Section 4: Galaxies And Cosmology Flashcards
(25 cards)
Structure of our galaxy
Disc: diameter 30kpc; thickness 1.5kpc
Bulge surrounding nucleus - black hole
Halo: containing globular clusters
Appearance of Milky Way
Faint band of light with some darker patches
Globular cluster
Dense groups of relatively old stars
Determining rotation of galaxy
When an electron of a hydrogen atom reverses its spin it emits radiation wavelength 21 cm
This radiation can penetrate dust and earths atmosphere so this can be detected by radio telescopes
Doppler shift of received waves can be used to determine relative velocities of arms
Draw Hubble’s tuning fork diagram
See page 57
What type of galaxy is the Milky Way
Sb
What are the 4 types of active galactic nuclei
Radio galaxies
Seyfert galaxies
Quasars
Blazars
Radio galaxies
Elliptical
Intense source of radio waves
Emissions originate from pair of lobes on opposite sides of the galaxy
Seyfert galaxies
Spiral galaxies
Extremely compact but bright nuclei
Strong emissions of IR and X-Ray radiation
Quasars
Compact so look like stars
Emit huge quantities of energy in all regions of the spectrum from X-rays to radio
High red shift so v distant
Blazars
Appear starlike
Lie much closer than quasars
Can vary dramatically in optical brightness
Emit strongly from radio to gamma
What are AGNs powered by
Matter falling into a supermassive black hole that lies at the centre of the galaxy
Galaxies and type in local group
Andromeda (M31) - giant spiral
Large and small Magellanic Clouds - irregular
Triangulum (M33) - spiral
Pisces and Aquarius dwarf - dwarf
Cluster
Galaxies are found here
Have gravitational influence on each other
Often have giant elliptical galaxy in centre
Name 3 clusters
Virgo
Fornax
Coma
Superclusters
Collection of clusters grouped together by gravity
Doppler equation
See page 60
Hubble’s law
v = Hd
Velocity of recession = Hubble constant x distance (Mpc)
Value of Hubble constant
77 km/s/Mpc
Discovery of quasars
Investigation of radio source allowed astronomers to find a quasar and obtain its spectrum
Showed high red shift so far away
Age of universe
1 / H (km/Mpc cancel out)
13.8 billion years
Significance of CMB
If Big Bang theory correct bg temp of universe should have cooled to a few degrees above 0K -> corresponds to CMB radiation having temp of 2.7K
What did WMAP do
Study CMB in more detail to help cosmologists refine models of composition, evolution and age of universe
Provided data confirming existence of dark energy
Dark matter
Invisible to astronomers as it doesn’t emit or reflect radiation
Does have gravitational effects
