Interstellar Medium (ISM)• Read Your Textbook: Foundations of Astronomy
– Chapter 11, 12
• Homework Problems Chapter 11– Review Questions: 1, 2, 5, 6– Review Problems: 2-6– Web Inquiries: 1
• Homework Problems Chapter 12– Review Questions: 2, 3, 8, 9– Review Problems: 3, 7-9 (old 1, 4-7)– Web Inquiries: 1
A Galaxy Rich in Gas and Dust
ISMThe bright regions are congregations of innumerable stars.
However, the dark areas are not simply "holes" in the stellar
distribution. They are regions of space where interstellar
matter obscures the light from stars beyond.
Their very darkness means that they
cannot be easily studied by optical
methods used for stellar matter.
There is, quite simply, very little to
see in visible light!
Gas and DustIdentical regions of space in the optical and infrared.
NebulosityStar formation regions are rich in gas and dust.
AbsorptionAbsorption
of starlight
by the ISM
causes
interstellar
reddening.
ExtinctionProbing the ISM by
examining absorption
lines in stellar spectra
caused by intervening
clouds.
ISM Characteristics
21-cm Radio Emission
21-cm Radio Energy Transition
21-cm Milky Way
ISM CompositionAlso popular cometary chemical composition list.
Gravitational CollapseStar formation begins when gravity begins to dominate over
heat, causing a cloud to lose its equilibrium and start to
contract.
Only after the cloud has undergone radical changes in its
internal structure is equilibrium finally restored.
Protostar Disk
Orion Nursery
Star Formation Regions
Cloud ShockWave
Cloud FragmentationStar formation usually involves creating “clusters” of stars.
Open Cluster• Thousands of stars, sometimes gravitationally bound
• Contain the youngest, hottest galactic stars
• Associated with star formation regions in the galaxy.
Globular Cluster• Hundreds of thousands of stars, gravitationally bound and
spherically symmetric.
• Contain the oldest galactic stars
• Symmetrically distributed
about the galaxy.
ProtoStar Tracks
Protostar Stages
Hyashi Tracks
Gravity Versus Pressure
Stellar Structure Laws