Cosmology COPY Flashcards
What is the doppler effect?
Effects the electromagnetic waves from stars and glalaxies. For a source moving away from the observer there is an apparent increase in the wavelength
What is the doppler effect equation?
∆wavelength / wavelength if source was still = v/c
v = velocity of star
c = speed of light
When does the doppler effect equation work
As long as the velocity of the source is a lot less than the velocity of the wave
What is the doppler effect equation corrisponding to frequency?
∆f / f = v / c
What does the doppler effect say for waves moving towards the observer?
The wavelength would appear to decrease and the frequency to increads
What happens to the change in frequency, as effected by the doppler effect, if the observer sends waves put which then bounce off the moving object
The change in the frequency, ∆f, is doubled do:
∆f / f = 2v/c
What is red shift? Blue shift?
For a source moving away from the observer the wavelength increases moving the lines towards the red of the spectrum
For a source moving towards the observer there would be a blue shift
What is the red shift equal to?
The ratio of ∆wavelength / wavelength
v/c
What does ‘at a redshift of …’ mean?
The ratio of ∆wavelength / wavelength is …
What are binary stars?
Two stars which circulate around each other so=round each other about a common axis
What is the time periof of the motion of two binary stars?
1 on frount, the 2 then 2 again
Why do the dips in luminosity for binary stars vary?
The big dip is when the dimmer star blocks light from the brighter star and vise versa
When is the maximum intensity seen for a binary star system?
When both starts can be seen
How can the mass of a binary star using the Doppler Shift
Define exoplanets
Planets that are not in our solar system
Why are exoplanets difficult to resolve?
- They don’t give out much light and so the light from the star which they are orbiting drowns out this reflected light
- They are so small that most telescopes do not have a good enough resolving power to distinguish them from the star they are orbiting
Explain the ‘wobble’ from a star
- When an exoplanet orbits a star, the exoplanet and the star orbit about their centre of mass
- As the star is more massive than the planet, the centre of the mass will be mich closer to the star
- The star will ‘wobble’ about this centre of mass
- When the star wobbles towards towards an observer, the light will be slightly blue shifted. It will be red shifted when the star moves away.
- If doppler shifts are detected then it suggests the prescence of an exoplanetand the minimum mass can be detected