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Physics > Astrophysics > Flashcards

Astrophysics Flashcards

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1
Q

What are 3 ways to categorize a star’s surface temperature?

A

1) lamda max (wien’s law) 2) colour index (taking 2 photographs and applying 2 filters and finding the difference between the magnitudes of the two images)
3) absorption spectrum and spectral class

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2
Q

Definition of a planet.

A

1) Orbits a star
2) Has enough mass to be more or less spherical
3) Has cleared orbit from other bodies

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3
Q

Name the 4 inner and the 4 outer planets. What distinguishes them?

A

Inner: Mercury, Venus, Earth, Mars -> rocky & metal cores
Outer: Jupiter, Saturn, Uranus, Neptune -> frozen gas

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4
Q

What is the Kuiper Belt?

A

a bunch of icy bodies that are beyond Neptune, in the Pluto region

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5
Q

What is the Oort Cloud?

A

A vast cloud that lies even beyond the Kuiper Bell

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6
Q

What are comets? How do their tails come about?

A

Icy bodies (that usually orbit the Sun, so they can be seen to move slowly)

Evaporation of the material on its surface and that material then gets blown away by the solar wind, so the tail always points away from the Sun

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7
Q

What are meteors?

A

particles burning up as they enter the atmosphere

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8
Q

What are asteroids?

A

rocky body

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9
Q

What are exoplanets?

A

Planets of another solar system

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10
Q

What feature of planets, as opposed to stars, made them of particular interest to study to humans over millennia?

A

Stars remain in fixed patterns called constellations, whereas planets wander among the nightsky.

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11
Q

What is a nebula?

A

Vast cloud of dust and gas

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12
Q

Which pressures oppose gravity in stars?

A

Radiation pressure: photons colliding with particles
Gas pressure: kinetic energy of particles

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13
Q

What is Olbers’ paradox?

A

the contradiction that in an infinite, homogenous and static universe populated with stars, the night sky should be glowing bright with star light from all directions.

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14
Q

What is a homogenous universe?

A

it looks the same, no matter if you look at it from here, or from another galaxy far far away

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15
Q

What does isotropic /isotropy mean?

A

No matter in which direction you look, the universe will look the same.

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16
Q

What is luminosity?

A

power radiated by sun in all directions in watts

17
Q

What is (apparent) brightness?

A

The power per m2 received at some point in space, e.g. on Earth

18
Q

Why is the inverse square law a bad explanation for Olber’s paradox?

A

Because the assuming a homogeneous density of stars in the universe, the number of stars in a spherical shell around the observer increases as the square of the distance to the shell, so the decrease in brightness from more distant stars is counterbalanced by the increase in number of stars contributing starlight to the overall brightness.

19
Q

What is the solution to Olber’s paradox?

A

The light from stars that are super far away hasn’t reached us yet, so the universe can’t have existed for forever (at least not with stars) –> non-static system

20
Q

What is the Hubble constant?

A

expansion of universe per time

21
Q

What is the cosmic scale factor?

A

measure of relative expansion/size of the universe

22
Q

What is neutron capture?

A

The neutron gets captured by the nucleus due to the strong nuclear force

23
Q

What is the r-process?

A

r: super hot, before supernova type 2, super fast neutron capture, can be multiple neutrons at the same time, faster than beta-decay and thus results in heavier/neutron-rich isotopes

24
Q

What is the s process?

A

s: happens in stars that are in intermediate temperatures, neutrons go in singedly into the nuclei, i.e. slow/normal neutron capture

25
Q

What are similarities between the s process and r process?

A

For both there will be beta- decays, this is how the neutrons become protons and higher elements than iron are made

26
Q

What is the Λ-CDM cosmological model?

A

a dynamic, cosmological (big bang) model, with dark matter and dark energy & a flat universe

27
Q

What are MACHOS?

A

massive astrophysical objects, like black and brown dwarfs

28
Q

What are WIMPS?

A

weakly interactive massive particles, like neutrinos

29
Q

What is supersymmetry (SUSY)? Why is it proposed?

A

Every particle in the standard model has a supersymmetric partner (superpartner), so particles that are very massive, but hardly interacting

It is proposed because the MACHOS are not enough mass to explain the high velocity of bodies in the outer rim of galaxies, so besides the only proven WIMP (neutrino), there has to be more

30
Q

What is Jean’s criterion?

A

A nebula will collapse to form a star. If the mass of the cloud > Jean’s mass or if the particle’s magnitude of potential energy > their kinetic energy

Physics (3 decks)

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