Astrophysics Flashcards
What an astronomical unit
A measurement equivalent to 1.5*10^11m (the orbiting distance of the sun and earth)
What is apparent magnitude
The brightness of a star from earth
What is d
The distance from the nearby star and orbiting planet
How can you work out d (unit is parsec)
d (parsec) = AU / Arcsec
What is arcsec used for
The measure of the angle of parallax = 1/3600 degrees
What is 1 parsec in metres and light years
3.08 * 10^16 m
1pc = 3,26 ly
In Hippochus Apparent brightness scale which magnitude is visible to the naked eye
+6.00 (6th magnitude and lower)
What is the multiplier of change for each magnitude
2.51 times
Which apparent magnitude is brighter -26 or +6.0
-26
What is pagson’s law (ratio of intensity)
I2/I1 = 2.51^m1-m2
What is absolute magnitude?
It is equal to the apparent magnitude if it were placed at a distance of 10 parsecs from the earth
What is the equation for the ratio of intensity
I2/I1 = 2.51^m1-m2
What is a black body object
An object that absorbs all wavelengths of electromagnetic radiation and emits all wavelengths of electromagnetic radiation however does not exist in reality
What does the peak wavelength of an object help determine using wiens law?
The temperature
What is Wiens law on temperature
Max wavelength * temperature = weins constant
What is stefans formula
Power output of a star = stefans constant * surface area * temperature^4
What is the equation for intensity of light
intensity = p / 4pi * distance^2
What is luminousity?
The brightness of a star and the rate of light energy released by a star (power output)
Define parsec
The distance when the angle of parallax is 1 arcsec
What determines the luminosity of a star?
The average energy per photon
The amount of photons released per second
What does the colour of a star depend on?
The wavelength of light it does not absorb
In the Balmer series what do the absorption lines indicate?
Highlights any excitation or dexcitation involving n=2 and hydrogen, via visible light only
What are HR diagrams
Absolute magnitude (luminosity) against decreasing temperature (OBAFGKM)
involves main sequence stars, white dwarfs and red giants
What are protostars
These are baby stars formed from nebulas (compression of dust and gas), they’re not a part of the main sequence stars
What defines a star and allows protostars to be a part of the main sequence stars?
- can conduct nuclear fusion
- has a certain amount of mass
- equilibrium of pressure (force from nuclear fusion) and gravity
Why do clouds of dust and gas gather
Due to gravity
What do main sequence stars fuse together for billions of years
Hydrogen into helium
What can main sequence stars become depending on their mass
High mass - red super giants
Low mass - red giants
What do red giants do?
They eventually run out of hydrogen to fuse, as temperature increases they begin to fuse helium to form heavier elements
- their outer layers expand and cool
How are white dwarfs formed?
When red giants are unable to conduct nuclear fusion due to running out of fuel, gravity becomes greater than pressure so the star contracts.
The core becomes dense only emitting light
How are black dwarfs formed
When white dwarfs no longer emit light and are cooled down
What are red super giants
- They also continue to fuse helium atoms when hydrogen atoms however they can make elements up to iron
- bigger than 3 times the solar mass
What are supernovas?
A huge explosion of red super giants that occurs when all fuel runs out and gravity collapses in itself, as the outer layer falls inwards it rebounds of heat core launching them into space in a shockwave
This is where all elements heavier than iron is fused and flung into space
What is a neutron star
When the gravity of a red super giant is so strong that it forces protons and electrons together to form neutrons (it is incredibly dense)
What is black hole
When escape velocity becomes greater than the speed of light, gravity too strong where it forces neutrons to come together.
What are the characteristics of a supernova
- a great explosion of light
- gravity condenses protons and electrons which forces electron capture which forms neutrons
- shockwaves emit material and energy
What is the range of absolute magnitude for supernovas?
-15 to -20
How long do supernovas outshine the whole galaxy
24 hours
What is the absolute magnitude of type 1a supernovas?
-19.3+-0.03
What is scharzchild radius?
The radius of the event horizon of a black hole when you and light will not be able to escape the black hole
R = 2GM/c^2 (escape velocity with light)
What is the range of absolute magnitude on the HR diagram
-10 to 15
What is Hipparcos’ scale?
Classifies astronomical objects by their apparent brightness
What is parallax
The apparent change of the position of a nearer star in comparison to distant stars
Define stefans law
Power output of a black body radiator is proportion to surface area and absolute temperature^4
Formula for intensity
P/(4pi d^2)
What are spectral classes based on?
The strength of absorption lines
What spectral classes are hydrogen balmer lines found in
O B A
What causes hydrogen balmer lines
When stars are hot enough to excite hydrogen to n=2, if too hot it would excite to higher levels
Which class has the strongest balmer lines?
A
The direction of absolute magnitude on HR diagram
-10 to 15 top to bottom
How does red giant become a white dwarf
Uses up all the helium in its core
it will eject its outer layers
Become hotter and dimmer
What is in equilibrium in a main sequence star?
The outward press and inward gravity
When does a star become a red giant?
When hydrogen runs out, helium is then fused to form outer layer which expands and cools
How big are white dwarfs
1.4 solar mass
How do you differentiate red giants and red super giants
red giants < 3 time solar mass
super red giant > 3 times solar mass
What is a binary system
When two stars orbit a common mass
What is a type 1 supernovae
When a star accumulates matter from its companion star in a binary system and explodes after reaching critical mass
What is a type 2 supernovae
It is the death of a high mass star after it runs out of fuel
What have scientist concluded is at the centre of our galaxies and why
Super massive black holes
As gas and stars near the centre appear to orbit quickly
Therefore there must be something with a strong gravitational field
What is dark energy
The reason behind why the universe is accelerating
What is the doppler effect
The compression or spreading out of waves that are emitted or reflected by a moving source
What does the doppler effect do to lines of spectra
Shift them to blue end or red end (red/blue shift)
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What is blue shift and red shift in terms of spectra
Blue shift - when lines of spectra move towards earth
red shift - when lines of spectra move away from earth
What is red shift used in evidence for?
An expanding universe
What is the criteria of using red shift formula
When recessional velocity is much smaller than the speed of light
What are the characteristics of quasars
Extremely large optical red-shifts
Very powerful light output
Not much bigger than a star
How can you estimate the power output of a quasar?
Inverse square law for intensity
What are exoplanets
Planets not within our solar system
What are the two ways of detecting exoplanets
Radial velocity method
Transit method
Explain the radial velocity method
In binary systems stars orbit a common centre of mass which causes them to wobble slightly
This causes a doppler shift in the light received from the star
This causes the line spectrum that are detected to be blue or red shifted
Explain the transit method
Involves observing the intensity of light output, if the star intensity dips regularly this shows there is a another planet in orbit
State the property of quasars that led to its discovery
High power
Suggest why quasars stopped emitting radiation?
quasars are formed around black holes
black hole no longer has matter falling into it
