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Physics > Astrophysics (M5) > Flashcards

Astrophysics (M5) Flashcards

1
Q

Luminosity

A

The total radiant power output of a star
Symbol: L
Unit: W

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2
Q

Hertzsprung-Russel diagram

A

A graph showing the relationship between the luminosity of stars in our galaxy and their average surface temperature, with temperature increasing from right to left.

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3
Q

Planetary nebula

A

The outer layers of a red giant that have drifted off into space, leaving the hot core behind at the centre as a white dwarf.

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4
Q

White dwarf

A

A very dense star formed from the core of a red giant, in which no fusion takes place.

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5
Q

Singularity

A

The region in a black hole where the volume tends towards zero. A place where matter is compressed down to an infinitely tiny point.

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6
Q

Electron degeneracy pressure

A

A quantum-mechanical pressure created by the electrons in the core of a collapsing star due to the Pauli exclusion principle.

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7
Q

Neutron degeneracy pressure

A

Created by collapsing start being so dense that electrons and protons are fired to form neutrons. This balances the gravitational force collapsing the star.

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8
Q

Chandrasekhar limit

A

The mass of a star’s core beneath which the electron degeneracy pressure is sufficient to prevent gravitational collapse.
1.44 solar masses

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9
Q

Supernova

A

The implosion of a red supergrass at the end of its life, which leads to subsequent ejection of stellar matter into space, leaving an inert remnant core.

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10
Q

Black hole

A

After a star has gone supernova, if the core has a mass greater than about 3 solar masses, the gravitational collapse continues to compress the core. The result is a gravitational field so strong that its escape velocity is greater than the speed of light.
Super- massive black holes with several million solar masses are thought to be at the centre of most galaxies.

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11
Q

Neutron star

A

If the mass of the core after a supernova is greater than the Chandrasekhar limit, the gravitational collapse continues, forming a neutron star.
Made almost entirely of neutrons
Can be very small - 10km in diameter
Typical mass of about 2 solar masses
Density similar to an atomic nucleus - 10^17 kgm^-3

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12
Q

Red giant

A

Evolve from main sequence stars with 0.5-10 solar masses.
When fuel runs out in a main sequence, fusion stops so gravity is greater than radiation and gas pressure. Core begins to collapse and pressure increases.
Fusion starts in a shell around the core

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13
Q

Red supergiant

A

A massive star in the last stages of its life before it implodes in a supernova.
Mass 0.5-10 solar masses
Heat of core means helium nuclei move fast enough to overcome electrostatic repulsion and fusion starts.
Heavier elements form in layers around the core.
Inert iron core is unstable.

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14
Q

Planet

A

An object in orbit around a star with 3 main characteristics:
~mass large enough for its own gravity to hive it a round shape
~no fusion reactions
~cleared its orbit of most other objects

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15
Q

Solar system

A

Our solar system contains the Sun and all objects that orbit it. It is one of many.
In 2014 over 1100 other solar systems had been discovered.

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16
Q

Galaxy

A

A collection of stars and interstellar dust and gas. On average a galaxy will contain 100 billion stars, a significant proportion of which have their own solar system.

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17
Q

Planetary satellite

A

A body in orbit around a planet. This includes moons and man-made satellites.

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18
Q

Comet

A

A small, irregular body made up of ice, dust and small pieces of rock.
Few hundred metres to tens of km across.
All orbit the Sun mainly in highly eccentric elliptical orbits.
As they approach the Sun, some develop spectacular tails.

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19
Q

Asteroid

A

An object too small and uneven to be a planet, usually in a near-circular orbits around the Sun and without the ice present in comets.

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20
Q

Fusion

A

A process in which two smaller nuclei join together to form one larger nucleus.

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21
Q

Radiation pressure

A

Pressure from the photons in the core of a star which acts outwards to counteract the pressure from the gravitational force pulling the matter inwards.

22
Q

Gas pressure

A

In stars, the pressure of the nuclei in the star’s core pushing outwards and counteracting the gravitational force pulling the star inwards.

23
Q

Nebulae

A

A cloud of dust and gas (mainly hydrogen) often many hundreds of times bigger than our solar system.

24
Q

Protostar

A

A very hot, very dense sphere of condensing dust and gas that is on the way to becoming a star.

25
Q

Main sequence star

A

The main period on an HR diagram in a star’s life during which it is stable.

