Download Day-6

Astronomy 3040
Astrobiology
Spring_2016
Day-6
Homework -1
 Due Monday, Feb. 8
 Chapter 2:
 1, 3, 16
 23, 24, 26
 29, 30, 33
 44
 53, 54, 56
 The appendices will be useful
Project
 http://www.ulalaunch.com/docs/product_sheet/Delt
aIVPayloadPlannersGuide2007.pdf
 This is the Delta-IV payload guide overview. 20MB.
 Planetary quarantine program.
Becoming a Star
 The protostar’s energy source is gravitational energy.
 Temperature rises in the core.
 Hydrogen fusion begins in the core, and the star begins
its life on the main sequence.
 Very low-mass stars (< 0.08 M) never start hydrogen
fusion.
 These are called brown dwarfs.
Protostars
to Stars
Evolutionary Tracks
 An individual star follows an evolutionary track on the
H-R diagram.
 This is the path of the temperature and luminosity with
time.
 Protostars get less luminous and hotter.
 The star first appears as a T Tauri star.
 The star moves on the Hayashi track and arrives on the
main sequence.
 Since L = (area)  (T4), the star contracts.
Star Clusters
 Star formation can make star clusters.
 These are gravitationally bound groups of stars.
 Some stars are more massive, others less so.
 Higher-mass stars evolve faster.
 Clusters are good laboratories for testing our ideas of star
formation and evolution.
Star Clusters and Stellar Evolution
 Star clusters are bound groups of stars, all made at the
same time.
 Each star evolves at a rate set by its mass.
 High-mass stars evolve more quickly.

Young clusters still have massive stars on MS.

In older clusters, massive stars have died.
 Location of main sequence turnoff gives cluster age.
Cluster Trends
Globular clusters (probe halo):
 All old.
 All low in heavy elements.
Open clusters (probe disk):
 Contain dozens to hundreds of stars.
 Clusters are young, old, and in between.
 Rich in heavy elements.
Omega Centaurus
M35
Main Sequence Lifetimes
Mass (M)
Luminosity (L)
17.5
52,500
Lifetime in
billion years
0.01
2.0
14
1.1
1.0
1.0
10
0.67
0.15
53
0.21
0.011
290
Galaxy Formation
 The Milky Way offers clues to galaxy formation.
 All halo stars have some heavy elements, so at least one
prior generation of stars must have existed.
 Halo objects were formed before interstellar gas was all
concentrated into the disk.
 Later star formation was all in the disk.
A Normal Spiral Galaxy
Satellite Galaxies
 The Milky Way probably formed by the merger of many
smaller protogalaxies.
 Several of these are still orbiting the Milky Way as satellite
galaxies.
 These can contain significant amounts of gas.
 The gas delivered by the protogalaxies was a significant
source of star formation.
 Evidence for different chemical evolution timescale.
H-R Diagrams
Compared to the universe, the Earth is less
than a grain of sand on a beach
Our Sun, A Slightly Bigger than most, Star
The Sun is the Largest Object in
the Solar System



The Sun contains more than 99.85% of the
total mass of the solar system
If you put all the planets in the solar system,
they would not fill up the volume of the Sun
110 Earths or 10 Jupiters fit across the
diameter of the Sun
How big is the Sun?
The Sun goes through periods of
relative activity and inactivity
March 5, 2009 21:48:43 CST