Astrophysics and Cosmology Flashcards
(44 cards)
What is one Astronomical Unit (AU)?
The mean distance between the sun and the earth
What is nuclear fusion?
The process of two nuclei joining together and releasing energy from a change in binding energy
What is a light year?
The distance that it takes one year for light to travel
What is a parsec?
The distance at which the mean radius of the earth’s orbit subtends an angle of one second of arc.
What is the distance to a nearby star given by in terms of parsecs?
d (distance in parsecs) = 1 / p (parallax in arcseconds)
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 gradual 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 star’s own mass.
What is radiation pressure?
Pressure acting outwards due to the momentum of photons released in fusion reactions.
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.
What is a red giant?
A star in the later stages of its life, that has nearly exhausted all the hydrogen in its core and is now fusing with helium nuclei. It is bigger than a normal star because its 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 luminosity.
What is a planetary nebula?
An expanding glowing shell of ionised hydrogen and helium ejected from a red giant at the end of its life.
What is electron degeneracy pressure?
The pressure that stops the gravitational collapse of a low-mass star (below the Chandrasekhar limit of 1.4 solar masses), stopping a white dwarf from collapsing.
What is a red super giant?
A star that has exhausted all the hydrogen in its core and has a mass above much higher than the sun.
What is a supernova?
A huge explosion when the core of a red super giant collapses.
What is a 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 the life cycle of a low-mass star?
stellar nebula -> main sequence star -> red giant -> planetary nebula -> white dwarf
What is the life cycle of a high-mass star?
stellar nebula -> massive star -> red super giant -> supernova -> black hole/neutron star
What is a neutron star?
The remains of the core of a red super giant after it has undergone a supernova explosion. It is extremely dense and composed of mainly 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 small with a gravitational field so strong that light can’t escape.
What is the luminosity of a star?
The total energy the star emits per second.
What does the Hertzsprung-Russel diagram show?
This shows the positions of stars on a scatter graph based on their luminosities and their temperatures and temperatures.
What is a continuous spectrum?
The spectrum that appears to contain all wavelengths over a comparatively wide range.
What are energy levels?
They are the specific energies that electrons can have when occupying certain orbits. Electrons can only occupy these discrete energy levels and cannot exist at other energy values between them.
What is an emission line spectrum of an element?
The spectrum of frequencies of EM 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.
