Cosmology Flashcards

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1
Q

What is redshift?

A

Absorption lines of galaxy moving away are shifted to the left (red end)

Bigger velocity → Bigger redshift

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2
Q

What is blueshift?

A

Absorption lines of galaxy moving towards are shifted to the right (blue end)

Bigger velocity → Bigger blueshift

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3
Q

How can we potentially tell if a galaxy is rotating?

A

One side is redshifted

Other side is blueshifted

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4
Q

If a galaxy does not have one side redshifted and one side blueshifted

could it still be rotating?

A

Yes, if the rotation isn’t along the line between the galaxy and Earth

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5
Q

How do you calculate the velocity of a galaxy given its redshift?

A

v = zc

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6
Q

Is a redshift velocity the true velocity of a star?

A

No, the star could have a v|

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7
Q

For this binary star system

  1. When is redshift of star A maximum?
  2. When is redshift = 0?
  3. When is blueshift maximum?
A
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8
Q

What is Hubble’s law?

A

A galaxy’s recessional velocity is proportional to its distance from Earth

v ∝ d

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9
Q

How can you use this graph to calculate the age of the Universe?

A

(Reciprocal of the gradient)

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10
Q

Why does this graph not mean Earth is at the centre of the Universe?

A

This graph would be produced if you took measurements from any galaxy

All galaxies are moving away from every other galaxy

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11
Q

What is the radial velocity method?

A

Small redshift of star caused by exoplanet

Used to identify exoplanets

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12
Q

What is the transit method?

A

Regular dip in brightness of star due to exoplanet passing in front

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13
Q

What is an exoplanet?

A

A planet in another solar system

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14
Q

Why are exoplanets so difficult to detect?

A

Exoplanets don’t emit light, they only reflect

And it is a tiny amount compared to the star

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15
Q

What are the key stages of the Big Bang Theory?

A

1 Photons produce particles of matter & antimatter from a vacuum

2 An excess of matter over antimatter occurs

3 Nuclear fusion occurs

4 Nuclear fusion stops

5 Atoms form

6 Stars & galaxies form

7 Nuclear Fusion occurs in stars

8 Life starts

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16
Q

What is the main evidence in support of the big bang?

Explain what it is

A

Cosmic Microwave Background

Radiation leftover from when the Universe formed neutral atoms

(redshifted to microwaves as Universe has expanded)

17
Q

What is a Quasar?

A

Very luminous galaxy nucleus where mass is spiraling into the supermassive blackhole at the center

18
Q

What is required for a quasar to form?

A

An accretion disk (gas, dust and matter) close to the supermassive black hole at the center

19
Q

Why can’t most quasars be detected?

A

Only detected if Earth is in line with radiation jets

20
Q

Why are radiowaves detected from a Quasar?

A

Emitted radiation is massively redshifted to radiowaves

21
Q

What does the large redshift of Quasars tell us about Quasars?

A

They are some of the most distant objects in the Universe

22
Q

What is the Schwarzschild Radius for an object?

A

What it’s radius would have to be shrunk to for it to become a black hole
(where escape velocity > speed of light)

23
Q

How do Type 1A Supernovae Form?

A
  • In a binary star System
  • One star has become a White Dwarf
  • But has absorbed enough mass from other so M > 1.4xMSun
24
Q

What are Type 1A Supernovae useful for?

A

One of the brightest ‘Standard Candles’ (known Absolute Magnitude)
Used to measure distances to furthest galaxies

25
Q

What is the Absolute Magnitude curve for a Type 1A Supernovae?

A
26
Q

What do the redshifts of the most distant Type 1A Supernovae tell us?

A

The redshifts are greater than expected
So Universe’s expansion is accelerating
Dark energy causes this acceleration

27
Q

In the equation for doppler shift what do the different λ represent?

A

λ0 → Wavelength if observer was stationary

∆λ → observed λ - λ0