IB Physics Option D Astrophysics

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Small rocky body that drifts around the solar system
Asteroid on a collision course with another planet
Mixtures of rocks and ice in very elliptical orbits around the Sun
Cloud of gas and dust where stars begin to form
Binary stars
Two or more stars orbiting around their common centre of mass
Visual binary stars
Can be distinguished using a telescope
Spectroscopic binary stars
As one star approaches Earth, the other recedes
A large number of stars held together in a group by gravitational attraction
Stellar clusters
Stars formed around the same time in the same the region probably from the same nebula
Open clusters
Up to several 100 stars, younger than 10 billion years
Group of stars that form a recognisable pattern that are not gravitationally bound together
Light year
Distance light travels in one year
Astronomical unit
Mean distance between the Earth and the Sun
Total power emitted by the star
Apparent brightness
Incident power per unit area received at the surface of the earth
Line of length 1 astronomical unit subtends an angle of 1 arcsecond at this distance
Cepheid variables
Extremely luminous stars that undergo regular and predictable changes in luminosity
Main sequence stars
Produce energy from fusion of hydrogen, helium and carbon, among other nuclei (~ 90% of stars)
Red giants
Cooler than main sequence stars and emit less energy per square metre but are more luminous, with a greater surface area and diameter
Chandrasekar limit (small stars)
White dwarves cannot have a mass greater than 1.4 * the mass of the Sun
Oppenheimer-Volkoff limit (large stars)
For neutron stars between 1.5 and 3 solar masses, the neutron degeneracy pressure can resist the collapse into a black hole
Redshift (can be Doppler or cosmological/Hubble)
Optical (absorption) spectra moved towards the red end of the EM spectrum
Doppler redshift
A body moving away from an observer
Cosmological (Hubble) redshift
Due to the stretching of space itself leading to stretched wavelengths
Jeans criterion
Magnitude of the (gravitational) potential energy of the gas must be greater than the kinetic energy of the gas (depends on the temperature and particle density in the gas cloud)
Production of different nuclides by the fusion of nuclei
Slow neutron capture (producing nuclides up to Bi-209) – small neutron flux, in massive stars
Rapid neutron capture (producing nuclides heavier than Bi-209) – strong neutron flux, in supernovae
Type I supernovae
No hydrogen line, evolved from old, low-mass stars
Type II supernovae
Hydrogen line present, evolved from young, massive stars.
(Consist of single massive stars in the final stages of their evolution)
Type Ia supernovae
Result from accretion of matter between two stars in a binary star
Standard candles – all have same peak luminosity as they are formed when mass reaches Chandrasekar limit. Measure apparent brightness and calculate distance
Assumptions of Cosmological Principle
Universe is homogeneous and isotropic
Closed universe
Density of universe greater than critical density
Open universe
Density of universe less than critical density
Flat universe
Density of universe equal to critical density
Massive compact halo objects: high density stars, hidden as they are far away from any luminous object – black holes, neutron stars, black dwarfs
Weakly interacting massive particles; non-baryonic subatomic particles, weakly interacting with baryonic matter; need huge quantities to make up dark matter
Minute temperature fluctuations in the CMB
Standard candles
Objects of known luminosity
Redshift ratio (z)
A measure of cosmological redshift
the redshift of a wavelength
the wavelength measured at rest on Earth
Original size of the universe
Current size of the universe
Categories: Astrophysics