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Life in the Cosmos > Galactic Hazards > Flashcards

Galactic Hazards Flashcards

1
Q

What is the shape of the milky way?

A

It has a central bulge and spiral arms of gas and stars in a disk.

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2
Q

How big is the bulge?

A

10,000 light yeas across

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3
Q

How big is the disk?

A

100,000 light years diameter

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4
Q

Where is the sun located in the milky way?

A

Near the plane of the disk at 25,000 light years from the centre

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5
Q

What is the bulge made of?

A

Old stars, gas and dust

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6
Q

What is the disk made of?

A

Mostly young stars, gas and dust concentrated in spiral arms

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7
Q

What is the halo made of?

A

Individual old stars and clusters of old stars and dark matter
Globular clusters

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8
Q

What is the size of the halo?

A

130,000 light years across

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9
Q

How far away is the Andromeda galaxy?

A

2.5 million light years

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10
Q

What are the Milky way and andromeda galaxy a part of?

A

The Local Group which contains 45 other galaxies

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11
Q

What do the milky ways spiral arms contain?

A

young, hot luminous blue stars which make the arms bright

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12
Q

What is unusal about the solar systems orbit around the centre of the galaxy?

A

Significantly less elliptical than those of other stars

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13
Q

What does this unique orbit mean?

A

Prevents it plunging towards the inner galaxy, which has higher cosmic radiation and supernovas

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14
Q

What is unique about solar systems place in the galactic plane?

A

It has a tilt and lies about 20 light years above the plane

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15
Q

What does the solar system being above the plane mean?

A

It avoids crossings of the plane so reduces chance of stirring up the Oort cloud and bombarding earth with comets

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16
Q

What is unique about the solar systems angular speed in the galaxy?

A

Sun is orbiting close to co-rotation radius where angular speed of galaxie’s spiral matches the stars within

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17
Q

What does the angular speed mean for the solar system?

A

It avoids crossing the spiral arms which would expose earth to supernova and comets

18
Q

Where have no rocky planets been found?

A

Around suns with a metallicity of less than 20-30%

19
Q

What would happen if metallicity was higher in the solar system?

A

Terrestrial planets would be larger
Stronger gravity
Richer in volatile compounds
Poor in topographic relief

20
Q

What would the surface look like on these higher metallicity planets?

A

Ocean planets with extreme weather

21
Q

What could excess metallicity lead to in the solar system with regards to gas giants?

A

Increase the number of them and disrupt orbital dynamics

22
Q

How does metallicity in the Milky way disk change?

A

Declines with distance

23
Q

What is metallicity falling at at the suns location?

A

17%/kpc

24
Q

Why are outer regions of the galaxy unlikely to have rock planets?

A

Low abundance of elements beside H and He

25
Q

Why are the inner regions of the galaxy bad for life?

A

High supernova rates so rocky planet would be exposed to intense radiation

26
Q

What is the Galactic Habitable Zone?

A

Only region where it is believed Earth-like planets can form

27
Q

What are the counterarguments to galactic constraints?

A

A very low metalliticity could be enough to make one earth like planet
We dont know if SN radiation is fatal for life as atmosphere could protect it

28
Q

How is the galactic centre a threat to life?

A
  • black hole can turn on releasing burst of high energy radiation - X rays
29
Q

How can Earth defend against this radiation?

A

Magnetic field can deflect it
Ozone layer can screen it out

30
Q

Why are Supernova more of a threat in the inner galaxy?

A

Higher concentration of older stars

31
Q

What is the killer radius of a SN?

A

100 light years

32
Q

Where is the peak of SN in the galaxy?

A

60% of the suns distance from the galactic centre

33
Q

How often do SN occur in our galaxy?

A

1 per 40 years generally
Six in past 1,000 years in out galaxy

34
Q

How often does a SN occur within 33ly of Earth?

A

Every 240 Million years
From passing through galactic plane

35
Q

How many star systems within 15kpc of us?

A

50

36
Q

What are gamma ray bursts?

A

Most powerful explosion observed since the BB

37
Q

What could a GRB within a few kpc do to Earth?

A

Deplete the ozone layer allowing increase in solar UV to reach the surface which would damage life

38
Q

What could a GRB do to humans?

A

Pass through our bodies and cause damage to tissue and DNA

39
Q

When did most GRBs happen?

A

Early universe

40
Q

How could GRBs have affected Mars?

A

Mars has no atmospheric shielding

Life in the Cosmos (18 decks)

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