The Milky Way and Other Galaxies Flashcards
What are the main properties of the milky way?
Mainly a disc with spiral arms. Also with a bulge and halo.
About how many stars are in the milky way?
~3*10^11 stars
Name some properties of the milky way.
- Perseus arm at far left
- Orion arm at top
- Sun near orion arm
- ~8500pc across
- ~500pc deep
What is the distribution of globular clusters like in the milky way?
Roughly spherical. Not centred at Sun though.
What radius does the sun orbit the centre of the galaxy? What velocity?
R0 = 8.5kpc v0 = 220 km s^-1
How do you work out an equation for the mass of a star?
Set gravitational force equal to centripetal acceleration and rearrange for mass.
What does a galaxy rotation curve show us?
That stellar count rapidly drops as a function of distance to the centre.
What is the Milky way rotation curve like and what does this suggest?
Is flat - suggests there is something else other than stars mass, otherwise it would decrease with radius.
What is dark matter?
Unknown mass surrounding galaxies which is seen through gravity but does not appear to emit light.
How do we know there are black holes at the centre of galaxies?
Because from the equation for mass, we can see that the central mass is way to large to be a cluster of stars.
How can we estimate how far other galaxies are?
Need something bright which we can estimate the absolute magnitude of and then use the magnitude equation to find out distance.
What are Cepheid variables?
- Cepheids undergo oscillations in their envelopes - they are in the giant star phase
- Their oscillations are visible as changes of brightness with periods of ~10 days
- Was discovered that the pulsation period is related to the luminosity of the star
What is the equation relating luminosity and period?
Mv = -2.81*log P(d) - 1.43
What are the requirements for standard candles?
- Bright
- Recognisable
- Can be calibrated (need a luminosity)
What absolute magnitude do we find for Cepheids of approximate periods of 10-100days?
Mv ~ -2 to -7 or L = 500-50000 L(sun)
What is the distance to the Andromeda galaxy?
770 pc
What is the net velocity of the Milky way and where is it heading?
110 km s^-1 and is heading for the Andromeda galaxy
How long will it take for the milky way to reach andromeda?
4 billion years
What is the equation for fractional redshift?
z = (λ’-λ0)/λ0 = v/c
What did Vesto Slipher find about near/far galaxies?
The near galaxies are getting close but the far galaxies are moving away from us and eachother
What is Hubble’s law of universal expansion?
Galaxies recede from us with a velocity v that is proportional to the distance d: v = H0d, where H0 is the Hubble constant
What is the modern value of the Hubble constant?
68-72 km s^-1 Mpc^-1
What are the two main types of supernovae?
Type 2 - core collapse
Type 1a - white dwarfs pushed over the Chandrasekhar limit
What does the light curve for a type 1a supernova look like?
Increases and then peaks and then decreases, levelling out at the end
How can we use type 1a supernova?
Can use them to find distance as they are very bright and can be calibrated to give luminosity (Mv ~ -19)
