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Astronomy GCSE Edexcel > Topic Four: Galaxies and Cosmology > Flashcards

Topic Four: Galaxies and Cosmology Flashcards

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1
Q

What is a galaxy?

A

Huge gravitationally bound collections of stars with very little else between them

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2
Q

What are the two small satellite galaxies that orbit the milky way?

A

The small and large magellanic clouds

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3
Q

Explain the appearance of our galaxy from Earth and why it appears this way:

A

Large milky band stretching across the sky

We are looking into the plain of our galaxy from one of its spiral arms

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4
Q

Describe the shape of the Milky Way:

A

A giant disk shaped Catherine Wheel rotating around a central budge

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5
Q

Where in the sky of the Northern Hemisphere can you find the milky way?

A

In a line from Cassiopeia to Cygnus

The galactic centre lies in sagittarius

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6
Q

Describe the three main structural components of our Galaxy:

A

A bulge surrounding the nucleus (black hole)
The disk
The halo

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7
Q

Describe the disk of the Milky Way:

A

Young stars, gas and dust
Four major spiral arms
Is 1-2kpc thick
30kpc in diameter

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8
Q

Describe the halo of the Milky Way:

A 
Globular clusters (dense groups of relatively old stars)
- spherically distributed along the galactic centre
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9
Q

Whereabouts is our solar system found in the Milky Way?

A

One of the spiral arms

10kpc from the nucleus

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10
Q

Apart from stars, what do the spiral arms of the Galaxy contain?

A

Huge clouds of gas and dust that can block light

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11
Q

How can we see the structure of the spiral arms if light is being blocked?

A

Microwave EMR can be seen by radio telescopes on Earth, this wavelength is given off by hydrogen

Doppler shifts in the wavelengths help us work out the galaxy is rotating

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12
Q

Who classified the different types of galaxy?

A

Edwin Hubble in the 1920’s

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13
Q

Describe the Spiral Galaxy:

A

Flattened disk-shaped

e.g. Andromeda

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14
Q

Describe the Barred Spiral Galaxy:

A

Like spiral, has bright bar running through nucleus through which spiral arms appear

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15
Q

Describe the Elliptical Galaxy:

A

Smooth Spheroid of
Stars
Brightest at centre
Dimmest at edge

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16
Q

Describe the Irregular galaxy:

A

Has little structure or symmetry

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17
Q

Describe the Lenticular Galaxy:

A

Class between Elliptical and Spiral

18
Q

What is the local group?

A

Galaxies are grouped together just like stars

Our galaxy is grouped together with 50 others

19
Q

Name 6 galaxies in our Local Group:

A 
Andromeda
Large Magellanic
Small Magellanic 
The Triangulum Galaxy
Pisces Dwarf
Aquarius Dwarf
20
Q

What is a cluster?

A

Many local groups of galaxies can be found in gravitational agglomerations called Clusters
Often there is a giant elliptical galaxy at the centre of a cluster

21
Q

What is a super cluster?

A

A group of clusters held together by gravity

22
Q

What is an Active Galactic Nucleus?

A

Region in the centre of some galaxies emitting huge amounts of radiation - not just visible light

Supermassive black holes at their centre, matter spiralling to black hole emits radiation

23
Q

Name 4 types of active galaxy:

A

Radio galaxies
Seyfert galaxies
Quasars
Blazars

24
Q

Describe Seyfert Galaxies:

A

IR and X-Ray emitted

25
Q

Describe Quasars:

A 
Compact
Extremely Bright
-One of the brightest objects in the universe 
Supermassive black hole at centre 
One of the oldest objects in universe 
- high redshifts
26
Q

Describe Blazars:

A

Emit strongly in all regions of the spectrum

Optical brightness can vary over 1 or 2 days

27
Q

What are absorption lines?

A

Black lines created when light from stare is absorbed by element in the outer layers

28
Q

What is Redshift?

A

Absorption lines are shifted towards the red end of the spectrum when we look at the most distant galaxies
Their wavelength is longer than it should be

29
Q

What can we deduce from Redshift?

A

That distant galaxies are moving away from us and that the universe is expanding
The universe began as an extremely small initial point in the big bang

30
Q

Give an example of Blueshift and explain what this means:

A

Andromeda is moving towards us

31
Q

What is Hubble’s law

A

Hubble saw that fainter galaxies showed greater redshift
The recession velocity is proportional to the distance from us

v = Hd

32
Q

What are the units for Hubble’s constant?

A

Km/s/mpc

If we convert the km into mpc then we can express the units of the Hubble Constant as /s

33
Q

What is the significance of this?

A

1/h gives the age of the universe in seconds

34
Q

How old is the universe?

A

14 billion years

35
Q

What is Cosmic microwave background radiation?

A

Microwave radiation that can be detected coming from the sky in every direction
Perfectly matches the radiation emitted by a black body with a temperature of 2.7 K

36
Q

What is dark matter?

A

Matter which does not emit or reflect radiation but has detectable gravitational effects
Makes up 95% of our universe

37
Q

What could Dark Matter be made of?

A

We don’t know, perhaps it’s made out of Black Holes, Neutrinos, Weakly Interacting Massive Particles.
Or maybe, just maybe, it’s all one massive conspiracy made by the government….
ok ignore that last one I’m getting bored again

38
Q

Who first proposed the existence of dark matter and when?

A

Fritz Zwicky in 1933

39
Q

Give evidence for the existence of Dark Matter:

A

Gravitational lensing - light bent and distorted through huge amount of matter

Rotational curve for a spiral galaxy:

  • stars far away from nucleus travelling much faster than expected
  • only explicable if a great deal of invisible mass was present
40
Q

What is dark energy?

A

Mysterious repulsive force causing accelerating expansion of universe

41
Q

What is the significance of Dark Energy?

A

Expansion of universe not slowing down as previously thought

Astronomy GCSE Edexcel (6 decks)

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