Option E - Astrophysics Flashcards

Question

Why does a hot body emit light?

Answer 1

Due to electron energy transitions

Answer 2

Calculating the total intensity of light emitted from a star Power per unit area = σT⁴ σ = Stefan-Boltzmann constant

Answer 3

Total power emitted = L (luminosity) L = σAT⁴

Answer 4

As the temperature incrases, the wavelength of the peak gets less:

Answer 5

1. Its temperature 2. Its chemical composition 3. Its colour

Answer 6

O - blue B - blue-white A - white F - yellow-white G - yellow K - orange M - red (**O**h **B**e **A** **F**ine **G**irl **K**iss **M**e)

Answer 7

Yes | (red-shift and blue-shift)

Answer 8

Star moving away: longer λ - red shift Star moving closer: shorter λ - blue shift

Answer 9

1. Red giants 2. Red supergiants 3. Cepheids 4. White dwarfs

Answer 10

- A cool star - Gives out a lot of energy - Very big

Answer 11

- A cool star - Very big, bigger than giants - Very rare

Answer 12

- A small star - Very hot - Hotter than the sun but only the size of the Earth - Low luminosity

Answer 13

- Stars with changing luminosity - Size changes too, as it gets bigger its luminosity increases

Answer 14

- From the analysis of the brightness of the light from the star - Over time the brightness shows a periodic variation - Variation is a result of its orbit, one star gets in front of the other

Answer 15

- From the analysis of the spectrum of light from the star - The wavelengths show periodic shift (red and blue) - Due to Doppler effect - As a result of its orbit, the stars move periodically towards and away from the Earth

Answer 16

A star that orbits around each other (or their common centre of mass

Answer 17

A star that is not gravitationally bound to other stars

Answer 18

- Cepheid stars are hard to position because they have variable size and luminosity - The scale is not linear - The mass of main sequence stars is dependent on their position on the HR diagram

Answer 19

d = distance between the binary stars (M₁ + M₂) = total mass of the two stars

Answer 20

Parallel angle of one second:

Answer 21

The apparent movement of a star from Earth's point of view due to the earth's movement in its orbit.

Answer 22

- The relative position changes during one year - Can be found by measuring the angle between rays from the object to two fixed points - The telescope is lined up with the star on one day and then again half a year later when the Earth is on the other side of the Sun - The angle is calculated with the help of a distance to a very distant star (this way the distance won't be affected by the movement of the Earth)

Answer 23

Because the star needs to be close enough to show apparent motion with respect to the Earth. If the star does not "move" in the sky during the Earth's orbit, the angle cannot be measured

Answer 24

One degree can be split into 60 arc minutes (') Each arc minute can be split into 60 arc seconds ('')

Answer 25

A scale used to compare the brightnesses of stars as viewed from Earth

Answer 26

- Inverse scale - The bigger the number the smaller the brightness - A magnitude 1 star is 100 brighter than a 6 - Logarithmic scale - Magnitude depends on luminosity

Answer 27

The magnitude of a star viewed from a distance of 10 pc

Answer 28

The apparent magnitude of a star is a measure of its brightness as viewed from the Earth. The absolute magnitude is a measure of luminosity

Answer 29

Its spectrum

Answer 30

By using the inverse square law to calculate the distance from Earth

Answer 31

It is limited to measuring stellar distances less than about 10 Mpc

Answer 32

A method of using the spectrum of a star to estimate is luminosity. (also the distance after the apparent brightness is calculated)

Answer 33

An unstable star in which the outer layers undergo a periodic expansion and contraction, which produces a periodic variation in its luminosity

Answer 34

Measuring distances to stars further than 10 Mpc with the help of stellar parallax

Answer 35

They are directly proportional

Answer 36

If a Cepheid variable is located in a particular galaxy, the distance to the galaxy may be determined with the help of a Cepheid variable

Answer 37

- Infinitely big, infinitely old, static, and uniform - Gravitational force on each star was the same in each direction

Answer 38

- If Newton's model of the universe were to be true, and the sky had an infinite number of stars, the sky would never be dark - Even if some stars were blocked, the energy absorbed would be re-emitted and would eventually reach the Earth - The most probable solution is that the universe is not infinite and there is not an infinite number of stars - Time is not infinite, the light from some of the stars has not reached the Earth yet

Answer 39

The red-shift of light from distant galaxies (= the galaxies are moving away)

Answer 40

The space is growing, rather than it is speading into the nothingness that surrounds it. The galaxies therefore move apart from each other because the space between them is expanding

Answer 41

Space **and** time

Answer 42

If the universe is currently expanding and all its particles are moving away from each other, at some point in the past all the galaxies would have been at the same point approximately 15 billion years ago.

Answer 43

- In the beginning the universe was packed tightly with photons and other fundamental particles - The photons are still present but have a much longer wavelength (microwaves) - They were thought to be uniform at first - Very small variations within the microwaves were detected - This shows that the universe was not completely uniform in the beginning, enabling galaxies to form

Answer 44

- The universe is cooling down

Answer 45

One that keeps expanding

Answer 46

One of which rate of expansion tends to zero at infinite time

Answer 47

One that stops expanding and starts to contract eventually

Answer 48

The density at which the closed universe becomes open.

