9.3 Cosmology Flashcards
What is the Doppler effect?
The apparent change in wavelength and frequency of a wave, when the source moves relative to the observer.
How does the wavelength change if the source moves towards the observer?
The wavelength decreases.
(Frequency increases)
This is blueshift
How does the wavelength change if the source moves away from the observer?
The wavelength increases.
(Frequency decreases)
This is redshift
What is the Doppler equation in terms of wavelength?
(Also the equation for redshift)
What do the letters represent in this equation?
What is the Doppler equation in terms of frequency?
What do the letters represent in this equation?
What is a binary star system?
A system consisting of two stars rotating about the same centre of mass.
Describe what is happening with the two stars.
- No eclipse, maximum brightness.
- Larger star infront of smaller star, primary minimum
- No eclipse, maximum brightness.
- Smaller star infront of larger star, secondary minimum
State Hubble’s law.
Recession velocity is proportional to distance from Earth.
What do the letters represent in this equation?
How can Hubble’s law be used to estimate the age of the Universe?
And converting from km s-1 Mpc-1 to years
What do the letters represent in this equation?
What is the Big Bang?
13.8 billion years ago, the Universe expanded from an extremely hot and dense point, and is still expanding today.
What is the Cosmic Microwave Background and why is it evidence for the Big Bang?
is radiation that can be observed throughout the universe - the Big Bang can explain its existence as being the result of high energy radiation produced in the big bang that has been stretched as the universe has expanded.
How is relative abundence of Hydrogen and Helium used as evidence for the Big Bang?
The Big Bang theory predicts that early fusion reactions produced helium by fusing hydrogen, before the universe cooled and expanded to leave a relative abundance of those two elements.
What is a quasar?
An Active Galactic Nucleus; a supermassive black hole surrounded by an infalling disc of matter. As the matter falls in, jets of radiation are emitted from the poles.
What were quasars first thought to be?
Star like strong radio sources.
Quasi-stellar radio source
What suggests that quasars are extremely distant objects?
Large optical redshift.
What is an exoplant?
A planet not in our solar system.
What makes observing exoplanets difficult?
- Their light is obscured by their parent stars
- They tend to be too close to their parent stars for a telescope to resolve them
What are two methods for detecting exoplanets?
- Radial velocity method
- Transit method
Describe the radial velocity method.
A star and planet orbit their common centre of mass, causing the star’s distance from Earth to vary slightly, these variations are shown by red and blue shifts in its spectrum.
Describe the transit method.
As a planet passes between the star and Earth, the star’s brightness appears to decrease. This can be used to calculate the diameter of the planet.
What is are difficulties with the transit method?
- Exoplanet orbit needs to be edge on to Earth
- Exoplanet needs to have a small orbit
Draw a typical light curve for the transit method.
