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astro Flashcards

(66 cards)

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1
Q

Define Luminosity

A

rate of light energy released/power output of a star

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2
Q

Define intensity

A

power received from a star per unit area

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3
Q

What is the apparent magnitude of a star?

A

How bright an object appears in the sky (depends on luminosity and distance from Earth

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4
Q

What does the Hipparcos scale measure and how does it work?

A

Apparent magnitudes,
bright stars have apparent magnitude of 1 and faint have apparent magnitude of 6. A 1 magnitude star appears 100 time brighter than a 6 magnitude star

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5
Q

What ratio does the intensity of a star change in the Hipparcos scale?

A

2.51 (it is logarithmic)

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6
Q

What is the absolute magnitude of a star?

A

What its apparent magnitude would be if it were 10 parsecs away from Earth

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7
Q

What is meant by parallax

A

Apparent change of position of a nearer star with the same background as a result of #earths orbit around sun (in January star appears in one position, but 6 months later we on other side of sun and so star appears to have moved)

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8
Q

How is parallax measured?

A

As a right angled triangle (distance between sun and Earth, distance between sun and star, and then parallax angle can be calculated)

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9
Q

Define one astronomical unit

A

Average distance between centre of Earth and centre of sun

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10
Q

Define one parsec

A

Distance at which 1 AU subtends at an angle of 1 arcsecond

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11
Q

Define a lightyear

A

Distance EM wave travels in one year in a vacuum

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12
Q

What is black body radiator

A

A perfect emitter and absorber of all possible wavelengths of radiation

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13
Q

What does Wiens displacement law tell us if T increases?

A

frequency increases so energy of wave increases

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14
Q

What law does light intensity follow and what should be noted about how light is emitted?

A

Inverse square law
emitted equally in all directions

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15
Q

How can intensity of light be calculated using power output and distance?

A

I = 4pid^2

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16
Q

What is the approximate temperature of our sun?

A

6000K

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17
Q

How can stars be classified into spectral classes?

A

Based off of the strength of their absorption lines which are dependent on temperature (energy of star is dependent on temp- Wiens Law)

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18
Q

Which spectra are Hydrogen Balmer Lines found in? How are they caused?

A

O, B and A
Excitation of hydrogen atoms from n=2 state. If temp is higher, these lines will not be found as energy will raise energy levels to above n=2 or ionise them. If temp too low, hydrogen atoms are unlikely to become excited at all.

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19
Q

Order of spectral classes

A

O
B
A
F
G
K
M

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20
Q

Temp, colour and prominent absorption lines in each spectral class

A

O = blue, 25000-50000, He+, He and H
B = blue 11000-25000, He, H
A = white/blue 7500-1100, H, ionised metals
F = white, 6000-7500, Ionised metals
G = yellow/white, 5000-6000, Ionised and neutral metals
K = orange, 3500-6000, neutral metals
M = red <3500, neutral metals, titanium oxide

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21
Q

Sketch the Hertzsprung Russel Diagram and mark where the sun is, main sequence, giants, supergiants and dwarfs are. Label axes too.

A

sun at 6000K and 5 absolute
top = supergiants
just below and to right is giants
Bottom left = dwarfs
Main sequence = curve
Absolute against spectral class/temp

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22
Q

Compare a red giant to main sequence

A

Brighter and cooler

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23
Q

Compare a white dwarf to a main sequence star

A

Dimmer and hotter

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24
Q

Draw roughly the life cycle of a star

A

proto (left)
To main sequence
to red giant (top right)
curving around the top towhite dwarf (bottom left)

