Space Physics Flashcards
What type of star is our star classed as?
- Main sequence star
- dwarf star
What is the mass of out sun?
1 Solar Mass (2 x 10^30)
What is the typical mass of a star?
One greater than that of 1 Solar Mass (1M)
Where does fusion occur in the star?
the core only
What is the only type of fusion in a star?
Hydrogen to helium
What are located on the sun, in parts where it is cooler?
Sun spots
What are the layers of the sun (outer to innermost)?
Corona, chromosphere, photosphere with convection zone and core
What can be seen coming off the outside of the chromosphere?
Prominence
What is the temperature of the core of a main sequence star?
15 million Kelvin
What is the temperature of the photosphere of a main sequence star?
5,700 Kelvin
What is the visible part of a main sequence star?
Photosphere
What is found in the radiative zone?
Metal ions
What is found in the convection zone?
Atoms of helium and hydrogen
What is dust?
Any atoms or molecules that are not helium or hydrogen
Describe the formation of a main sequence star:
- Large mass of gas and dust begin to collapse gravitationally due to non-uniform density
- Transfer of g.p.e to k.e. results in an increase of temperature at the centre of the cloud
- When temperature is high enough, thermonuclear fusion initiates; hydrogen nuclei fuse together to form Helium nuclei
- After some time, an equilibrium is established between the continued gravitational collapse and the radiation pressure of photons emitted by the core
- A main sequence star is formed
Describe how a red giant is formed from a main sequence solar mass star:
- Hydrogen in core is exhausted
- Fusion ceases
- Radiation pressure is lost
- So equilibrium between gravitational collapse and radiation pressure is lost
- The core collapses
- G.P.E is converted into kinetic energy so temperature of the core increases
- Temperature is then sufficient for Helium fusion to initiate
- Increased temperature of core creates greater radiation pressure- star expands
- A red giant is formed
Describe the key features of a Red Giant:
- cooler surface than a main sequence star
- more luminous due to increased surface area
What is the composition of a white dwarf core?
Diamond
Describe how a red giant evolves further to a white dwarf:
- Helium in the core is exhausted
- Fusion ceases
- Radiation pressure is lost
- Equilibrium between gravitational collapse and radiation pressure is lost
- Core collapses
- G.P.E is converted into K.E. so the temperature of the core increases
- However, temperature is insufficient for carbon fusion to initiate
- Core continues to collapse until new equilibrium is established between gravitational collpase and electron pressure
- Outer layers of the star are ‘left behind’ to form a planetary nebula
- remaining mass is known as a white dwarf
Describe the key features of a white dwarf:
- denisty a million times greater than a main sequence star
- radius 100 times smaller than main sequence star (7000km)
- surface temperature around 100,000K compared to 1000K for main sequence star
- very low luminosity due to very small surface area
Describe the process at the end of the life of a star with a mass greater than 8 solar masses:
- After a long sequence of fusion events, the core of the star ends up as iron
- Iron fusion is endothermic
- The energy for iron fusion comes from the layers of the star outside the core
- All the star’s energy pours into the core in a fraction of a second
- A supernova explosion occurs
What could the result objects be of a supernova?
- Neutron Star
- Black Hole
What is the mass of a Neutron star supernova remnant?
1.5 solar masses
What is the mass of a black hole supernova remnant?
2.5 solar masses
What prevents further collapse in a neutron star?
The strong nuclear force
What is a neutron star made of? Why?
Made of neutrons - all the protons absorb electrons during the supernova and turn into neutrons
What is the density of a neutron star like?
Millions of times greater than normal matter
What is formed with a black hole?
A point of infinite density (singularity)
What orbits a black hole? Why?
An accretion disc orbits the black hole, created by the gravitational pull
What are the key properties of a neutron star?
- Rotates very rapidly
- Has very strong magnetic fields
- Produces very strong beams of radiowaves
- Radiowaves beam out across space
Why do neutron stars produce beams of radiowaves?
Due to electrons interacting with the magnetic field
What happens when a beam from a neutron star coincides with our line of sight?
We observe radio pulses - Pulsars
What is the event horizon of a black hole?
The distance from the singularity at which the escape velocity is equal to the speed of light
What do fusion processes in stars produce?
All the naturally occuring elements
What elements are produced in a supernova?
Elements heavier than iron
How are elements distributed throughout the universe?
Through the explosion of a massive star (supernova)
What is cosmology?
The study of the universe on the largest scale
Why is the bang bang theory the most widely accepted theory for the origin of the universe?
- It is the best supported by observational evidence
- Evidence, in the form of data collected from electromagnetic waves using telescopes, has been shown to be repeatable and undergone thorough peer review
What does the big bang theory suggest?
- All the mass and energy now present in the universe once existed at a single point
- This point underwent very rapid expansion (strictly inflation followed by expansion)
- As the energy spread out over this larger volume, it ‘cooled’ ; condensing into matter
- First into fundamental particles (electrons and quarks), then into protons and neutrons (three quakrs bound together), then into nuclei and atoms
- stars eventually formed from atoms via gravitational collapse
- because of the very high density of matter, all the stars were supergiants, some collapsed on formation to form supermassive black holes
- around which stars became gravitationally bound, creating galaxies
What is the evidence to support the Big Bang Theory?
- Cosmological Red Shift
- cosmic microwave bakground radiation
What is cosmological red shift?
- the light from distant galaxies is observed at a longer wavelength than would be observed from a stationary source
- this implies that galaxies are moving away from us, the observers
How does Red shift support the big bang theory?
