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PHYS 183 Lecture Notes - Cygnus X-1, Stellar Evolution, Irregular Galaxy

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PHYS 183
Tracy Webb

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PHYS 183 The Milky Way Inside and Out Tracy Webb Winter 2013
Lecture 28: March 22nd, 2013
recall: blackholes are supernovas that continue to collapse
recall: mass tells space how to curve and space tells matter how to move this is space-time
gravitational redshift
o redshift is the stretching of light to longer wavelengths
o each wavelength has a different energy associated
o if a light is stretched to redshift it also has less energy
o to get out of a blackhole you need enough energy photon needs the same thing
o light loses energy as it climbs out of a blackhole infinite redshift
o the light will be redshifted just from climbing out of the blackhole
o this is something we can actually measure
time dilation
o time is relative you experience time at a different rate at different velocities
o we can measure this with atomic clocks but not human beings
o time slows down near a blackhole
o slows to infinity at the event horizon
o if you watched your friend fall into a blackhole time would slow down as they got closer to
it and so you would never actually see them enter the blackhole
detecting blackholes in binaries can see the matter spiralling in
o can determine mass of accreting object & show it is >3 solar masses
o in such a small area there is nothing else it could be
Cygnus X-1 is a blackhole we can see from Earth (not with your eyes) x stands for x-ray force
Chapter 20: Galaxies and Modern Cosmology
the Milky Way is the most famous galaxy in the universe
o it is a spiral galaxy looks like a pinwheel
o different colours due to different ages of stars in different stages of stellar evolution
o if you turn it on it’s side you will see a large bulge in the middle of the disk
o the whole thing rotates we are orbiting around the centre of the galaxy
o the centre of the galaxy is a blackhole
o there is a dark matter halo around the centre
o length of galaxy is 100 000 light years
the Hubble Deep Field shows that the universe is full of galaxies
there are 3 major types of galaxies
o spiral galaxy
where we live
disk component: stars of all ages, dust & gas clouds
bulge & halo components: old stars, not much gas or dust
o elliptical galaxy
much redder
looks like big star
it is the light of billions stars together
shaped like footballs
biggest galaxies in the universe
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