OP- D Astrophysics

Question 1

apparent brightness

Answer 1

amount of energy received per second per unit area by an observer (Wm-2)

Question 2

astronomical unit

Answer 2

the mean distance from the centre of the Earth to the centre of the Sun
(1.50 x 10^11)

Question 3

binary stars

Answer 3

two stars orbiting their common centre of mass

Question 4

three types of binary stars

Answer 4

• visual: can see two distinct stars
• eclipsing: periodic variation of brightness
• spectroscopic: change in wavelength of light receive from star (Doppler effect)

Question 5

cepheid variable

Answer 5

a star that undergoes a periodic expansion of its outer layers that gives a periodic variation in its luminosity

Question 6

Chandrasekhar limit

Answer 6

Maximum star remnant mass (1.4Ms) where electron degeneracy pressure prevent further gravitational collapse

Question 7

constellation

Answer 7

a group of star that appears to make a pattern in the sky but they may not necessarily be close to each other in space.

Question 8

cosmic microwave background (CMB) radiation

Answer 8

radiation emitted by the universe constituent with s temperature of 2.7K

Question 9

cosmic scale factor (R)

Answer 9

gives a measure of the expansion that has taken place in the universe

Question 10

dark energy

Answer 10

invisible energy source that my be accelerating the expansion of the universe

Question 11

electron degeneracy pressure

Answer 11

where electron repulsion prevents further gravitational collapse of a star

Question 12

galactic cluster

Answer 12

a group of galaxies bound together, orbiting around a common centre of gravity.

Question 13

galaxy

Answer 13

a large scale collection of stars, gas, and dust held together by gravity.

Question 14

globular stellar cluster

Answer 14

symmetrically arranged stellar cluster of 10^4 - 10^5 old stars

Question 15

Hertzsprung-Russell diagram

Answer 15

graph plotting luminosity of stars against their temperature

Question 16

Hubble’s Law

Answer 16

the speed at which galaxies are moving away from Earth (recession speed) is directly proportional to their distance from earth.

Question 17

L⊙ and M⊙

Answer 17

symbols for luminosity and mass of the Sun

Question 18

light year (ly)

Answer 18

the distance light travels in one year.

Question 19

luminosity (L)

Answer 19

total amount of energy emitted per second by a star (unit: W)

Question 20

main sequence star

Answer 20

a “normal” star that is fusing hydrogen into helium

Question 21

nebula

Answer 21

intergalactic cloud of dust and gas

Question 22

Newton’s model of the universe

Answer 22

the universe is infinite in space and time, uniform and static

Question 23

open stellar cluster

Answer 23

irregular shaped stellar cluster of several hundred young stars

Question 24

Oppenheimer-Volkoff limit

Answer 24

maximum star remnant mass (3M⊙) where neutron degeneracy pressure prevents further gravitational collapse.

Question 25

parsec

Answer 25

distance at which the angle subtended by the radius of the Earth’s orbit is one arc-second

Question 26

planetary nebula

Answer 26

the ejection of outer layers of a small star (< 4M⊙) once fusion has stopped

Question 27

planetary system

Answer 27

a group of planet orbiting a star

Question 28

pulsar

Answer 28

a rotating neutron star

Question 29

recession speed

Answer 29

the speed at which an object is moving away from an observer

Question 30

red giant (and supergiant)

Answer 30

• large (mass & surface area),
• relatively cool star,
• red in colour
• late stage in a star’s life cycle

Question 31

redshift

Answer 31

apparent increase in the wavelength of light from distant galaxies due to their motion away from us

Question 32

redshift ratio (z)

Answer 32

ratio of change in wavelength due to the Doppler effect to original wavelength emitted by a galaxy moving relative to Earth.

Question 33

singularity

Answer 33

point containing the entire universe at the start of the Big Bang.

Question 34

stellar cluster

Answer 34

a close group of gravitationally bound stars, gas and dust (within a galaxy)

Question 35

stellar parallax

Answer 35

method used to measure distances to stars based on their apparent movement in position relative to distant background stars over a 6 month period.

Question 36

supercluster

Answer 36

a large grouping of galactic clusters

Question 37

supernova

Answer 37

the ejection of the outer layers of a large star (> 8M⊙) once fusion has stopped.

Question 38

type Ia supernova

Answer 38

type of supernova with a known luminosity that occurs in binary star systems where one of the stars is a white dwarf.

Question 39

white dwarf

Answer 39

• small (mass & surface area)
• relatively hot star
• white in colour
• final stage for a small star
• no longer fusion, cooling down