density to create the universe
What is the Steady State Model?
The Steady State Model suggests that the the Universe always has been expanding. The density of the Universe is constant over time with new matter being constantly created
What is a Cyclic Universe?
A Cyclic Universe suggests that there have been a series of Big Bang/ Big Crunch scenarios and will continue in the future
Which two theories state that overall density decreases with time?
Big Bang and Cyclic models
Which evidence supports the Big Bang model?
- Quasars
- Cosmic Microwave Background (CMB) Radiation
- Hubble Deep Field (HDF) image
How do Quasars support the Big Bang model?
Quasars are only found with high redshifts, which implies that they lie great distances from us and were created when the Universe was very young; the fact that quasars were more common in the early Universe compared with today which supports the nature of the Big Bang model
How do Cosmic Microwave Background (CMB) radiation support the Big Bang model?
Russian cosmologist George Gamow predicted if the early Universe was hot and dense, it would’ve cooled and expanded to a temperature just above absolute zero. In 1965, Robert Wilson accidentally discovered CMB radiation from all parts of the sky that corresponded to a temperature of 2.7 K
How does the Hubble Deep Field image support the Big Bang model?
These images were a series of long exposure images of empty space with a small field-of-view of 2.6 arcmins but the image revealed thousands of distant old galaxies, implying that the early Universe was very different from how it appears today
What are the three possible models for the expanding Universe?
- Decelerating Universe
- Coasting Universe
- Accelerating Universe
What does a decelerating Universe lead to?
A decelerating Universe leads to a collapse in a ‘Big Crunch’
What does a Coasting Universe lead to?
A Coasting Universe will continue to expand at a constant rate
If the expansion of the universe is Accelerating, what is fueling the expansion?
The expansion of the Universe is accelerating due to dark energy, a mysterious repulsive force, which increases the rate of expansion
How much of the Universe is believed to be made up of dark matter?
25%
Dark matter is used to explain what?
Gravitational Lensing
What is Gravitational Lensing?
Gravitational Lensing is the apparent bending of light from galaxies to form multiple images of the same galaxy
What is believed to be a form of black matter?
WIMPs (Weakly Interacting Massive Particles)
What is the relationship between velocity and distance?
Velocity and Distance are directly proportional to each other
How do you calculate recession velocity of a galaxy?
c(Δλ) -------- = v . .λ c = speed of light Δλ = Change in wavelength λ = Actual Wavelength v = Recession velocity
What is blueshift?
Blueshift is when light is shifted towards the shorter end of the spectrum, indicating that it is moving towards us
What is the Equant?
The Equant is a mathematical concept used to explain observed speed changes in planetary orbit in a geocentric system
What is an Epicycle?
The Epicycle is a geometric model that was used to explain the apparent change in speed and direction of the apparent motion of the planets. It was used in particular to explain retrograde motion
What is the most appropriate united for distances to galaxies?
Megaparsec
Why can the Hubble Constant given as an inverse of time?
The basic unit is the kilometre per second per megaparsec. The kilometre and megaparsec are both units of distance/length. These can effectively cancel to leave the unit as the ‘per second’
What is Hubble Time?
Hubble time is the time for which the Universe has been expanding
What are the approximate percentages of normal matter, dark matter and dark energy?
Normal matter - 5%
Dark Matter - 25%
Dark Energy - 70%
What is Hubble Time?
The age of the Universe - 14 billion years
What is Hubble length?
Hubble length is the length of the observable Universe
