Galactic Hazards Flashcards
What is the shape of the milky way?
It has a central bulge and spiral arms of gas and stars in a disk.
How big is the bulge?
10,000 light yeas across
How big is the disk?
100,000 light years diameter
Where is the sun located in the milky way?
Near the plane of the disk at 25,000 light years from the centre
What is the bulge made of?
Old stars, gas and dust
What is the disk made of?
Mostly young stars, gas and dust concentrated in spiral arms
What is the halo made of?
Individual old stars and clusters of old stars and dark matter
Globular clusters
What is the size of the halo?
130,000 light years across
How far away is the Andromeda galaxy?
2.5 million light years
What are the Milky way and andromeda galaxy a part of?
The Local Group which contains 45 other galaxies
What do the milky ways spiral arms contain?
young, hot luminous blue stars which make the arms bright
What is unusal about the solar systems orbit around the centre of the galaxy?
Significantly less elliptical than those of other stars
What does this unique orbit mean?
Prevents it plunging towards the inner galaxy, which has higher cosmic radiation and supernovas
What is unique about solar systems place in the galactic plane?
It has a tilt and lies about 20 light years above the plane
What does the solar system being above the plane mean?
It avoids crossings of the plane so reduces chance of stirring up the Oort cloud and bombarding earth with comets
What is unique about the solar systems angular speed in the galaxy?
Sun is orbiting close to co-rotation radius where angular speed of galaxie’s spiral matches the stars within
What does the angular speed mean for the solar system?
It avoids crossing the spiral arms which would expose earth to supernova and comets
Where have no rocky planets been found?
Around suns with a metallicity of less than 20-30%
What would happen if metallicity was higher in the solar system?
Terrestrial planets would be larger
Stronger gravity
Richer in volatile compounds
Poor in topographic relief
What would the surface look like on these higher metallicity planets?
Ocean planets with extreme weather
What could excess metallicity lead to in the solar system with regards to gas giants?
Increase the number of them and disrupt orbital dynamics
How does metallicity in the Milky way disk change?
Declines with distance
What is metallicity falling at at the suns location?
17%/kpc
Why are outer regions of the galaxy unlikely to have rock planets?
Low abundance of elements beside H and He
Why are the inner regions of the galaxy bad for life?
High supernova rates so rocky planet would be exposed to intense radiation
What is the Galactic Habitable Zone?
Only region where it is believed Earth-like planets can form
What are the counterarguments to galactic constraints?
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
How is the galactic centre a threat to life?
- black hole can turn on releasing burst of high energy radiation - X rays
How can Earth defend against this radiation?
Magnetic field can deflect it
Ozone layer can screen it out
Why are Supernova more of a threat in the inner galaxy?
Higher concentration of older stars
What is the killer radius of a SN?
100 light years
Where is the peak of SN in the galaxy?
60% of the suns distance from the galactic centre
How often do SN occur in our galaxy?
1 per 40 years generally
Six in past 1,000 years in out galaxy
How often does a SN occur within 33ly of Earth?
Every 240 Million years
From passing through galactic plane
How many star systems within 15kpc of us?
50
What are gamma ray bursts?
Most powerful explosion observed since the BB
What could a GRB within a few kpc do to Earth?
Deplete the ozone layer allowing increase in solar UV to reach the surface which would damage life
What could a GRB do to humans?
Pass through our bodies and cause damage to tissue and DNA
When did most GRBs happen?
Early universe
How could GRBs have affected Mars?
Mars has no atmospheric shielding
