5.5 - Astrophysics and Cosmology

Question 1

What is Nuclear Fusion?

Answer 1

The process of two nuclei joining together and releasing energy from a change in binding energy

Question 2

What is Gravitational Collapse?

Answer 2

The inward movement of material in a star due to the gravitational force caused by its own mass. Star formation is due to the gravitational collapse of a cloud of gas and dust. Gravitational collapse occurs in a mature star when the internal gas and radiation pressure can no longer support the stars own mass

Question 3

What is Radiation Pressure?

Answer 3

It is due to the momentum of petitions released in fusion reactions, and acts outwards (in the direction of the energy flow)

Question 4

What is Gas Pressure?

Answer 4

It is related to the temperature and volume of a gas using pV=nRT, and also to the mean square speed of the gas atoms using pV=1/3Nmc^2. Gas pressure acts in all directions at a point inside a gas, such as inside a star

Question 5

What is a Main Sequence star?

Answer 5

A star in the main part of its life cycle, where it is fusing hydrogen to form helium in its core. The main sequence stars are shown as a curved band on a plot of a star’s luminosity against temperature.

Question 6

What is a Red Giant?

Answer 6

A star in the later stances of its life that has nearly exhausted the hydrogen in its core and is now fusing helium nuclei. It is bigger than a normal star because it’s surface layers have cooled and expanded

Question 7

What is a White Dwarf?

Answer 7

The end product of a low-mass star, when the outer layers have dispersed into space. A white dwarf is very dense, with a high surface temperature and low luminosity.

Question 8

What is a Planetary Nebula?

Answer 8

An expanding, glowing shell of ionised hydrogen and helium ejected from a red giant star at the end of its life

Question 9

What is Electron Degeneracy Pressure?

Answer 9

The pressure that stops the gravitational collapse of a low-mass star. This is the pressure that prevents a white dwarf star from collapsing

Question 10

What is the Chandrasekhar Limit?

Answer 10

The maximum possible mass for a stable white dwarf star and it equal to 1.4 times the mass of our Sun. White dwarfs with masses above this will collapse further to become neutron stars or black holes

Question 11

What is a Red Super Giant?

Answer 11

A star that has exhausted all the hydrogen in its core and has a mass much higher than the Sun

Question 12

What is a Supernova!

Answer 12

A huge explosion produced when the core of a red super giant collapses

Question 13

What is a Neutron Star?

Answer 13

The remains of the core of a red super giant after it has undergone a supernova explosion. It is incredibly dense and composed mainly of neutrons

Question 14

What is a Black Hole?

Answer 14

The core of a massive star that has collapsed almost to a point. Black holes are very dense and very small, with a gravitational field so strong that light cannot escape

Question 15

What is the Hertzsprung-Russel Diagram?

Answer 15

A luminosity temperature graph

Question 16

What is the Luminosity of a star?

Answer 16

The total energy that the star emits per second

Question 17

What is a Continuous Spectrum?

Answer 17

A spectrum that appears to contain all wavelengths over a comparatively wide range

Question 18

What are Energy Levels?

Answer 18

The specific energies that electrons can have when occupying specific orbits. Electrons can only occupy these discrete energy levels and cannot exist at other energy values between them

Question 19

What is the Emission Line Spectrum?

Answer 19

The spectrum of frequencies of electromagnetic radiation emitted due to electron transitions from a higher energy level to a lower one within an atom of that element. Since there are many possible electron transitions for each atoms, there are many different radiated wavelengths. A line spectrum consists of a series of bright lines against a dark background

Question 20

What is an Absorption Spectrum?

Answer 20

The pattern of dark lines in a continuous spectrum from a light source and is cause by light passing through an absorbing medium such as a gas. The dark lines represent the wavelengths that are absorbed

Question 21

What is a Transmission Diffraction Grating?

Answer 21

A glass surface having a large number of very fine parallel grooves or slits, and used to produce optical spectra by diffraction of transmitted light

Question 22

What are Maxima?

Answer 22

Regions of brightness which will be seen when the path difference between overlapping waves is equal to a whole number of wavelengths

Question 23

What is Wein’s Displacement Law?

Answer 23

Is states that the wavelength of maximum luminosity is proportional to 1/Temperature. It is used to estimate the peak surface temperature of a star from the wavelength at which the stars brightness is maximum

Question 24

What is Stefan’s Law?

Answer 24

It relates the luminosity, L, of a star with its absolute temperature, T. L=4(pi)r^2AT^4 where A is known as Stefan’s Constant and has a value of 5.67x10^-8

Question 25

What is Luminosity?

Answer 25

The total energy that a star emits per second

Question 26

What is the Astronomical Unit (AU)? And what is it’s value?

Answer 26

The mean distance from the centre of the Earth to the centre of the Sun. It is equal to 1.496x10^11

Question 27

What is a Parsec?

Answer 27

A unit of distance that gives a parallax angle of 1 second of arc (1/3600 of a degree), using the radius the the Earth’s orbit (1AU) as the baseline of a right-angled triangle. One parsec is approximately equal to 3.1x10^16m

Question 28

What is Stellar Parallax?

Answer 28

The apparent shifting in position of a star viewed against a background of distant stars when viewed from different positions of the Earth, such as at different positions of the Earth’s orbit around the Sun

Question 29

What is a Light-Year?

Answer 29

The distance travelled by light in one year. One light-year is approximately equal to 9.5x10^15m

Question 30

What is the Doppler Effect?

Answer 30

The change in wavelength caused by the relative motion between the wave source and an observer. For electromagnetic radiation of frequency f and wavelength L, the Doppler equation is (change in f)/f = (change in L)/L

Question 31

What is Red Shift?

Answer 31

The apparent increase in wavelength of electron magnetic radiation caused when the source is moving away, relative to the observer

Question 32

What is Hubble’s Law?

Answer 32

It states that the recessional velocity of a galaxy is directly proportional to its distance from the Earth

Question 33

What is the Hubble Constant?

Answer 33

The constant proportionality in the equation v=Hd where h is Hubble’s Constant

Question 34

What is Cosmic Microwave Background Radiation?

Answer 34

Microwave radiation received from all over the sky originating from after the Big Bang, when the universe cooled to a temperature near 3000k. As the universe has expanded this radiation is now just a faint microwave glow with a peak wavelength corresponding to a temperature of 2.7K

Question 35

What is the Big Bang Theory?

Answer 35

It states that the universe was created from a single point where all of the universe’s current mass was situated. At the time of its creation, the universe was much smaller, hotter and denser than it is now. Time and space were both created at the instant of the Big Bang

Question 36

What is the Cosmological Principle?

Answer 36

It states that on a large scaled the universe is isotropic (the same in all directions) and homogeneous (of uniform density as long as a large enough volume is considered)

Question 37

What is Dark Matter?

Answer 37

Matter which cannot be seen and that does not emit or absorb electromagnetic radiation. It is not detected directly, but is detected indirectly based on its gravitational effects relating to either the rotation of galaxies or by gravitational lending of starlight

Question 38

What is Dark Energy?

Answer 38

A type of energy that permeates the whole universe and opposes the attractive force of gravitation between galaxies via the exertion of a negative pressure. It is not detected directly, but we know it exists because we now know the universe is accelerating as it expands