6. Space physics Flashcards
What happens during nuclear fusion?
Small nuclei fuse together to form larger nuclei
Energy is released and a neutron
Is fusion the energy source for stars?
Yes
What are the similarities between fusion and fission?
both release neutrons
collisions involved
release energy
begin with daughter nuclei
What are differences between fusion and fission?
fission can cause a chain reaction
fusion occurs in stars
fusion is when two nuclei collide, fission is when a nucleus splits
different numbers of neutrons are released (fusion releases only 1 neutron)
fusion is with small nuclei + fission is with large ones
Why is it difficult to fuse two nuclei together?
nuclei are positively charged
What are the conditions required for nuclear fusion?
high temps and high pressures
this mean that the nuclei are moving fast enough to ->
to overcome repulsive forces between (positive) nuclei + force them together
What are the energy transfers in fusion?
energy radiated away from stars is stored as nuclear energy of protons and nuclei in the star
nuclear fusion transfers this into kinetic energy of nuclei (and transferred by radiation)
What is a universe?
Large collection of billions of galaxies
What is a galaxy?
Large collection of billions of stars
What galaxy is our solar system within?
Milky Way
What are asteroids?
small pieces of rocks which orbit the sun between mars and jupiter
What are comets?
Rock / ice / methane / ammonia a few km in diameter
Orbit the sun in highly eccentric ellipses
What are comets?
Rock / ice / methane / ammonia a few km in diameter
Orbit the sun in highly eccentric ellipses
What do gravitational forces do?
cause moons to orbit planets
planets to orbit sun
causes artificial satellites to orbit earth
causes comets to orbit the sun
gravitational force keeps them moving in curved paths (orbits)
Why do comets travel faster when they are closer to the sun?
Gravitational forces are larger when the objects are closer
Farther away from sun - maximum GPE and lower KE
Closer to sun- lower GPE and maximum KE
Describe the differences in the orbits of comets moons and planets?
comets have highly elliptical orbits around the sun
moons have circular orbits
planets have slightly elliptical orbits
What is the orbital speed equation?
Orbital speed = circumference (distance travelled) /orbital period (time to orbit once)
Orbital speed=
2π r (radius is distance from planet to sun) /T
How to convert years to hours?
365 x 24 = 8760 hours
What is meant by spectral class?
letter label given to a star
- relates to its colour and temp
Recite the letters of spectral class, from hottest to coldest
Only
Bats
And
Flies
Go
Kicking
Mice
What colour is the spectral class O and B?
Blue
What colour is the spectral class A and F?
Blue white
White
What colour is the spectral class G?
Yellow white
What colour is the spectral class K?
Orange
What colour is the spectral class M?
Red
Describe the evolution of stars of similar mass to the sun through the following stages:
nebula
star (main sequence)
NEBULA
1. Nebula collapses (dust + gas fall toward centre of mass due to gravitational attraction)
2. GPE -> KE + THERMAL ENERGY of the gas (thus temp increases)
3. Protostar forms at centre (planets form in disk surrounding it)
4. temp in protostar continues to increase until hot enough for nuclear fusion to occur, now main sequence star
MAIN SEQUENCE (stable)
1. When size is not changing= stable
2. Gravitational forces (trying to make star collapse) and thermal pressures (trying to make star expand) are in equilibrium
Describe the evolution of stars of similar mass to the sun through the following stages:
red giant
white dwarf
RED GIANT
1. Runs out of hydrogen -> OuTER SHELL gravitationally collapses, (as gravitational force bigger than thermal pressures) increasing the temp
2. Eventually hot enough for helium fusion to occur - increases temp further -> star expands to become a red giant (red because surface area so large, cooler than before) fusion of heavier elements becomes possible as temp increases
WHITE DWARF
1. Star expands rapidly due to increase in temp (caused by fusion of heavier elements) gravity not strong enough to keep star together -> outer layers of star are ejected (left with core of the star)
2. Star core compresses until it becomes very small hot white dwarf
3. Eventually becomes black dwarf when it radiates all of its energy
Do high or low mass stars have a larger lifetime? Why?
Low mass as fusion occurs more slowly (not as hot)
Describe the evolution of stars with a mass larger than the sun?