- galaxies are receding so in the past they must have been closer to us
- more distant galaxies move faster and the further away the galaxy, the greater the Red shift
- evidence universe is expanding and that in the past far enough, everything muct have started from one point
- Big Bang theory propoeses the Universe began at a single point and expanded
- thus the red-shift is consistent with the orgin of the universe as suggested by the big bang theory
Who discovered cosmic microwave background radiation?
Penzias and Wilson
What did Penzias and Wilson measure?
A 2.7 kelvin microwave background in all directions consistent with a hot big bang
How does cosmic microwave background radiation support the big bang theory?
- Very high frequenct waves were generated by th ehot big bang and have been stretched by the expansion of space time
- we now observe the waves stretched to the wavelength of microwaves (low frequency, low energy)
What does dark mean?
Cannot be detected directly - doesn’t produce or interact with electromagnetic radiation
What is the indirect evidence for dark matter?
there is not sufficient observable matter in galaxies to provide the gravitational force to keep them together
What is the indirect evidence for dark energy?
Observations of supernovae that are spreading at an increasing rate rather than slowing down. The increased rate of expansion has been observed in all direction; the expansion of the universe is speeding up rather than slowing down as predicted by applying gravitational force. There must be energy driving that expansion but we can’t detect its source
What type of motion do orbiting objects in the universe exhibit?
Circular or eliptical periodic motion
What does periodic motion mean?
Means that the orbiting object covers the same path in equal time periods
What is the nature of gravity?
- attractive
- non-contact
How is gravity an attractive force?
since any object with mass will experience a force of attraction from other objects with mass.
How is gravity a non-contact force?
Since a non-contact force is a force which acts on an object without coming physically in contact with it, like gravity which confers weight
How are all naturally ocurring elements including and up to iron created in a star:
- the core of the star is at a very high temperature
- allowing hydrogen nuclei to undergo fusion
- helium nuclei are formed
- later in the star’s life, all the hydrogen in the core has been used up
- so helium nuclei can undergo fusion to produce larger, heavier elements up to iron
- the more massive the star, the hotter its core, so heavier elements up to iron are produced
Describe the process by which a white dwarf is formed and how it becomes a black dwarf:
- Red Giant’s core collapses under gravity and the loss of radiation pressure
- The outer layers of the star are left behind/blown away
- This leaves a much smaller, denser core
- this core’s temperature rises due to the compression due to gravity and it glows much brighter
- it cannot further generate energy by nuclear fusion
- cools and dims as time passes
- it is descrbed as a black dwarf when it stops emitting energy/radiation
What is the relevance of speed in orbits?
- to maintain a stable orbit at a specific radius, the speed must have a particular value
- if the speed is not correct, the radius of the orbit will change
Why is observing very distant galaxies like looking backin time?
- The light from the distant objects has been travelling for a very long time
- therefore the light detected was emitted from the object a very long time ago
What does gravity cause?
massive objects to accelerate
What does the acceleration due to gravity manifest in?
A force experienced by the massive object
How does a gravitationally driven orbit keep in circular motion?
Because both the acceleration due to gravity and force act towards the centre of the circular path - centripetal
What does the magnitude of the centripetal force required to keep a massive body in a stable circular path depend on?
- the mass of the moving body
- the speed of the body
- the radius of the path
What is the relationship between the magnitude of the centripetal force of a stable orbit and what it depends on?
- it is proportional to mass and speed squared (large mass/speed = big force)
- it is inversely proportional to radius (ie. big radius = small force)
What is the releationship between the speed and radius of a stable orbit and the mass of the orbiting body?Under what conditions?
Where the centripetal force results from gravity, the speed and radius of a stable orbit are independent of the mass of the orbiting body
Why are protostars hot?
As the star gets compressed by the gravitational forces, it gets denser, the particles speed up and collide more, this raises the internal temperature of the star
Why is it difficult to detect protostars with telescopes from the Earth’s surface?
The protostars are dim/faint, they only produce infrared radiation which cannot penetrate our atmosphere
What will be observed if a distant star goes supernova?
the star will be much brighter for a peroid of several days or weeks, which would be observed on Earth many years later (ie. distance in light years)
Do planets take longer or slower to orbit a star if they are further away from it? why?
Longer since the further away the plaent/object from the body it orbits, the slower it travels
Why do moons follow circular paths?
- each moon experiences a centripetal force produced by gravity
- this accelerates the moon constantly towards the planet
- since the acceleration is perpendicular to the moon’s movement, it will cause a change in the direction but no change in speed of the moon
- the moon is constantly pulling towards the planet, resulting in a circular path with the planet at the centre
Why can geostationary communication satellites not be placed at a lower height to reduce signal delay?
at closer distances to the Earth, the satellite would need to travel at a higher speed to orbit the Earth. It would complete the revolution in less than 24 hours so would not stay in the same place in the sky
Why was Hubble’s red shift theory initially rejected?
Because the scientists were confident with their previous theory and would require overwhelming evidence to replace it
Why did Hubble’s red shift theory eventually grow to be accepted?
the previous theory ouldn’t explain the observations and sufficiently more evidence was found on the motion of galaxies
What can be used to demonstrate simply the expansion of the universe? How does it demonstrate this? What are the limitations?
- draw galaxies on the surface of a de-flated balloon
- inflate the balloon
- the galaxies on the balloon move awy from all the others, much like the expansion of the universe
- however, the limitiation with a balloon is that the expansion is 2D and not 3D like in reality with universes
