astrophysics and cosmology- refined Flashcards
Define what is meant by a comet
a small irregular body of dust, ice and rock, which orbits a star (highly eccentric elliptical orbit)
define Solar system
a planetary system consisting of stars and at least one planet in orbit around it
what is a galaxy
a cluster or many millions of stars, rotating around a point.
what is a planet
bodies which move in either circular or elliptical orbits, around a star to form a solar system
how does a protostar form?
-Gravitational collapse pulls more and more matter together, work is done on the particles, leading to an increase in their kinetic energy, which results in an increase of temperature until some of the denser gas becomes hot enough to glow.
explain the cause of fusion in protostars.
reference to:
-Pressure
-Temperature
-Gravity
-Hydrogen, Helium-4
-gravitational field will begin to attract more matter
- this happens until the temperature and pressure become much greater
-the core will become millions of kelvins
-this causes the kinetic energy to increase and fusion reactions are able to occur
-hydrogen (four protons turn into helium 4) with the production of two gamma photons, two neutrinos and two positrons.
define radiation pressure, and its relation to gas pressure and its relation to gravitational force, within a stable star
radiation pressure is caused by the momentum of the gamma photons released by the fusion reactions, creating an outward pressure on the star.
in a stable star, radiation pressure and gas pressure are equal to the gravitational pressure. at this point the star becomes a main sequence star.
What is the fate of low-mass stars
- main sequence to red giant
-If a star is less than 1.4 solar masses, it will move off the main sequence to become a red giant, before turning into a white dwarf.
-begins with most of the hydrogen nuclei present within the core being fused into helium.
-nuclear fusion stops
-radiation pressure pushing outward stops, gravity collapses the star. collapse leads to an increase in temp due to compression
-large amount of hydrogen surrounding the core, this will become hot and release thermal energy
-these outer layers expand, cool and form a red giant.
What is the fate of low-mass stars
-red giant to white dwarf
- further contraction of the core by gravitational collapse will continue, as temperature continues to rise
-the core becomes hot enough for fusion of helium to take place, producing heavier elements.
-fusion reactions increase radiation pressure
-once fusion cannot continue, star collapses again - the collapse forms a planetary nebula
-the rest of the star continues to collapse and heat up until it can no longer collapse. what is left is a very hot core (White dwarf)
What is the fate of high mass stars
-Larger stars (over chandrasekhar limit) move off the main sequence, they are much brighter than low mass stars
- Cores contract under gravity and form into red super giants.
- core collapses and heats up, further nuclear fusion reactions can occur of heavier elements
-this continues until an iron core builds up. this core then collapses. fate of the red giant depends on whether the iron core is over 1.4 solar masses. it it is greater than this then the electron degeneracy pressure cannot support it and it will then go under gravitational collapse.
Under what conditions are neutron stars formed
the extremely dense collapsed neutron core has remained in tact
Under what conditions are Black Holes formed
when the mass is greater than three to four solar masses.
what is meant by a continuous spectrum
a spectrum which contains all the wavelengths over a comparatively wide range
energy levels
-mention discrete
specific energies which electrons can have when occupying specific orbits. Discrete energy levels, and cannot exist between them
what is meant by a ‘transmission grating’
a glass surface having a very large number of fine parallel grooves, used to produce optical spectra by diffraction of transmitted light.
