What properties of a star can we determine from its EM emissions?
- Temperature
- Chemical Compositiom
- Size
- Age
- Speed
What is luminosity?
Luminosity is the rate of light energy released / power output of a star
What is the definition and formula of a star’s intensity?
Intensity is the luminosity of a star per unit area. It is inversely proportional to square distance between the star and observer.
I = L/4πd²
What is the definition of parallax?
Parallax is the apparent change in position of a nearer star compared to distant stars.
What are the conditions for trigonometric parallax?
- Only works for nearby stars
- The apparent movement of a nearby star relative to a fixed background
- by taking measurements 6 months apart when earth is at opposite ends
What is the conversion of Astronomical unit to metres?
1 AU = 1.5 x 10¹¹ m
What is the conversion of parsec to light years?
1 Parsec (pc) = 2.06 x 10⁵ AU = 3.08 x 10¹⁶ m = 3.26 ly
What is a standard candle?
A standard candle is an object of known luminosity.
How do you use standard candle to determine astronomical distances?
d² = L/4π x l
What is the stellar evolution for stars <3M☉?
For stars of mass <1.4M☉
1. Main sequence star
2. Protostar
3. Red giant
4. White dwarf
5. Black dwarf
For stars of mass 1.4M☉ - 3M☉:
1.Protostar
2. Main sequence star
3. Red giant
4. Supernova
5. Neutron Star or Black Hole
What is the stellar evolution for stars of mass >3M☉?
For stars of mass >3M☉:
1. Protostar
2. Main sequence Star
3. Red supergiant
4. Supernova
5. Neutron star or black hole
What are the properties of a protostar?
- Large quantity of mass (mainly hydrogen0 gathering due to gravity attracting it together
- no fusion taking place
What are the properties of a main sequence star?
- Hydrogen fusion takes place
- inward gravitational force is equal to the outward pressure from hydrogen fusion reaction. Forces are balanced.
What are the properties of a red giant?
- Towards end of main sequence, hydrogen fusion stops in the core and collapses.
- Temperature is high enough to fuse helium into heavier elements.
What are the properties of a white dwarf?
- Fusion stops as star can no longer fuse heavier elements together.
- No outward force due to no fusion so the star collapses under its own gravity and becomes white dwarf
- Stars temperature increases as it contracts inwards and continues to glow as a white dwarf.
-Temp not hot enough for heavier elements
What are the properties of a black dwarf?
When the star cools down, it settles as a black dwarf.
What are the properties of a red supergiant?
When a high mass star runs out of nuclei, the same process for red giant occurs but on a larger scale.
What are the properties supernova?
- When all fuel runs out, fusion stops and the core collapses inwards and becomes rigid.
- Outer layers of star fall inwards and rebound off the core launching them out into space in a shockwave.
- As the shockwave passes through surrounding ,aterial, elements heavier than iron are fused and flung into space
What are the properties of a neutron star?
- When the core of a large star collapses, gravity is so strong, it forces protons and electrons together to form neutrons.
What are the properties of a black hole?
When the core of a giant star collapses, the neutrons are unable to withstand gravity forcing them together.
What is the doppler effect?
Apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer.
As the source is moving, the wavelengths in front of it are compressed and the wavelengths behind are spread out. Similar to sound of car moving past you.
What is red-shift?
Red shift happens when a star moves away from Earth. EM Wavelength observed on Earth is longer than wavelength initially emitted from source (laboratory wavelength).
What is blue-shift?
Blue shift is exhibited when a star moves towards observer. Wavelength observed is shorter than the wavelength initially emitted.
Describe how distances too large for the use of standard candles can be determined
- Measure change in λ/f
- Determine relative velocity using redshift equation
- Use v=H₀d
