Space Flashcards
What is a black body radiator?
A theoretical that is a perfect absorber and emitter of radiation. All radiation emitted is due to the body’s temperature. We assume stars behave as black bodies
What is the Stefan-Boltzmann law?
The output power of a black body is proportional to the surface area and T^4
L = σAT^4 (luminosity = constant x area x temperature)
What is Wien’s law?
For a black body, the wavelength at which the radiation intensity curve peaks (λmax) is inversely proportional to the Kelvin temperature of the surface
Tλmax = 2.898 x10^-3
How can we accurately identify brightness?
Use the star’s output power, known as luminosity (L)
What affects the brightness of a star we see?
The size of the star, the type of star, the distance from Earth
What are the key points of the intensity against wavelength graph?
- As temperature increases, peak wavelength decreases (and frequency increases)
- The area under the curve represents total luminosity
- Visible radiation is the only part of the spectrum emitted
- Low temperature stars are red
- High temperature stars are blue
What are the initial steps to form any main sequence star?
A large cloud of hydrogen gas and dust known as a nebula collapses over time (due to gravity). The molecules collide, kinetic energy increases so the temperature also increases, leading to the formation of a protostar.
Eventually, the temperature gets so high that nuclear fusion takes place and a star is born. Inside the star hydrogen nuclei fuse together to make helium, a process by which mass is turned into energy which fuels the star
What happens to an average star once the supply of hydrogen begins to run out?
The star becomes unstable and begins to collapse, increasing the temperature further so that helium starts to fuse to make heavier elements. The star then swells up to make a red giant.
When the helium runs out, it collapses into a white dwarf which is very hot. Eventually, this cools down to become a dark, cold star known as a black dwarf
What happens to a very large star once the supply of hydrogen begins to run out?
They can grow into a red super giant once helium begins to fuse to make heavier elements, and the temperature in these becomes so hot that heavier elements can be made in the fusion process.
When the fuel runs out, the star collapses then explodes as a supernova, which then either collapses into a neutron star which is only a few km across, or it may collapse to a microscopic point and form a black hole (which is so dense that nothing can escape from it)
What are the axis of the Hertzsprung-Russel diagram?
The y axis has luminosity in watts (to powers of 10 - logarithmic, which is 1,000,000 at its highest and 0.000001 at its lowest) and magnitude, the x axis has temperature in K (highest at the left of the axis with 20000 just offset from the left and 2500 at the bottom)
What are the spectral classes and how are they grouped?
There are 8 spectral classes which are grouped according to temperature, O, B, A, F, G, K, M
What are the 3 main branches of the Hertzsprung-Russel diagram?
Main sequence stars (the centre), giant and supergiant stars (upper right), white dwarves (bottom left)
What are the key characteristics of main sequence stars?
They are all generating energy by fusing hydrogen to helium. They have the greatest range of brightness, with the brightest stars having a surface temperature of 50,000K and the dullest 2500K, and can be a million times brighter than the sun or 10,000 times duller
What are the key characteristics of giant and super giant stars?
These stars can be relatively cool , with temperatures of 3000K, but they are very bright because they are very large. In these stars, energy is generated by fusion of helium and larger nuclei
What are the key characteristics of white dwarf stars?
Very hot surfaces but they are relatively dull because they are so small. These stars are at the end of their lives; nuclear fusion has stopped, the stars have collapsed and are now cooling down