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25
What is a protostar?
A cloud of gas and dust containing fragments of varying masses that clump together under gravity
26
How is a protostar formed?
Clumps of varying masses clamp together under gravity. These irregular clumps rotate and gravity forces them inwards, increasing the density
27
What surrounds a protostar? How does this disappear?
a disc of material - circumstellar disc). As protostar gets denser it gets hotter and so elements start to fuse, this produces a stellar win that blows surrounding material away
28
How is a main sequence star formed?
The outward force due to becomes equal to inward force of gravity and so the star is stable
29
What happens in a main sequence star?
Hydrogen nuclei are fused into helium. The greater the mass, the shorter the main sequence as fuel used quicker
30
Which masses convert into what following main sequence?
<3 solar masses = red giant > 3 solar masses = red supergiant
31
When will a white dwarf be formed? Describe it too
Red giant with mass <1.4 solar masses runs out of fuel and core contracts due to strength of gravity. A planetary nebula forms around as outer layers are thrown off
32
When will a supernove be formed?
Red giant between 1.4 and 3 solar masses Supergiant > 3 solar masses
33
What happens in a red giant?
Temperature of core increases and begins to fuse helium nuclei. Outer layers start to expand and cool
34
What happens in a red supergiant?
Temperature of core increases and begins to fuse helium nuclei (on a larger scale than red giant)
35
What is a supernova?
When all fuel runs out, fusion stops and the core collapses inwards suddenly and becomes rigid. The outer layers collapse in and then rebound launching them into space like a shockwave. As this wave passes through material, elements heavier than iron are fused and flung into space
36
Key characteristic of supernovae
Rapidly increasing absolute magnitude. Same critical mass (similar peak absolute magnitude Consistent light curves
37
Key characteristic of supernovae
Rapidly increasing absolute magnitude. Same critical mass (similar peak absolute magnitude Consistent light curves
38
Use of supernovae
Standard candles (known absolute magnitude)
39
What is a neutron star?
Core of large star collapses, and so gravity is so strong protons and electrons are being fused together to form neutrons. Incredible dense. Pulsars are spinning neutron stars
40
What is the event horizon?
Point at which escape velocity is greater than the speed of light
41
What is a black hole?
Core of giant star collapses but gravity is so strong neutrons cannot cope. The pull is so strong not even light can escape
42
What is the Schwarzchild radius?
Radius of event horizon
43
What is a binary system?
Two stars orbit a common mass
44
What is a type 1 supernova?
A star accumulates matter from its companion star in a binary system and explodes after reaching a critical mass
45
What is a type 1a supernova?
A type 1 supernova with a white dwarf, the companion star runs out fuel and expands. This allows white dwarf to accumulate some of its mass. When the white dwarf reached its critical mass, it explodes into a supernova.
46
Why do scientists believe there are super massive black holes?
Stars near the centre of galaxies appear to be orbiting very quickly
47
How can a supermassive black hole form?
Collapse of massive gas clouds while galaxy was forming Normal black hole that accumulated huge amounts of matter over millions of years Several normal black holes merging together
48
How does Hubble's Law show that the universe is expanding?
Type 1a supernova appear dimmer than expected meaning they are more distant than Hubble predicted
49
What is thought to be the reason behind the universe accelerating?
Dark energy
50
What is dark energy?
overall repulsive effect throughout the whole universe. Constant throughout universe and therefore has greater effect than gravity to expansion of universe increases
51
What is the doppler effect?
Compression or spreading out of waves by a moving source
52
What is the difference between blue shift and red shift?
Line spectra shifted towards blue end of spectrum are moving towards Earth, red are moving away
53
When can red shift not formula be used?
When v is similar to c
54
What can be used to identify binary star systems?
Doppler effect or telescope Spectroscopic binaries are ones which are too close to be resolved by a telescope and so doppler shift can be used to identify them
55
How does doppler effect provide evidence of binary star?
As one of the stars is moving away line spectra towards red end of spectrum whilst the other star is moving towards and so line spectra towards blue end of spectra
56
When stars in a binary system overlap what can be said?
They eclipse each other No doppler effect
57
What is a quasar?
Very distant objects with very large red shifts. Very powerful light output Inverse square law suggests power output it is equivalent to that of several galaxies Not much bigger than star
58
How can Hubble's law suggest age of universe?
v = H/d t = d/v so t = 1/H Ensure H is in converted to SI units
59
What does the Big Bang theory suggest?
Universe began from a singularity that was infinitely small and infinitely hot. There was then a big explosion from this point. Following the bang, radiation would have lost energy and been red-shifted, the remains are known as CMBR (microwave radiation)
60
What is evidence of the Big Bang?
CMBR relative abundance ratio of H:He of 3:1
61
How does nuclear fusion provide evidence for The Big Bang?
In early stages of Big Bang nuclear fusion converted hydrogen nuclei into helium nuclei. The universe then cooled too much and fusion stopped. Only 25% of hydrogen nuclei were fused into helium nuclei. This ratio is still seen today
62
Ways of detecting exo-planets
Radial Velocity Method Transit Method Telescope
63
What is an exoplanet and why can they be hard to detect?
Planets that are not within our solar system. They can be obscured the light of their host stars
64
What does the radial velocity method entail?
Star and planet orbit common centre This creates a doppler shift in light received from star Blue shifted when moving towards Earth, red shifted when moving away. Works best with higher mass planets as they have exert a greater force. Time period of doppler shift = time period of orbit
65
What does the transit method of finding exoplanets entail?
This is achieved through observing the intensity of the light output of the star. When the planet crosses infront of the star, the intensity dips. This level of dip can be used to find size and orbital period of planet. Only works if line of sight to the star is in plane of orbit
66
In 1999 why was their controversy over measurements of supernovae?
They were not the same as Hubbles law suggested Conveyed the universe is expanding No known energy source for this, 'dark energy' created controversy

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