Cosmology

Question 1

What do the components of the Doppler effect equation mean?

Answer 1

Question 2

What is the fractional change in wavelength also known as

Answer 2

the redshift

Question 3

What does the redshift equation say about wavelength and frequency

Answer 3

if the source moves away from the observer then:
The wavelength increases
The frequency decreases

Question 4

Draw a diagram showing the doppler shift of light

Answer 4

Question 5

Describe what is observed (in terms of relative velocity and wavelength change) when a star approaches/ recedes from the earth

Answer 5

• If the star is approaching the Earth, blueshift is observed (negative z):
  The relative velocity v is positive
  The change in wavelength increment lambda is negative
• If the star is receding from the Earth, redshift is observed (positive z):
  The relative velocity v is negative
  The change in wavelength increment lambda is positive

Question 6

Which type of light (red or blue) has a longer/shorter wavelength and frequency

Answer 6

red light - has a longer wavelength and a lower frequency
blue light - has a shorter wavelength and a higher frequency

Question 7

eclipsing binary star system def

Answer 7

Where two stars orbit around a common centre of mass with their orbital plane in the Earth’s line of sight

They are always pi out of phase

Question 8

By what can the stars in an eclipsing binary star system be identified by

Answer 8

from their characteristic light curves

Question 9

Draw the light intensity curve of an eclipsing binary

Answer 9

Question 10

Describe the primary and secondary minima on a light intensity curve of an eclipsing binary AND what they are caused by

Answer 10

• The primary minima (the larger dip) are caused by the larger star passing in front of the smaller star
• The secondary minima (the smaller dip) are caused by the smaller star passing in front of the large star

Question 11

What does it mean when spectral lines from a distant galaxy are redshifted

Answer 11

The lines have shifted towards a longer wavelength, or towards the red end of the spectrum

Question 12

Describe and draw a diagram for how we can observe the redshift of distant galaxies

Answer 12

Question 13

Describe the expansion of the universe

Answer 13

Question 14

What is the equation linking velocity, time period and radius of a binary star system

Answer 14

Question 15

What is an eclipsing binary

Answer 15

• binary star systems that orbit in the same plane as the line of sight

Question 16

Quasars/ quasi-stellar object def

Answer 16

Extremely luminous star-like sources of radiation with very high redshifts

Question 17

What are quasars notable for

Answer 17

• strong radio emissions
• High luminosities
• Extremely large redshifts
• Small size

Question 18

Describe the formation of quasars

Answer 18

• quasars are a type of active galactic nucleus, meaning they are supermassive black holes, surrounded by an accretion disc of matter
• They are found at the centre of extremely distant galaxies
• When they become active, i.e. when matter falls into it, they become quasars
• As matter falls into the black hole, jets of radiation are emitted from the poles
• The gravitational potential energy of infalling matter is transferred to electromagnetic radiation
• Now it is known that quasars are strong emitters of all wavelengths, not just radio waves
• Quasars are formed around black holes
• When the black hole no longer has matter falling into it, the quasar will stop emitting radiation

Question 19

What does the high redshift of quasars explain about quasars and the universe

Answer 19

• Quasars are thought to be some of the most distant measurable objects in the known universe
• This allows astronomers to see very far back to an early Universe as it was not long after the Big Bang

Question 20

what is the absolute magnitude of the sun

Answer 20

5

Question 21

surface temperature of the sun

Answer 21

6000k

Question 22

star classification of the sun

Answer 22

class g

Question 23

What does Hubble’s law state

Answer 23

The recessional velocity of a galaxy is proportional to its distance from Earth

Question 24

Hubble’s law equation

Answer 24

Question 25

What does Hubble’s law show

Answer 25

- The further away a star is from the Earth, the faster it is moving away from us - The closer a star is to the Earth, the slower it is moving away from us

Question 26

Describe Hubble’s law in relation to estimating the age of the universe

Answer 26

Question 27

What are the key 3 pieces of evidence for the Big Bang theory

Answer 27

Question 28

Describe what dark energy is and its controversy

Answer 28

Question 29

Describe the controversy concerning the behaviour of the universe

Answer 29

- Measurements of supernovae do not agree with predictions from Hubble’s law - So the universe must be expanding at an increasing rate (it is accelerating) - This is controversial as there is no known energy source for expansion, or reference to dark energy