Cosmology Flashcards
What is redshift?
Absorption lines of galaxy moving away are shifted to the left (red end)
Bigger velocity → Bigger redshift
What is blueshift?
Absorption lines of galaxy moving towards are shifted to the right (blue end)
Bigger velocity → Bigger blueshift
How can we potentially tell if a galaxy is rotating?
One side is redshifted
Other side is blueshifted
If a galaxy does not have one side redshifted and one side blueshifted
could it still be rotating?
Yes, if the rotation isn’t along the line between the galaxy and Earth
How do you calculate the velocity of a galaxy given its redshift?
v = zc
Is a redshift velocity the true velocity of a star?
No, the star could have a v|
For this binary star system
- When is redshift of star A maximum?
- When is redshift = 0?
- When is blueshift maximum?
What is Hubble’s law?
A galaxy’s recessional velocity is proportional to its distance from Earth
v ∝ d
How can you use this graph to calculate the age of the Universe?
(Reciprocal of the gradient)
Why does this graph not mean Earth is at the centre of the Universe?
This graph would be produced if you took measurements from any galaxy
All galaxies are moving away from every other galaxy
What is the radial velocity method?
Small redshift of star caused by exoplanet
Used to identify exoplanets
What is the transit method?
Regular dip in brightness of star due to exoplanet passing in front
What is an exoplanet?
A planet in another solar system
Why are exoplanets so difficult to detect?
Exoplanets don’t emit light, they only reflect
And it is a tiny amount compared to the star
What are the key stages of the Big Bang Theory?
1 Photons produce particles of matter & antimatter from a vacuum
2 An excess of matter over antimatter occurs
3 Nuclear fusion occurs
4 Nuclear fusion stops
5 Atoms form
6 Stars & galaxies form
7 Nuclear Fusion occurs in stars
8 Life starts
What is the main evidence in support of the big bang?
Explain what it is
Cosmic Microwave Background
Radiation leftover from when the Universe formed neutral atoms
(redshifted to microwaves as Universe has expanded)
What is a Quasar?
Very luminous galaxy nucleus where mass is spiraling into the supermassive blackhole at the center
What is required for a quasar to form?
An accretion disk (gas, dust and matter) close to the supermassive black hole at the center
Why can’t most quasars be detected?
Only detected if Earth is in line with radiation jets
Why are radiowaves detected from a Quasar?
Emitted radiation is massively redshifted to radiowaves
What does the large redshift of Quasars tell us about Quasars?
They are some of the most distant objects in the Universe
What is the Schwarzschild Radius for an object?
What it’s radius would have to be shrunk to for it to become a black hole
(where escape velocity > speed of light)
How do Type 1A Supernovae Form?
- In a binary star System
- One star has become a White Dwarf
- But has absorbed enough mass from other so M > 1.4xMSun
What are Type 1A Supernovae useful for?
One of the brightest ‘Standard Candles’ (known Absolute Magnitude)
Used to measure distances to furthest galaxies
What is the Absolute Magnitude curve for a Type 1A Supernovae?
What do the redshifts of the most distant Type 1A Supernovae tell us?
The redshifts are greater than expected
So Universe’s expansion is accelerating
Dark energy causes this acceleration
In the equation for doppler shift what do the different λ represent?
λ0 → Wavelength if observer was stationary
∆λ → observed λ - λ0
