The Milky Way

Question 1

What does the Milky Way indicate?

Answer 1

That we live inside a flattened (disc) system of stars

Question 2

Describe the shape of the Milky Way

Answer 2

•a thin disc
•up to 100000Ly disc diameter
•sun is 28000Ly from its centre
•at sun it is 1000ly thick as more near centre

Question 3

How many stars does Milky Way contain?

Answer 3

About 100 billion

Question 4

How much do most mw stars weigh compare to sun?

Answer 4

Most about half as heavy

Question 5

How much does interstellar gas weigh in comparison to stars?

Answer 5

Weighs about 10% as much as

Question 6

What are the 3 main groupings of stars in the Milky Way?

Answer 6

•bulge-round central core
•disc-flat exterior spiral
•halo-sphere surrounding other components

Question 7

Describe the disc

Answer 7

•contributes 80% of total light
•diameter of 100KLy
•star ages from 0-10Gyr
•high metal content
•orbits of stars circular

Question 8

Describe the Bulge

Answer 8

•contributes 15% of total light
•diameter of 10KLy
•star ages around 10Gyr
•moderate metal content
•random orbit of stars

Question 9

Describe the halo

Answer 9

•contributes 5% of total light
•diameter of 300Kly
•star ages >10Gyr
•very low metal content (0.01Z)
•random orbit of stars

Question 10

Why does metal content indicate age of star?

Answer 10

Metals made in stars so earliest stars had none. Later generations formed from clouds that included remnants of exploded earlier ones

Question 11

What are the two varieties of star clusters?

Answer 11

Open and globular

Question 12

Where did star clusters form from?

Answer 12

A single gas cloud all at once

Question 13

What can we tell about a cluster by looking at their bluest star?

Answer 13

•intrinsic brightness, work distance
•age

Question 14

Describe an open cluster

Answer 14

•typical age of <5Gyr
•metal content around 1Z
•100-10000 stars
•irregular shape
•1200 known clusters in mw
•located in disc

Question 15

Describe a globular cluster

Answer 15

•typical age >10Gyr
•metal content <0.1Z
•10^6 stars
•smooth spherical shape
•known 150 clusters in mw
•located in halo and bulge

Question 16

Why do globular clusters stay tightly bound?

Answer 16

Due to conditions in early universe, so do not break apart like open clusters appear to be doing

Question 17

Explain steps of bubble formation

Answer 17

•massive stars give off powerful stellar winds, ejecting gas from their outer atmosphere
•when they supernova, remaining mass ejected
•shockwave compresses surrounding gas, creating bubbles and super-bubbles of ionized and hot gas

Question 18

What is the mw nearest large neighbour?

Answer 18

Andromeda, 2.6Ly away

Question 19

What are some nearby satellite dwarf galaxies?

Answer 19

Small and large Magellanic Clouds and Sagittarius dwarf

Question 20

What is galactic cannibalism and give example?

Answer 20

Process of larger galaxy absorbing smaller galaxy. MW absorbing Sagittarius dwarf

Question 21

What are stellar streams?

Answer 21

•wide streams of stars trailing out
•wake of stars from dwarf galaxies and clusters being torn apart by MW gravity

Question 22

What happened to gas clouds in primordial universe?

Answer 22

Collapsed under gravity into early mini galaxies (formed stars then collected together into larger clouds)

Question 23

What happened to the gas and dust in Proto-MW?

Answer 23

Collapses onto the plane forming more stars and the disc

Question 24

What may have caused the bulge?

Answer 24

•mergers(dwarf galaxies falling onto disc and disrupting)
•evolved from central part of disc

Question 25

What mixed into the disc to form atomic clouds?

Answer 25

Gas from supernova and winds

Question 26

Why has star formation oscillated over time?

Answer 26

Mix of internal dynamics and interactions

Question 27

How long will stars form in mw for?

Answer 27

> 5 billion more years

Question 28

What lies at the core of the galaxy?

Answer 28

Sagittarius A* (a bright radio source)

Question 29

What causes rapidly moving stars at central light year?

Answer 29

A Super-massive black hole