Astrophysics

Question 1

Finding cosmic distance with parrallax

Answer 1

• applies to stars about 300 light years away (1 l.y = 9.5*10^15m)
• find angle between object and fixed point, then wait 6 months until the earth has reached the other end of its orbit and measure that angle again and find parallax angle
• closer = greater parallax
• 1 parsec = distance at which an object has a parallax angle of 1 arcsecond

Question 2

Radiation Flux

Answer 2

• Intensity = Radiation Flux(Wm^-2) = luminosity(w)/4pidistance^2

Question 3

Cepheid Variable stars

Answer 3

• luminosity of star varies with time, max luminosity is directly proportional to time period of luminosity variation
• By measuring the time period you can find max luminosity using T-L data, then use the radiation flux density to calculate distance from earth

Question 4

Standard Candle

Answer 4

• a distant object of known luminosity that we can find the distance of using radiation flux and use to compare distances

Question 5

Type 1a supernova

Answer 5

• a white dwarf star in a binary star system sucks matter off of its partner until it reaches a fixed threshold mass, at which point it explodes as a supernova. This threshold mass is always the same, and so they all have the same max luminosity
• can be used as standard candles

Question 6

Dark matter

Answer 6

• 24% of the universe is dark matter, which is what gives galaxies the mass they need to maintain structure as they don’t have enough hadronic matter
• Dark matter is only observable through it’s effect on other matter via gravity
• 71% is Dark energy, which causes acceleration of universes expansion

Question 7

Hertzsprung-Russell diagram

Answer 7

• measures luminosity against surface temperature, shows specific groups of stars in different stages of life
• luminosity is measured in multiples of the sun’s luminosity, surface temp goes from hot to cold along the x-axis

Question 8

Groups of stars

Answer 8

• main sequence = most stars spend most of their time here, larger stars spend less time here than smaller ones
• red giant = smaller stars cool and expand into this when they run out of hydrogen
• white dwarf = red giants cool to this when they run out of fuel
• supergiant = large stars expand into this when they run out of hydrogen, then explode in a supernova
• neutron stars/pulsars = the remnants of larger stars, spin very fast and emit radiation as a pulsar. The largest stars only leave a black hole

Question 9

Wien’s law

Answer 9

• Hot stars emit more blue light, cooler stars emit red light
• applies to black body radiators, like stars
• max wavelength emittedtemperature = 2.910^-3

Question 10

Stefan-Boltzmann

Answer 10

• Luminosity = 4piradius^25.6710^-8*temperature^4
• with measurement of radiation flux and max wavelength, and distance (from standard candle) we can find luminosity, temperature and radius in one go

Question 11

Black Bodies

Answer 11

• wiens law and stefan-boltzman law only apply to black bodies
• black bodies are perfect emitters and absorbers of em radiation, stars are close analogies
• at higher temperatures black bodies emit light with higher intensity, and the peak wavelength is shorter. Radiation curves are taller, thinner and the peak moves backwards with increasing temperatures