5.5 AstroPhysics Flashcards

Question

Overall fusion reaction

Answer 1

4 proton goes to - helium-4 (2 proton + 2 neutron) - 2 positrons - 2 neutrinos - gamma rays

Answer 2

Stellar Nebula -> Main Sequence Hydrogen runs out and fusion halts, stopping the outwards pressure and causing the core to collapse and the outer layers to expand and cool as the star becomes a red giant. Core collapses further until helium fuses into carbon and oxygen preventing the core from collapsing further. Once all the helium is fused the core collapses further and ejects its outer layers which form a planetary nebula. The remaining core is a white dwarf which is stable as gravitational forces are counteracted by the electron degeneracy pressure

Answer 3

Stellar Nebula -> Main Sequence Hydrogen runs out and fusion halts, stopping the outwards pressure and causing the core to collapse and the outer layers to expand as the star becomes a red super giant. As the core collapses, heavier elements are created by fusion. At each stable fusion stage, the further collapse of the core is prevented by the electron degeneracy pressure and the radiation pressure. Once an iron core has built up the fusion will stop and the core will undergo further gravitational collapse. The immense gravitational forces force protons and electrons to combine to form neutrons, which releases an incredible amount of energy causing a supernova as the outer shell is blown off. During a supernova heavier elements the iron can be formed when the nuclei fuse with neutrons.

Answer 4

Depending on the mass remaining in the core a neutron star may be formed. These are very small and have very high density and are composed mostly of neutrons. The magnetic field of the neutron star can cause the star to emit vast amounts of high energy radiation from its poles. This is called a pulsar. If the neutron star is massive enough the pressure can become so large that the neutron star would collapse to a point and become a black hole

Answer 5

A spectrum that contains all wavelengths over a wide range

Answer 6

Discrete energies that electrons can have when occupying specific orbits.

Answer 7

The spectrum of frequencies emitted due to electron transitions from a higher energy level to a lower one

Answer 8

The pattern of dark lines that would appear on a continuous spectrum when the spectrum is shone through a medium that would absorb some frequencies of light

Answer 9

0 at infinity] -13.6eV at the lowest energy level varying between these but the energy level is always negative

Answer 10

The lowest energy level

Answer 11

They come from hot gasses when an excited electron moves to a lower energy level and emits a photon.

Answer 12

delta E = hf | where delta E is the change in energy resulting from an electron changing energy level

Answer 13

The same wavelengths are absorbed as are emitted

Answer 14

Always just one

Answer 15

By looking at the spectrum of light from the star. It is assumed that the star emits a continuous spectrum and thus any dark lines in the spectrum will be from that wavelength being absorbed by the elements in the stars atmosphere. Therefore by matching the dark lines to known samples of all the elements we can determine the makeup of the stars atmosphere

Answer 16

The gasses in the atmosphere are not hot enough to produce emission spectra

Answer 17

Using a transmission diffraction grating to diffract the light and then using nλ = dsinθ

Answer 18

nλ = dsinθ sinθ <= 1 nλ = d n = d / λ

Answer 19

λmax ∝ 1/T | where λmax is the most common wavelength emitted by a star and T is the peak surface temperature

Answer 20

Peak at λmax. Much higher area under the stars of higher temperature

Answer 21

The total energy emitted per second

Answer 22

``` L=4σπr^2T^4 where L is luminosity σ is stefans constant T is temperature r i s radius ```

Answer 23

Because its radius and thus its surface area increases. And luminosity is proportional to surface area

Answer 24

2.89*10^-3

Answer 25

``` I = L/A where I is intensity L is luminosity A is area the area in this case would be the area of a sphere with a radius equal to the distance from the star to earth since the energy has spread out over that distance ```

Answer 26

Astronomical Unit | The mean distance between the Earth and the Sun

Answer 27

The distance travelled by light in a vacuum in one year

Answer 28

A unit of distance that gives a parallax angle of 1 second of arc using the astronomical unit as the base of the right angled triangle

Answer 29

The shifting in position of a star viewed against a background of distant stars when viewed from different positions, for instance when viewed from Earth at different points of Earths orbit

Answer 30

1/3600 of a degree

Answer 31

Measure the difference in angle between the two extremes of earths orbit. The parallax angle will be half of this. Construct a right angled triangle and do some trig ey

Answer 32

p=1/d where p is the angle in arc seconds and d is the distance in parsecs This works because tan(x) = x at very small x and because parsecs are defined in terms of AU and arc seconds (this only works when a distance of 1AU has been used)

Answer 33

The change in wavelength caused by the relative motion between the wave source and the observer

Answer 34

The apparent increased in wavelength of electromagnetic radiation observed when the source is moving away from the observer

Answer 35

The recessional speed of a galaxy is directly proportional to its distance from us

Answer 36

Relative change in frequency = Relative change in wavelength = v/c

Answer 37

By looking at the absorption spectrum of the star and seeing how much it has shifted

Answer 38

Microwave radiation received from all over the sky originating from after the Big Bang. As the universe has expanded the wavelength of the radiation has increased to just a faint microwave radiation with a peak wavelength corresponding to 2.7K

Answer 39

The universe was created from a single point where all the mass and energy was situated. Since then the universe has expanded from a small dense point to a large and comparatively cool universe. Time and space were both created at the instance of the Big Bang

Answer 40

On a large scale the universe is isotropic and homogeneous and the laws of physics are universal

Answer 41

The same in all directions

Answer 42

Of uniform density when considering a large enough volume

Answer 43

The microwave background at a temperature of 2.7K

Answer 44

The red shift and that galaxies further away are more redshifted than those that are closer

Answer 45

Universe is created and is incredibly small and dense and it begins to rapidly expand. Matter and Antimatter are formed in the form of quarks, leptons and photons. There is slightly more matter than antimatter and as they annihilate they leave a universe dominated by particles not antiparticles. Soon the universe cools enough so that quarks can come together and form protons and neutrons. Many high energy photons are released from matter-antimatter annihilation The temperature cools enough that helium and lithium nuclei can form and then electrons gradually become attached to the present protons. This is called decoupling as the universe becomes transparent and photons can move freely. This is where the photons that are now the CMB originate. Over billions of years the small irregularities that existed at the beginning of the universe become stars, planets and galaxies.

Answer 46

space-time (a 4 dimensional property that combines the three dimensions of space and the fourth dimension of time)

Answer 47

Matter which cannot be seen and does not emit or absorb electromagnetic radiation. It is detected by its gravitational effects

Answer 48

An energy that opposes the attractive force of gravity and exerts negative pressure, causing the expansion of the universe to accelerate

Answer 49

The centripetal acceleration of spinning galaxies is much higher than would be expected from the mass that we can see. There must be more mass that we cannot see that is causing this

Answer 50

Dark Energy - 68% Dark Matter - 27% Ordinary Matter - 5%

Answer 51

Galaxies may be subject to local gravitational effects