Classification Of Stars Flashcards
What is luminosity?
The rate of energy released by a star.
(Power output of a star)
What is intensity (astrophysics)?
The power received from a star per unit area.
What is apparent magnitude?
How bright an object appears in the sky from Earth.
What is absolute magnitude?
The brightness of an object when viewed from 10 parsecs away.
How does parallax affect viewing stars?
As the Earth orbits the sun and views stars at different points it can look like the star has moved.
This is measured as the angle of parallax (θ). The greater the angle the closer the star to Earth.
What is 1 AU?
The average distance between the centre of the Earth and the centre of the sun.
What is a parsec?
The distance at which 1 AU subtends an angle of 1 arcsecond.
How do you calculate distance from an object (parsecs) using angle of parallax?
d = 1/θ
d is in parsecs, θ is in radians
What is a black body/black body radiator?
A perfect emitter and absorber of all possible wavelengths of radiation.
What is Stefan’s Law?
The power output of a black body radiator is directly proportional to its surface area and its (absolute temperature)⁴
What is power output of a black body equation?
P = σAT⁴
What is Wien’s Displacement Law?
The peak wavelength of emitted radiation is inversely proportional to the absolute temperature of the black body.
How can intensity of a star be calculated?
I = P/4πd²
What are the Spectral Classes of stars? (Highest-Lowest Temperature)
O B A F G K M
What colour are stars of spectral class O?
Blue
What colour are stars of spectral class B?
Blue
What colour are stars of spectral class A?
Blue/White
What colour are stars of spectral class F?
White
What colour are stars of spectral class G?
Yellow/White
What colour are stars of spectral class K?
Orange
What colour are stars of spectral class M?
Red
Which spectral classes produce Hydrogen-Balmer Lines?
O (Prominence = Weakest)
B (Prominence = Weak)
A (Prominence = Strongest)
What is the life-cycle of a star?
Nebula
Protostar
Main Sequence
Red giant (< 3 solar masses) or Red supergiant (> 3 solar masses)
If red giant (< 1.4 solar masses):
White dwarf
Black dwarf
If red giant (>1.4 solar masses) or supergiant:
Supernova
Neutron Star (< 3 solar masses) or black hole (> 3 solar masses)
What is a nebula (understanding)?
A “cloud” of gas and dust in space.
What is a protostar (understanding)?
Fragments of nebula clump together under gravity.
Irregular clumps rotate and spin towards a denser centre (protostar) under gravity.
Protostar is surrounded by circumstellar disc.
Once hot, fuses small elements, producing a stellar wind that blows away surrounding material.
What is a main sequence star (understanding)?
Inward force and outward force of gravity and fusion are in equilibrium.
Hydrogen is fused into helium.
Larger mass = shorter main sequence period.
What is a red giant star (understanding)?
< 3 solar masses.
Once hydrogen runs out, temperature of core increases.
Core fuses larger elements (carbon, oxygen, beryllium etc.)
Outer layers of the star expand and cool.
What is a white dwarf (understanding)?
< 1.4 solar masses
Red giant used up all fuel, fusion stops.
Core contracts as gravity greater than outward force.
What is a red supergiant (understanding)?
> 3 solar masses
Red supergiants occur from the same process as red giants on a larger scale.
They can fuse elements up to iron.
When they collapse there is always a supernova.
What is a supernova (understanding)?
> 1.4 solar masses
Fusion in star stops and core collapses suddenly and becomes rigid.
Outer layers of star fall inward and rebound of core creating a shockwave.
In this shockwave elements heavier than iron are fused.
Supernovas have rapidly increasing absolute magnitude and release 10⁴⁴J of energy.
What is a neutron star (understanding)?
1.4 - 3 solar masses
When core collapses, gravity is so strong protons and electrons are forced together to form neutrons.
Incredibly dense 10¹⁷kgm⁻³.
Pulsars are spinning neutron stars that emit beams of radiation.
What is a black hole (understanding)?
> 3 solar masses
Core of giant star collapses.
Neutrons unable to withstand gravity forcing them together.
Gravitational pull is so strong not even light can escape.
What is a black hole (PPQ)?
An object with escape velocity greater than the speed of light.
What is the event horizon of a black hole?
The point at which the escape velocity becomes greater than the speed of light.
What is the Schwarzschild radius?
Radius of event horizon.
Rₛ = 2GM/c²
What is a binary system?
Where two stars orbit a common mass.
What is a Type I supernova?
When a star accumulates matter from its companion star in a binary system and explodes after reaching a critical mass.
What is a Type II supernova?
The death of high mass star after it runs out of fuel.
What is a Type Ia supernova?
It is a Type I supernova with a white dwarf.
White dwarf accumulate mass from companion star until reaching critical mass where white dwarf explodes.
What is the (average) peak absolute magnitude of a supernova?
-19.3
What is a standard candle?
An object with known absolute magnitude.
What is the relation between black holes, quasars and galaxies?
Quasar are produce by (supermassive) black holes.
These black holes are at the centre of active galaxies.
Why could evolution of supergiant star be dangerous for life on Earth?
Star could produce a neutron star after collapsing which could then produce γ bursts.
These bursts could then kill cells.
What’s the temperature range of Spectral Class O?
25,000K - 50,000K
What’s the temperature range of Spectral Class B?
11,000K - 25,000K
What’s the temperature range of Spectral Class A?
7,500K - 11,000K
What’s the temperature range of Spectral Class F?
6,000K - 7,500K
What’s the temperature range of Spectral Class G?
5,000K - 6,000K
What’s the temperature range of Spectral Class K?
3,500K - 5,000K
What’s the temperature range of Spectral Class M?
< 3,500K
What’s a (suitable) range of absolute magnitude scale on a Hertzsprung-Russell Diagram?
+15 to -10
What is the Temperature and absolute magnitude of the Sun?
~ 5,800K
~ +5
What are the two key features of a neutron star?
Extremely dense.
Made up of neutrons
