5.5 - Astrophysics and Cosmology Flashcards Preview

OCR Physics A Level > 5.5 - Astrophysics and Cosmology > Flashcards

Flashcards in 5.5 - Astrophysics and Cosmology Deck (38):

What is Nuclear Fusion?

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


What is Gravitational Collapse?

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


What is Radiation Pressure?

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


What is Gas Pressure?

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


What is a Main Sequence star?

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.


What is a Red Giant?

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


What is a White Dwarf?

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.


What is a Planetary Nebula?

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


What is Electron Degeneracy Pressure?

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


What is the Chandrasekhar Limit?

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


What is a Red Super Giant?

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


What is a Supernova!

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


What is a Neutron Star?

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


What is a Black Hole?

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


What is the Hertzsprung-Russel Diagram?

A luminosity temperature graph


What is the Luminosity of a star?

The total energy that the star emits per second


What is a Continuous Spectrum?

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


What are Energy Levels?

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


What is the Emission Line Spectrum?

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


What is an Absorption Spectrum?

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


What is a Transmission Diffraction Grating?

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


What are Maxima?

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


What is Wein’s Displacement Law?

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


What is Stefan’s Law?

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


What is Luminosity?

The total energy that a star emits per second


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

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


What is a Parsec?

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


What is Stellar Parallax?

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


What is a Light-Year?

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


What is the Doppler Effect?

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


What is Red Shift?

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


What is Hubble’s Law?

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


What is the Hubble Constant?

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


What is Cosmic Microwave Background Radiation?

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


What is the Big Bang Theory?

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


What is the Cosmological Principle?

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)


What is Dark Matter?

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


What is Dark Energy?

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