Answer 49

- The rate of expansion is slowing down due to gravity - Whether it is slowing down enough to stop depends on the density of it - If the density is bigger than the critical density, it will stop expanding and start to contract, eventually ending in a bigh crunch - If the density is lower than the critical density, it will continue to expand forever

Answer 50

- Normally the density can be measured by measuring the mass of all the stars in a given volume - The total mass calculated is not enough to give the gravitational attraction to hold it together - The total mass of all the stars is only about 4% of the whole mass - The rest of this mass is dark matter - There's a lot of stuff we don't know

Answer 51

- Any matter that does not interact with light - May consist of neutrinos - May consist of new particles (WIMPs or MACHOs)

Answer 52

Shorthand for massive astronomical compact halo objects - There is some evidence that lots of matter does exist in these groupings - Can be thought of as low-mass 'failed' stars or high-mass planets, or black holes - Produce little or no light - Possibly a part of dark matter

Answer 53

Shorthand for weakly interacting massive particles - New particles that we don't know about - Possibly a part of dark matter

Answer 54

That it is open

Answer 55

H₀ = Hubble's constant

Answer 56

Because they are extremely expensive and require the funding of several countries e.g. Gamma-ray Large Area Space Telescope (GLAST), which involves the US, France, Germany, Japan, Italy, and Sweden

Answer 57

In terms of the advancement of science, yes. In terms of money, no one knows.

Answer 58

- Huge clouds of gas and dust need to be compressed - Usually caused by an exploding supernova or a collision between two dust clouds - As the gas atoms are pulled together, they gain kinetic energy and the temperature increases - The increase in temperature causes an outward pressure that pushes against the gravitational force - As the atoms get closer, the gravitational force increases, so the gas continues to collapse and get hot infinitely

Answer 59

1. As the cloud collapses, a dense coreis formed surrounded by a cloud of gas and dust 2. The centre of the core rapidly contracts, resulting in high temperature and pressure 3. After a while, the radiation from the star blows away the dust cloud and the mass of the star stabilises 4. The core continues to contract and heat up until the atoms are moving fast enough for fusion to take place 5. Once fusion starts, the increase in temperature causes greater pressure, balancing the inward force of gravity. 6. The star stops contracting and becomes a main sequence star

Answer 60

1. When all the hydrogen in the core has become helium, the core is no longer producing energy and is no longer in equilibrium 2. The thermal pressure drops, causing the core to rapidly compress 3. The compression results in an increased temperature, which heats the hydrogen gas outside the core, causing it to start fusing 4. As this happens the outer layers expand and the star becomes a giant 5. The helium in the core starts to fuse to carbon 6. If the star has sufficient mass, the red giant can continue to fuse higher and higher elements and nucleosynthesis can continue (layered structure)

Answer 61

The luminosity of massive main sequence stars is greater than stars of small mass; this enables us to know where the different stars join the main sequence line.

Answer 62

Chandrasekhar limit: 1.4 M_O - The mass of a white drawf cannot exceed this - Results from stars with a mass of max 4 M_O - If the mass of the star is greater than this, it will not become a white drawf

Answer 63

Oppenheimer-Volkoff limit: 3 M_O - The maximum mass of a stable neutron star - Neutron stars of bigger masses become black holes

Answer 64

- A red giant forms a planetary nebula and then becomes a white dwarf - A white drawf is stable due to electron degeneracy pressure - A red supergiant experiences a supernova and becomes a neutron star or collapses to a black hole - A neutron star is stable due to neutron degeneracy pressure

Answer 65

- As a star collapses, the speed of rotation increases - A neutron star rotates very fast - The magnetic field increases when a star collapses into a neutron star - The rotating magnetic field causes charged particles to accelerate, which emit EM radiation along the ling of the poles - When the neutron star rotates, its beam of radiation sweeps around like a lighthouse in regular intervals (0.03 s to 1.3 s)

Answer 66

- Not randomly - Tend to be found clustered together (galactic cluster) - Galactic clusters and also group together to form galactic superclusters

Answer 67

Because the universe is expanding

Answer 68

∆λ = change in wavelength (shift λ = original wavelength v = relative velocity c = speed of light

Answer 69

The recession of speed is directly related to the distance to the galaxy:

Answer 70

- The law assumes that the velocity is constant - Gravitational attraction slows the galaxies down; the recessional velocity we measure today is smaller than it was

Answer 71

- In the beginning there were no atoms because the temperature was so high that the photons had enough energy to ionise atoms - Any electron combining with a proton to form a hydrogen atom would be knocked off - When the universe expanded and cooled down, the photons did not have enough energy to ionise atoms - Electrons were able to start combining with protons to form atoms

Answer 72

If the universe had spread out uniformly the graviational attraction between each particle would have been balanced and the particles would not have been brought together to form galaxies. Thus there must have been some irregularities to provide the starting point for all the galaxies