Section 4: Galaxies And Cosmology

Question 0

Structure of our galaxy

Answer 0

Disc: diameter 30kpc; thickness 1.5kpc
Bulge surrounding nucleus - black hole
Halo: containing globular clusters

Question 1

Appearance of Milky Way

Answer 1

Faint band of light with some darker patches

Question 2

Globular cluster

Answer 2

Dense groups of relatively old stars

Question 3

Determining rotation of galaxy

Answer 3

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

Question 4

Draw Hubble’s tuning fork diagram

Answer 4

See page 57

Question 5

What type of galaxy is the Milky Way

Answer 5

Sb

Question 6

What are the 4 types of active galactic nuclei

Answer 6

Radio galaxies
Seyfert galaxies
Quasars
Blazars

Question 7

Radio galaxies

Answer 7

Elliptical
Intense source of radio waves
Emissions originate from pair of lobes on opposite sides of the galaxy

Question 8

Seyfert galaxies

Answer 8

Spiral galaxies
Extremely compact but bright nuclei
Strong emissions of IR and X-Ray radiation

Question 9

Quasars

Answer 9

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

Question 10

Blazars

Answer 10

Appear starlike
Lie much closer than quasars
Can vary dramatically in optical brightness
Emit strongly from radio to gamma

Question 11

What are AGNs powered by

Answer 11

Matter falling into a supermassive black hole that lies at the centre of the galaxy

Question 12

Galaxies and type in local group

Answer 12

Andromeda (M31) - giant spiral
Large and small Magellanic Clouds - irregular
Triangulum (M33) - spiral
Pisces and Aquarius dwarf - dwarf

Question 13

Cluster

Answer 13

Galaxies are found here
Have gravitational influence on each other
Often have giant elliptical galaxy in centre

Question 14

Name 3 clusters

Answer 14

Virgo
Fornax
Coma

Question 15

Superclusters

Answer 15

Collection of clusters grouped together by gravity

Question 16

Doppler equation

Answer 16

See page 60

Question 17

Hubble’s law

Answer 17

v = Hd

Velocity of recession = Hubble constant x distance (Mpc)

Question 18

Value of Hubble constant

Answer 18

77 km/s/Mpc

Question 19

Discovery of quasars

Answer 19

Investigation of radio source allowed astronomers to find a quasar and obtain its spectrum
Showed high red shift so far away

Question 20

Age of universe

Answer 20

1 / H (km/Mpc cancel out)

13.8 billion years

Question 21

Significance of CMB

Answer 21

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

Question 22

What did WMAP do

Answer 22

Study CMB in more detail to help cosmologists refine models of composition, evolution and age of universe
Provided data confirming existence of dark energy

Question 23

Dark matter

Answer 23

Invisible to astronomers as it doesn’t emit or reflect radiation
Does have gravitational effects

Question 24

Dark energy

Answer 24

Source of force accelerating expansion of universe