Week 1 - Stars Flashcards
What is apparent brightness (flux)?
How bright the star appears to a detector here on Earth.
Depends on distance.
Formula for energy radiated per unit area per second
Formula to work out total luminosity of star?
Explain how stars form from molecular clouds.
Stars form from an accumulation of gas and dust, which collapses due to gravity.
Explain what are the main observed properties of stars
A star can be defined by five basic characteristics:
- Brightness
- Colour
- Surface temperature
- Size
- Mass
Explain what we can tell from a star’s blackbody curve.
The spectral curve at a specific temperature corresponds to a specific peak wavelength.
As the temperature of the blackbody increases, the peak wavelength decreases (Wien’s Law).
Explain how the atmospheric transmission of light might influence the development of planetary life
The atmosphere only lets in EM radiation within a specific range (what we call visible light, radio & microwave). Sensory organs used for the detection of visible light proved to be a useful evolutionary trait.
Describe why stars have different colours
The color of a star is linked to its surface temperature. The hotter the star, the shorter the wavelength of light it will emit.
Explain how colour and temperature are related
Wien’s law: temperature of an object is inversely proportional to its wavelength. As the temperature increases, the wavelength decreases.
Colour depends on wavelength.
Explain what stellar spectral class can tell us about stars.
Spectral types and sub-classes represent a temperature sequence, from hotter (O stars) to cooler (M stars), and from hotter (subclass 0) to cooler (subclass 9). The temperature defines the star’s “colour” and surface brightness.
Explain what an HR diagram is.
Hertzsprung–Russell diagram is a scatter plot of stars showing the relationship between the stars’ absolute magnitudes or luminosities versus their stellar classifications or effective temperatures.
Explain what powers the stars.
Stars are powered by nuclear fusion: a nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy.
Explain how stellar lifetime is related to stellar mass.
A star’s mass gives a measure of the amount of “fuel”, and its luminosity gives a measure of the rate at which this “fuel” is consumed by nuclear burning, so a star’s lifetime is proportional to its Mass divided by its Luminosity.
Explain how we determine the range of stellar masses that we consider relevant when searching for life in our Galaxy.
Mmax: Star must live long enough for life to evolve. Too massive means they die too early. Mmax = 2Msun
Mmin: Energy output depends on mass. If too low then not enough energy for liquid water. Mmin = 0.4Msun
Estimate how many stars are there in our Galaxy.
Approximately 100 billion stars.