26
Q

Evolution of the universe (earlier)

A

0: time and space are created, the universe is a singularity

10^-35: Universe expands rapidly, incredible acceleration. No matter just EM radiation in the form of high energy Gamma rays. Temp=10^28

10^-6: First fundamental particles gain mass through the Higgs boson.

10^-3: Quarks combine to form hadrons.

1: Creation of matter through pair production stops once the temperature has dropped to about 10^9 K.

100: Protons and neutrons fuse together to form small nuclei eg helium. Expansion is so rapid that heaviest element is lithium. 25% of matter is primordial helium.

27
Q

Evolution of the universe (later)

A

380,000: Universe cools enough for atoms to form. EM radiation from this stage is now CMBR

30 million: First stars appear. Nuclear fusion in these stars allows elements beyond lithium to form.

200 million: The Milky Way forms as gravitational forced pull clouds of hydrogen and existing stars together.

9 billion: The solar system forms from nebulae left by a supernova. Planets form 1 billion years after the sun.

11 billion: Primitive life on earth begins 1 billion years after its creation

13.7 billion: Around 200,000 years ago the first modern humans evolve. Temperature is 2.7 K.

28
Q

Dark matter evidence

A

Velocity of stars in galaxies does not decrease further from the centre as predicted.
This can be explained if the mass of the galaxy is not concentrated in the centre but most visible mass is.
There must be another type of mass that we cannot see. 27% of the universe must be dark matter.

29
Q

Dark energy evidence

A

~All type 1A supernovae have the same luminosity so the distance can be measured using its intensity.
~Luminosity also measured from the dappled effect and they are not the same - dimmer than expected therefore further than expected.
~They are accelerating so there must be a resultant force
~This must mean there is energy supplying that force

30
Q

How to use the Doppler equations

A

Lambda and f are the values calculated in a lab.
Equation can only be used for a galaxies moving at far less than the speed of light.

31
Q

Age of the universe

A

Age (in seconds) = 1/H0

32
Q

Parsec

A

The distance at which a radius of 1 AU subtends an angle of one arcsecond (1/3600 degrees)

33
Q

Astronomical unit

A

1AU = 1.5x10^11

34
Q

Intensity of a star

A

I = P/A = L/A = L/4piD^2

35
Q

Wien’s law as a ratio

A

m1/m2 = T2/T1

36
Q

Homogeneous

A

Uniform in terms of the distribution of matter across the universe when viewed on a sufficiently large scale.

37
Q

Isotropic

A

The same in all directions - for example the universe appearing the same to any observer regardless of position.

38
Q

CMBR

A

Cosmic Microwave Background Radiation. Likely caused by and therefore evidence for the big bang. Gamma radiation from big bang stretched with universe expansion so now microwaves.
Temperature of 2.7K

39
Q

Hubble’s law

A

The recessional speed v of a galaxy is almost directly proportional to its distance d from Earth.

40
Q

Hubble equation

A

v = H0d

41
Q

Cosmological principle

A

The assumption that, when viewed on a large enough scale, the universe is homogeneous and isotropic, and the laws of physics are universal.

42
Q

Satellite

A

A body orbiting around a planet

43
Q

Geostationary satellite

A

One that remains in the same position relative to a spot on the Earth’s surface by orbiting in the direction of the Earth’s rotation over the equator with a period of 24 hours.

44
Q

Derivation of speed of a satellite

A

F = mv^2/r = GMm/r^2
v = root(GM/r)

45
Q

Kepler’s first law

A

The orbit of a planet is an ellipse with the Sun at one of the foci.

46
Q

Kepler’s second law

A

A line segment connecting a planet to the Sun sweeps out equal areas during equal intervals of time.

47
Q

Kepler’s third law

A

The square of the orbital period T of a planet is directly proportional to the cube of its average distance r from the sun.

48
Q

Emission line spectra

A

Each element produces a unique emission line spectrum because of its unique set of energy levels.

49
Q

Continuous spectra

A

All visible frequencies of wavelengths are present. The atoms of a heated solid metal (eg a lamp filament) will produce this type of spectrum.

50
Q

Absorption line spectra

A

This type of spectrum has a series of dark spectral lines against the background of a continuous spectrum. The dark lines have exactly the same wavelengths as the bright emission spectral lines for the same gas atoms.

Physics (18 decks)

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