The Milky Way Flashcards
What does the Milky Way indicate?
That we live inside a flattened (disc) system of stars
Describe the shape of the Milky Way
•a thin disc
•up to 100000Ly disc diameter
•sun is 28000Ly from its centre
•at sun it is 1000ly thick as more near centre
How many stars does Milky Way contain?
About 100 billion
How much do most mw stars weigh compare to sun?
Most about half as heavy
How much does interstellar gas weigh in comparison to stars?
Weighs about 10% as much as
What are the 3 main groupings of stars in the Milky Way?
•bulge-round central core
•disc-flat exterior spiral
•halo-sphere surrounding other components
Describe the disc
•contributes 80% of total light
•diameter of 100KLy
•star ages from 0-10Gyr
•high metal content
•orbits of stars circular
Describe the Bulge
•contributes 15% of total light
•diameter of 10KLy
•star ages around 10Gyr
•moderate metal content
•random orbit of stars
Describe the halo
•contributes 5% of total light
•diameter of 300Kly
•star ages >10Gyr
•very low metal content (0.01Z)
•random orbit of stars
Why does metal content indicate age of star?
Metals made in stars so earliest stars had none. Later generations formed from clouds that included remnants of exploded earlier ones
What are the two varieties of star clusters?
Open and globular
Where did star clusters form from?
A single gas cloud all at once
What can we tell about a cluster by looking at their bluest star?
•intrinsic brightness, work distance
•age
Describe an open cluster
•typical age of <5Gyr
•metal content around 1Z
•100-10000 stars
•irregular shape
•1200 known clusters in mw
•located in disc
Describe a globular cluster
•typical age >10Gyr
•metal content <0.1Z
•10^6 stars
•smooth spherical shape
•known 150 clusters in mw
•located in halo and bulge
Why do globular clusters stay tightly bound?
Due to conditions in early universe, so do not break apart like open clusters appear to be doing
Explain steps of bubble formation
•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
What is the mw nearest large neighbour?
Andromeda, 2.6Ly away
What are some nearby satellite dwarf galaxies?
Small and large Magellanic Clouds and Sagittarius dwarf
What is galactic cannibalism and give example?
Process of larger galaxy absorbing smaller galaxy. MW absorbing Sagittarius dwarf
What are stellar streams?
•wide streams of stars trailing out
•wake of stars from dwarf galaxies and clusters being torn apart by MW gravity
What happened to gas clouds in primordial universe?
Collapsed under gravity into early mini galaxies (formed stars then collected together into larger clouds)
What happened to the gas and dust in Proto-MW?
Collapses onto the plane forming more stars and the disc
What may have caused the bulge?
•mergers(dwarf galaxies falling onto disc and disrupting)
•evolved from central part of disc
What mixed into the disc to form atomic clouds?
Gas from supernova and winds
Why has star formation oscillated over time?
Mix of internal dynamics and interactions
How long will stars form in mw for?
> 5 billion more years
What lies at the core of the galaxy?
Sagittarius A* (a bright radio source)
What causes rapidly moving stars at central light year?
A Super-massive black hole