Red SUper giant and supernova
RED SUPER GIANT
1. After stable period, larger mass stars expand into red supergiants
2. Fusion can occur up to creation of iron.
SUPERNOVA
3. Runs out of nuclear fuel -> rapid collapse of star (temperature decreases, gravitational forces overcome outward pressure)
4. Followed by an explosion (enough GPE transferred to fuse elements heavier than iron)
5. Material ejected by supernova spreads out into space in a nebula (where more stars are born - these with heavier elements)
Scientists believe that the universe began in the Big Bang. It predicts that most of the universe would be hydrogen with small amounts of heavier elements. Explain where the other elements were created?
Elements < iron but > hydrogen occurred in centre of stars by fusion
Energy released in supernova enough to create elements > iron
Describe the evolution of stars with a mass larger than the sun. Neutron star and black holes
NEUTRON STARS
one remnant of supernova = neutron star = small and dense
Black holes
if remnant is greater than 2.5 solar masses a black hole remains
black hole so dense that light cannot escape its gravitational field
Describe large mass main sequence stars
Hot
White + blue
Fusion occurs quickly
Relatively short lifetime
Low mass main sequence stars
Cool
Red
Fusion occurs slowly
Large lifetime
What is apparent magnitude?
Brightness of a star
depends on : luminosity (how much energy it radiates) + distance from Earth
very bright = small/negative apparent magnitudes
very dim = high apparent magnitudes
What is absolute magnitude?
allows us to compare brightness of stars -> measure of how bright they would appear if all same distance from earth (only depends on luminosity)
again, lowest magnitude highest brightness
Why do we see fewer stars in top left and bottom right of HR diagram?
Top left = large mass main sequence stars -> short lifetime -> evolved into red giants -> so few here at one time
Bottom right low mass stars , lower luminosity, very faint + less detected
How will the absolute magnitude of a star alter when it becomes a red giant?
decrease
- larger radius + larger sa so will transfer more energy
How can you deduce the relative ages of galaxies from HR diagrams?
HR diagram showing only ms stars indicates younger galaxy than one showing less main sequence stars, and more red giant etc stars
enough time has passed for a ms to turn into an rg or a wd
Describe the past evolution of the universe
Universe started 13.8 billion years ago with Big Bang
universe expanded from sate of high density + temp
as universe expanded universe cooled + decreased in density
as it cooled atoms, molecules, stars + galaxies formed
What is CMBR radiation and how does it support the Big Bang theory?
cosmic microwave background radiation emitted during Big Bang
emitted as gamma radiation
wavelength stretched because universe is expanding
microwave radiation present everywhere leftover from Big Bang, which implies all parts of the universe were in contact a long time ago
If a galaxy is moving towards us, how would you expect the frequency of light to change?
frequency will increase (blue shift)
If a a galaxy is moving away from us, how would you expect the frequency of light to change?
Frequency will decrease (red shift)
If a a galaxy is moving away from us, how would you expect the frequency of light to change?
Frequency will decrease (red shift)
How does red shift of galaxies support the Big Bang theory?
the further the galaxy is from earth, the greater the red shift
the greater the red shift, the faster the galaxy is moving away
speed of galaxies increases with increased distance
relationship between speed and distance implies expansion from a single point or since Big Bang
What is the Doppler effect?
when moving away from observer, apparent wavelength increases, decrease in frequency
when moving towards observer, wavelength decreases, frequency increases
wave speed is constant
Do furthest galaxies move away from us faster?
Yes, they have more red shift
The Doppler Effect
The change of wavelength (and frequency) of the waves from a moving source depending on whether they are in front of or behind the observer.
How does a sound change when the source is moving towards you?
> The sound waves get compressed.
The wavelengths get more frequent.
The pitch is higher.
How does a sound change when the source is moving away from you?
> The sound waves get spread out.
The wavelengths get less frequent.
The pitch is lower.
Red Shift
> When an object is moving away from us.
The wavelengths get more spread out.
This causes the spectrum of light to shift to the red side.
Blue Shift
> When an object is moving towards us.
The wavelengths get more squashed together.
This causes the spectrum of light to shift to the blue side.
The faster a star or galaxy is moving (relative to us) …
… The larger the red/blue shift.