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Astro 150 Spring 2005: Lecture 14 page 1
Reading: Chapter 17 (17.1-17.4)Exam 2:
Thursday March 24
th
Review of last time: Stellar Evolution & Star ClustersThe Mass Luminosity Relation
the Vogt-Russell Theorem Main Sequence Lifetimes
lifetime shorter for massive stars (t ~1/M
massive stars burn out fasterstars
evolve
slowly
Astro 150 Spring 2005: Lecture 14 page 2
Reading: Chapter 17 (17.1-17.4)Exam 2:
Thursday March 24
th
Review of last time: Stellar Evolution & Star ClustersKey Objects – Star Clusters
compact grouping of stars formed at the same timetypes of clusters
associations - all main sequence, including O,Bopen clusters - no O,B - and some red giantsglobular clusters - low mass MS stars, lots of giants age of cluster given by most massive MS star remainingoldest clusters: 13 billion years old
Astro 150 Spring 2005: Lecture 14 page 3
Formation of Stars
Evidence from the Stars
see massive stars that must have formed recently
Astro 150 Spring 2005: Lecture 14 page 4
Formation of Stars
Evidence from the Stars
see massive stars that must have formed recentlysee available raw material – dust and gas
Astro 150 Spring 2005: Lecture 14 page 5
Formation of Stars
Evidence from the Stars
see massive stars that must have formed recentlysee available raw material – dust and gassee stars that are embedded in dust and gas Optical – ISU Fick Observatory
IR – Spitzer Space Telescope
Astro 150 Spring 2005: Lecture 14 page 6
Formation of Stars
Evidence from the Stars
see massive stars that must have formed recentlysee available raw material – dust and gassee stars that are embedded in dust and gassee disks, jets associated with these stars
Astro 150 Spring 2005: Lecture 14 page 7
Stars form in cold, dense regionscalled molecular clouds
Average Interstellar medium (ISM) conditions:
density: a few atoms / cc (air: 10
18
atoms/cc)
temperature ~ 100Kcomposition: 75% hydrogen
Molecular Clouds: clumps of interstellar medium (ISM)
density: up to 10
4
/ cc
mass: up to 10
6
Msun
radius ~ 10 - 30 pctemperature ~ 10Kcomposition:
dustmolecules H
, H 2
O, CO 2
NH
CH 2
COOH (amino acids) 2
C
H 2
OH (ethanol)... 5
Astro 150 Spring 2005: Lecture 14 page 8
often associated with young star cluster -
stellar nurseries!
Optical (H
α
(3-2) emission)
CO emission (mm waves)
shows us H
2
location
This region is about 80 pc long with~ 100 000 solar masses of material!
Astro 150 Spring 2005: Lecture 14 page 13
Astro 150 Spring 2005: Lecture 14 page 14
First phase: from cloud to protostar
Infalling material around protostars forms a disk:
Why? – conservation of angular momentum
Astro 150 Spring 2005: Lecture 14 page 15
Second phase: evolution
to the main sequence
Pre-main sequence stars – hotter, more luminousbut no fusion reactions in core
Eventually most of theinfalling material isassembled into acompact, dense region.
Astro 150 Spring 2005: Lecture 14 page 16
Second phase: evolution
to the main sequence
Stellar winds and jets clear remaining material:
Pre-main sequence star eventually becomes visible T-Tauri Stars
•cool stars with
irregular brightness •blowing away
surrounding dust •evidence of
surrounding
disk
•around a solar mass•More massive stars may never becomevisible before reachingthe main sequence
Astro 150 Spring 2005: Lecture 14 page 17
Second phase: evolution
to the main sequence
Star continues to contractuntil core temperature ishot enough to allow fusion.Hydrostatic equilibrium isestablished & fusion ratebalances energy loss rateStar becomes a hydrogen“burning” main sequencestar.
Astro 150 Spring 2005: Lecture 14 page 18
Second phase:
evolution to the main sequence
Star disperses anyremaining material.One way a star can do thisis through the formation ofplanets.We have detected planetsaround other nearby solartype stars (5-10% rate).About 130 planets in total.
Astro 150 Spring 2005: Lecture 14 page 19
The timing…
Very Fast 10
5
years
Evolution to MS depends on mass
Astro 150 Spring 2005: Lecture 14 page 20
The timing…
For all stars this is a VERY SHORT time
(e.g. Sun < 100 million years after initial collapse)
