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Topic 10/12: Astrophysics and cosmology (Quiz)
Terms in this set (36)
What is different between electric and gravitational fields?
Unlike electric fields, gravity is always attractive.
What is the value of g on Earth?
How are stars formed?
From interstellar gas clouds by nuclear fusion
Is gravitational force as gravity attractive, repulsive or both?
What is a radial field?
field lines directly towards/away from point charge
How are field strength and the object related?
The field strength is independent of the object being acted upon
What is the area under a blackbody radiation curve equal to?
The area under the curve = total energy being radiated
The total energy being radiated increases rapidly as the temperature increases (Stefan-Boltzmann Law).
What do the EM emissions of stars give us information about?
temperature, chemical composition, speed of movement, approximate age, size and much more
What does luminosity depend on?
Size and temperature
What is the peak EM radiation wavelength emitted by the Sun?
What are the star classes (in order from hottest to coldest)?
O B A F G K M
What is a mnemonic for the star classes?
Oh, Be A Fine Guy, Kiss Me! (hottest to coldest)
What colour are supergiants?
blue - generally O class stars
What is the Hertzsprung-Russell diagram?
A plot of star temperatures against luminosity that shows a general negative correlation
Assumption: star behaves as a black body
Which part of the Hertzsprung-Russell diagram do most observed stars fall into?
the 'main sequence' - these are stable stars that will exist in this state for the majority of their lifetime
What element is most of the material in the universe made up of?
Hydrogen - 78%
Helium - 21%
What is a protostar?
sphere of gas after collapse from an interstellar cloud but before nuclear reactions have begun
this star goes through a number of stages ending as a white dwarf, neutron star or black hole
Does nuclear fusion release or absorb energy?
Nuclear fusion releases energy, often as EM radiation
How is a forming star prevented from collapsing under gravitational force?
A star is prevented from collapsing under gravitational force by:
- the pressure from the vibration of its particles
- the EM radiation trying to escape
How is the evolution of a star driven?
By the battle between the outward pressure and gravity
It depends on the initial mass of the star - changes which life cycle a star follows
What are the two main life cycles for stars?
protostar → Sun-like star → red giant → planetary nebula → white dwarf
protostar → blue supergiant → red giant → type II supernova → black hole OR neutron star
What is a neutron star?
Remains of a supernova that have an extremely dense, solid core
it is as dense as nucleons in an atom's nucleus
can hold 3x the mass of the Sun, but only around 10km in diameter
What is the value of one astronomical unit in metres, m?
1AU = 1.5 x 10^11m
What is the value of 1 parsec in light years?
1 parsec = 3.26 light years
What are variable stars?
Stars that have brightnesses changing in repeating cycles with a constant time period, which is directly proportional to the luminosity of each star
What does a longer time period of a variable star suggest?
Longer time period = intrinsically brighter star
What does the width of a spectral line suggest?
the width of spectral lines can be used to determine whether or not it is a main sequence star or not
What is Wien's law?
Wien's Law tells us that objects of different temperature emit spectra that peak at different wavelengths. Hotter objects emit most of their radiation at shorter wavelengths; hence they will appear to be bluer
What is Hubble's law?
The recession velocity of a galaxy is directly proportional to its distance from us.
What is the estimated age of the universe?
13.7 billion years
What does the fate of the universe (whether it will continue expanding) depend on?
- the mass of the Universe
- the density of matter
What could lead to a Big Crunch?
Gravity: the force of gravity between particles decreases with the square of the distance. If the matter is sparse, gravitational forces bewteen particles will be quite weak.
What density must matter have to lead to a Big Crunch?
If the matter has more than the critical density, then the gravitational forces will succeed in causing the Big Crunch
What is dark matter?
Matter that does not give off electromagnetic radiation but is quite abundant in the universe.
What percentage of the universe is dark matter, dark energy and other?
The total mass-energy of the universe contains 4.9% ordinary matter and energy, 26.8% dark matter and 68.3% of an unknown form of energy known as dark energy
Why must we know a star's luminosity in order to determine its distance if it is more than 200 parsecs away?
Trigonometric parallax is no longer reliable.
Luminosity decreases with distance and/or luminosity can vary over time with some stars
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