Classification of Stars COPY Flashcards
Is absolute magnitude subjective or not?
Not subjective
Where does fusion stop in smaller stars?
Carbon and oxygen
What is the distance in parsecs in terms of the parallax angle?
Distance in parsecs = 1 / parallax angle (arc seconds)
What spectral classes are the Balmer lines dominant?
B & A
Describe the formation of a neutron star
- The stars core is 1.4 times the suns mass
- The quantum effect from the electrons cannot stop it collapsing
- The electrons get pushed onto atomic nuclei and form neutrons and neutrinos
- The core is made of neutrons
- The outer layers continue to collapse until the core cannot be compressed further
- The outer layers rebound off the core
- Causes a supernova
- Only core (neutron star) is left
What is the difference in brightness between two stars one magnitude apart?
2.51
What does the number of electrons in the different energy levels depend on?
Temperature of the gas
How many times brighter is a magnitude 1 star compared to a magnitude 6 star?
100
Define the parsec
The distance to a point in space where the radius of the Earth’s orbit of the Sun subtends an angle of 1 arc second.
How dense are neutron stars?
4 x1017 kgm-3 which is the density of nuclear matter
Define a supernova
Where a giant star explodes at the end of its life. It has a rapid and short-lives increase in absolute magnitude
When is an absorption spectrum formed?
When a continous spectrum of white light is passed through a cool gas
What can the darkness of the Balmer lines be used to determine?
The temperature of the gas - and therefore the spectral class
Define absolute magnitude
What the apparent magnitude would be of the star/galaxy was 10 parsecs away from the sun
How do you go from seconds to degrees?
multiply by 1 / 60
What is the Intensity of a star measured in?
Wm^-2
What is the absolute magnitude of the sun?
+4.77
Define what is meant by ‘the intensity of radiation hitting Earth from a star’
The energy each second from the star hitting 1 square metre on earth at right angles.
What is the equation for Weins Law?
When does a star turn into a white dwarf?
ONLY THE CORE OF THE STAR
at the end of their life (after red giant stage)
What is a main sequence star?
Where the star goes into an equilibrium state, where it will stay for many millions of years, until the hydrogen in the core runs out.
What are the most energetic event in the universe?
When burst of high energy gamma rays are emitted when they supernova
They usually last minutes but can last hours
What is the equation for Stefan’s Law?
Which spectral class are white dwarfs?
O/B
Is apparent magnitude subjective or not?
It is subjective
What is the equation for the schwarzchild radius
R = 2GM / c2
What are the prominent absorption lines linked to each spectral class?
O - He+, He, H
B - He, H
A - H (strongest), ionised metals
F - ionised metals
G - ionised & neutral metals
K - neutral metals
M - neutral atoms, TiO
When does a star begin to turn into a neutron star?
When its core is 1.4 times the sun’s mass
Define the astronomical unit
The mean distance from the Sun to the Earth
What is the equation that links the intensity of a star to the luminosity of the star?
The star Capella is approximately 100 times more luminous than the sun. What is Capellas absolute magnitude?
If its apparent magnitude is measured at 0.08, how far away is it in parsecs?
What can the parallax method only been used on?
Closeby stars
Define the apparent magnitude of a star
It is a measurement of how bright (just visible wavelengths) the star appears to us on Earth. It is subjective in that it depends on how far the observer is from the star
Describe a red giant in terms of luminosity and temperature
High luminosity
Relatively low temperature
What are the spectral classes of stars?
O B A F G K M
Where is the main sequence “saddle” located on a Hertzsprung-Russell diagram?
At an absolute magnitude of around 4
What is the Balmer absorption spectrum?
The visible absorbtion spectrum in hydrogen.
Give four facts about neutron stars
- Very dense (4 x1017 which is the density of nuclear matter)
- Very strong magnetic field
- Spinning neutron star is called a pulsar and is a strong radio source
- Only a few 10’s of metres in diameter
What is a black hole?
An object where the escape velocity is greater than the speed of light
Define the Intensity of a star
The energy each second from the star hitting 1m^2 perpendicular to the radiation on Earth.
what does the equation that links intensity and luminosity assume?
Energy is not lost / no radiation is sbsorbed or scattered
Draw the Hertzsprung-Russell diagram
What is an emission spectrum given off by?
Hot gases
Gases with an electric field passed through it
Why is the equation for the Schwarzchild radius only approximate?
Newton’s gravitational equations do not work in intense gravitational fields
How do you go from seconds to arc seconds?
Multiply by 60
How do you go from arc seconds to degrees?
multiply by 1 / 3600
What are the axis on the Hertzsprung-Russell diagram?
Temperature: 50 000 - 2 500
Absolute Magnitude: -10 - 15
What are standard candles?
Objects in the sky whose absolute magnitude are known
What is a continous spectrum given off by?
Hot solids
What is the event horizon?
The boundary of the black hole, where the escape velocity is the speed of light
What is spectral class and temperature of the sun?
G2
5 800K
What are cephid variables?
Stars which grow brighter and dimmer over a number of days
Alinam is 1350 light years from Earth. It has an apparent magnitude of 1.7. What is its absolute magnitude?
What is the life cycle of a very large star?
Main sequence, giant, supergiant, supoernova, black hole/neutron star
Define the Luminosity of a star
The total amount of electromagnetic radiation it emits each second, measured in J/s or W. It is the power of the star
What is the surface area of a sphere?
What is a white dwarf?
The core of a star, which is very hot and with a small diameter.
What is the stuff you need to know about the sun?
(Temp, Absolute magnitude, Spectral class)
- Temp: 5 800
- Absolute magnitude: +4.77
- Spectral class: G2
Define light year
The distance that light travels in a year
What are quasars?
Supermassive black holes at the centre of galaxies which are very strong emitters of radio waves
What is the highest absolute magnitude (brightest value) on a Hertzsprung-Russell diagram?
-10
Where does the visible absorption spectrum in hydrogen come from?
The electrons in the n=2 level abrosbing photons
Why is an absorption spectrum seen when the spectrum from a galaxy or star is viewed?
Light from stars is emitted from the hot centre of the star and then passes through cooler gases neaar to the surface of the star.
Some wavelengths are absorbed by the cooler gases.
When do stars become red giants?
As they come to the end of their lives adter they have been on main sequence
What colour is linked to each spectral class?
O - Blue
B - Blue
A - Blue-white
F - white
G - yellow-white
K - orange
M - red
Why do stars obey Weins Law?
They are black bodies
What is rthe Schwarzchild radius?
The distance between the centre of the black hole
Define a black body
A black body completely absorbs all wavelengths of radiation falling on it and can all wavelengths
What temperatures are linked to each spectral class?
O - 25 000 - 50 000
B - 11 000 - 25 000
A - 7 500 - 11 000
F - 6 000 - 7 500
G - 5 000 - 6 000
K - 3 500 - 5 000
M - <3 500
What is the link between the distance from a star and the intensity of the star?
There is an inverse square relationship (distance doubles, the intensity quarters)
Draw the Hertzsprung-Russell diagram to show the stellar evolution of the sun / a star similar to the sun
Where does the fusion stop for very large stars?
Iron
Draw a black body curve for an object that has a maximum wavelength of 250nm
What is the energy output of a type 1a supernova?
1044J
This is similar to the energy given out by the sun in its lifetime
