Astrophysics EP Flashcards
Explain the problem of using the transit method to detect a small planet
(k) transit measures how much light is blocked by a planet
The planet is small so little light is blocked
What is meant by Rayleigh criterion
The minimum subtended angle between two objects who image can be resolved
the central maximum of one object coincides the first minimumof the other
What is meant by standard candles
Objects whose absolute magnitude is known
What formula do you use to find temperature using a graph of wavelength
Wiens
What is the absolute magnitude of type 1a supernova
-19.3
How do you draw a type 1a supernova graph
Absolute magnitude -20 to -12
X axis from 0 to 400 days in 100 days interval, peak at 0
How does the measure of supernovae type 1a lead to a controversy concerning the behaviour of the universe
Measurements of the supernova does no agree with Hubble’s law
So the universe must be expanding at an increasing rate
Must be due to dark energy
Why does B class stars have prominent Hydrogen Balmer absorption lines?
B class stars are hot enough to have hydrogen in n=2 state
Describe the main features of the radial velocity method in detection of planets
There is a periodic doppler shift in light from the stars
Due to the star and planet orbiting a common centre of mass
Why is a nearby red giant dangerous for life on earth
As the star may collapse and become a supernova, which produces gamma ray burst
The gamma would kill our cells
Why would supernovas not be in HR diagram
Absolute magnitude is around 20
temperature would be too high
Why would black holes not be in the HR diagram
Black holes escape velocity is greater than speed of light so no light is emitted
black holes are too cold to be put in the scale
What is meant by cosmological microwave background radiation?
Radiation from all over the universe
When the universe has cooled sufficiently to decouple matter and radiation
Radiation has been red shifted to microwaves as the universe expands
Explain how the abundance of hydrogen supports the big bang theory?
Suggests fusion occurred between hydrogen to form helium during the big bang
However as the universe began to cool down and expand, fusion stopped
as a result there is a relative abundance of hydrogen and helium
What causes a variation in wavelength
The doppler effect
What star is small but hot
White Dwarf star
What star is big but cool
red giants
Why do we use hydrogen balmer for the analysis of wavelengths on class A stars
As Hydrogen balmer lines are strongest for class A stars meaning they’re more easily measured.
Explain how an orbiting planet causes a doppler shift in the spectrum of a star
Planets and stars orbit around a common centre of mass that means it moves away from earth as it orbits
As a result wavelengths of light received from stars shift.
define absolute magntude
It is the apparent magnitude from 10pc away
same spectral class indicates what two things in common?
temperature
colour (spectral lines)
define a black hole
When escape velocity is higher than speed of light
how to work out the age of the universe
1/H * MPC / 10^3 = time
What is red shift
The increase in wavelength due to recessional velocity between the source and observer
Explain why type 1a supernovae can be used as standard candles to determine distances
As apparent magnitude can be measure
The peak absolute magnitude is the same
Why is it important for astronomers to have several independent methods of determining the distance to galaxies
To make accepted value for distances for reliable
3 marks, how existence of cosmological microwaves explain prove the big bang
Radiation like gamma rays come from all around the universe
as the universe cooled and expanded, matter and radiation decoupled
due to red shift, as the universe was expanded the cosmological gamma rays expanded to microwaves
3 marks, explain for the existence of abundance of hydrogen and helium explain occurrence of the big bang
Brief period of fusion of created the abundance of hydrogen and helium
as the universe expanded and cooled the fusion stopped
3:1 ratio of hydrogen and helium in the universe
What to look at when confirming if a pair of stars are in a binary system or not
- compare the colour via the spectral class due to temperature
- Ratio of brightness, how many times brighter
- comparing power output
pc = o a T^4
same distance meaning binary system
What to compare between reflecting telescope and radio telescope
- resolving power (minimum angular resolution)
- collecting power
- position
- structure
Compare the position and structure of reflecting telescope and radio telescope (similarities and differences)
Positioning
Both can be ground based
- reflecting needs to be at higher altitudes due to absorption of atmosphere, water vapour, ozone layer and pollution
- radio telescope needs to be in quiet places but can be on the ground
Structure; both use parabolic mirror or dish
- reflecting has secondary mirror
- radio can be made out of wired mesh
describe main features of radial velocity method of detecting exoplanets
Measure periodic doppler shifts in light received from the star
Star and planet orbiting a common centre of mass
Measuring of distant quasars, what is one problem
Due to dark energy, universe is constantly accelerating when expanding
Uses hubbles law or inverse square law is unreliable over large distances
describe radial velocity/doppler effect
- both orbit a common centre of mass
- exoplanet orbits a star, only a star emits light
- star wobbles causing a variation in red shift
describe transit method
exoplanet that does not emit light periodically cover the star
- size of dip in light shows size of star
- time period show orbiting period
why may a quasar no longer emit radiation
quasars are formed around black holes
black holes no longer have radiation falling into them
Why
