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Physics > Astrophysics And Cosmology > Flashcards

Astrophysics And Cosmology Flashcards

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1
Q

What is a planet

A

An object that orbits around a star:

  • With a mass large enough for its own gravity to give a round shape
  • Has cleared its orbit of most other objects
  • Does not undergo fusion reactions
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2
Q

What is a planetary satellite

A

A body in orbit around a planet e.g. Moons or satellites

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3
Q

What is a comet

A

Irregular bodies made of ice, dust and rock with highly elliptical orbits around the sun

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4
Q

Galaxy

A

A collection of starts and interstellar dust and gas. On average there are 10 billion starts in each galaxy.

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5
Q

What is the universe

A

Everything

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6
Q

What is gas pressure

A

The outwards pressure from a nuclei in the core of a star

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7
Q

What is radiation pressure

A

An outwards pressure caused from photons emitted in fusion

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8
Q

How is a protostar formed

A

As dust and gas in a nebula gets closer together gravitational collapse accelerates forming denser regions. These denser regions pull more gas and dust gaining mass and density. Gravitational potential energy is converted into kinetic energy then into temperature. This forms a protostar

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9
Q

How does a protostar become a main sequence star

A

Gravity pulls the gas in the protostar so tightly to the centre that pressure and temperature increases enough for fusion to occur.

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10
Q

How does a star remain in stable equilibrium

A

Gravitational force acts to compress the star but radiation pressure and gas pressure in the core pushes outwards

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11
Q

How does a low mass star become a red giant

A
  • When a low mass star between 0.5-10M begins to lose fuel in the core, the gravitational force is greater than the radiation and gas pressure.
  • The core begins to collapse increasing pressure for hydrogen to fuse into helium in the shell around the core.
  • The star begins to expand.
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12
Q

How does a red giant form a white dwarf

A

Eventually most of the layers of the red giant drift off and forms a planetary nebula and the core remains as a white dwarf.

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13
Q

Characteristics a white dwarf

A
  • High temperature
  • Low luminosity
  • High density
  • Experience electron degeneracy pressure
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14
Q

What is electron degeneracy pressure

A

An outward force provided by electrons in a white dwarf which is caused by the Pauli exclusion principle

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15
Q

What is the Chandrasekhar limit

A

The maximum mass of a core of a star where electron degeneracy pressure will prevent gravitational collapse of the core. 1.44M

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16
Q

How does a high mass star become a red super giant

A
  • In stars with a mass greater than 10 solar masses, when the hydrogen in the core runs low the core begins to collapse.
  • The core of the star is hot enough for the fusion of helium, this causes the core of the star to expand, forming a red super giant.
  • Core of the star is made up of a series of shells that fuse elements up to iron.
17
Q

Why does a supernova happen and what is left behind after

A
  • Iron nuclei cannot fuse as such a reaction cannot produce any energy. This cause the star to become unstable and the layers of the star implode.
  • A black hole or neutron star will be produced
18
Q

Characteristics of a black hole

A
  • Created if the core has a mass greater than 3 solar masses
  • Strong gravitational field
  • High density
19
Q

Characteristics of a neutron star

A
  • Created is a the mass of the star is greater than the Chandrasekhar limit
  • Made up of almost entirely of neutrons
  • Small, can be 10km in diameter
  • Similar density of an atomic nuclei
20
Q

Hertzsprung-Russel diagram

A

A graph showing the relationship between luminosity and temperature in stars (increasing right to left)

21
Q

Why are energy level negative

A

As external energy is required to remove an electron from an atom

22
Q

What happens when electrons make a transition from a higher to lower energy level

A

A photon is emitted and electron loses energy

23
Q

How is an emission spectra line produced

A

Electrons make a transition for a lower energy level emitting a photon with a specific wavelength

24
Q

What is a continuous line spectrum

A

All visible frequencies are present

25
Q

What is an emission line spectra

A

A set of specific frequencies of electromagnetic radiation emitted by excited atoms as their electrons jump to higher energy levels.

26
Q

What is the absorption line spectra

A

A series of dark spectra lines against a continuous a background of a continuous spectrum, as photons pass through a cool gas they are absorbed.

27
Q

Define a parsec (pc)

A

The distance at which a radius of 1 au subtends an angle of 1 arc second

28
Q

Stellar parallax

A

A technique used to determine the distance to stars that are relatively close to earth.

29
Q

What is the cosmological principle

A

The universe is isotropic, homogenous and the law of physics are universal

30
Q

What is isotropic

A

Space is the same in all directions

31
Q

What is homogenous

A

There’s a uniform distribution of matter

32
Q

Red shift

A

When the wavelength of a receding galaxy is stretched moving to the red end of the spectrum

33
Q

Hubble’s law

A

Recessional velocity of a galaxy is direct proportional to its distance from earth

34
Q

What is the Big Bang theory

A

At some moment in the past all matter in the universe existed in a singularity, which the expanded giving birth to space and time.

35
Q

Evidence for the Big Bang

A
  • Red shift
  • Microwave background radiation 2.7k
  • The universe gave out gamma radiation but as the universe expanded the wavelength was stretched giving microwave radiation.
36
Q

Main stages in the evolution of the universe

A
  • At 0s the universe was a singularity
  • As the universe expanded it cooled
  • High energy gamma photons released which stretched as the universe cools
  • At 10⁻⁶s quarks and leptons formed
  • At 10⁻³s first hadrons formed
  • More matter than antimatter
  • At 100s protons and neutrons fused together to form deuterium and helium
  • At 380000 years the universe cool,ed enough for the first atom to form
  • At 300 millions years stars formed through gravitational forces
  • Temperature of 2.7k
37
Q

What is the universe made up of

A
  • Dark matter
  • Dark energy (Causing the universe to expand at an increasing rate)
  • Small percentage of ordinary matter
38
Q

What is Wien’s displacement law

A

λmax ∝ 1/T

T= surface temperature

39
Q

What is Stefan law

A

L=4πr²σT⁴

Physics (14 decks)

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