3.9.3 Cosmology Flashcards
What is meant by the Doppler effect?
The compression or spreading out of waves that are emitted or reflected by a moving source.
What is the formula for red shift?
z = v/c = ∆f/f = -∆λ/λ
How can the Doppler effect be used to identify binary star systems?
The star is travelling towards the observer, its wavelength is blueshifted, when its travelling away, its wavelength is redshifted.
What is the light curve of eclipsing binaries?
wave…thing
1. no eclipse at maximum brightness
2. larger star in front of smaller star, big dip
3. no eclipse, maximum brightness again
4. smaller star in front of larger star, partially blocking its light, secondary minimum occurs
What is Hubble’s law?
A galaxy’s recessional velocity is directly proportional to its distance from the Earth. (the universe is expanding from a common point)
What is the formula for Hubble’s law?
v = Hd
v = recessional velocity
H = Hubble constant (65 kms^-1Mpc^-1)
d = distance from the Earth
How can the age of the universe be calculated?
Rearrange Hubble’s formula to
H = v/d ,
hence 1/H = d/v = t
convert units to seconds
What evidence is there for the Big Bang?
CMBR - the universe is assumed to have began at one point which was infinitely hot and small. There was a huge explosion from this point. When the Big Bang happened, there was thought to be high energy radiation everywhere, as the universe expanded and cooled, the radiation would have lost energy and red shifted (the remains are CMBR).
H to He ratio - during the early stages, nuclear fusion converted hydrogen nuclei to helium nuclei, this lasted a short period of time before the universe cooled and fusion stopped. Relative abundance ratio of H to He is 3:1.
What is a quasar?
An active galactic nucleus - a supermassive black hole surrounded by a disc of matter, which causes jets of radiation to be emitted from the poles as it falls in.
What are the features of quasars?
Extremely large optical red shifts
Very powerful light output
Size is not much bigger than a star
(most distant measurable objects in the universe)
What are exoplanets?
Planets not within our solar system
What are the 2 methods of detecting exoplanets?
Radial velocity method
Transit method
Describe the radial velocity method
The star and planet orbit a common mass, causing the star to ‘wobble’ slightly. This causes a Doppler shift in the light received from the star. It is more noticeable on high mass planets since they have greater gravitational pull on the star. The time period of the planet’s orbit is equal to the time period of the Doppler shift
Describe the transit method
Involves observing the intensity of light output of a star. If a planet passes in front of a star, the intensity dips.
The size and orbital period of the planet can be determined from the amount that intensity falls by and the duration of the dip respectively.
What is a limitation of the transit method?
Only works if the line of sight to the star is in the plane of the planet’s orbit - more likely for planets with small orbits (because most orbits are inclined, so the smaller the orbit the more likely the planet is to pass in front of the star)
