useful books: carroll and ostlie “intro to modern astrophys”, prialnik “intro to stellar...
TRANSCRIPT
Useful books: Carroll and Ostlie “IntroTo Modern Astrophys”, Prialnik “Intro to Stellar Stuct. & Evol.”
Jeans instability & the collapse of molecular clouds
James Hopwood Jeans (1877-1946)
Oph Giant Molecular Cloud, 160 pc awaycontains numerous dark clouds
OphV380 Ori + NGC1999
GMCs contain: dark clouds, cores, Bok globulesGMC mass / solar mass ~ 105
Dark clouds
L57 Barnard 68
Jeans mass
Jeans mass
Following the fragmentation history, and tracking theway M_Jeans changes w.r.t. the fragment mass, Hoyle (1953) arrived at a concept of opacity-limited fragmentation. When heat gets trapped by opacity, Jeans massincreases because T raises.
The smalles mass of fragment is ~0.01 M_sun = 10 m_jup
Hayashi tracks and thePre-Main Sequenceevolution of stars
Chushiro Hayashi (1920-2010 )
Log T_eff
Log L
H-R diagram
Hayashi theory gives a nice explanation for ~vertical tracks of PMS objectsin the H-R diagram, however we need to make certain assumptions/guesses
Hayashi phase ofprotostar contraction
Star formation in reality is a bit different: e.g., no spherical symmetry!
Glenn Schneider
NICMOS ProjectSteward Observatory
HUBBLE SPACE TELESCOPE
file:/starsrus.as.arizona.edu/BIG/EONS_PROGRAM_OVERVIEW/CANDIDATES_EVOLUTION.VG G. Schneider, 7/09/2000
Evolution of M Dwarf Stars, Brown Dwarfsand Giant Planets
(from Adam Burrows)
-10
-8
-6
-4
-2
0
6 7 8 9 10Log10 Age (years)
Log
10 L
/Lsu
n 80Mjup
14Mjup
JUPITER
SATURN
STARS (Hydrogen burning)
BROWN DWARFS (Deuterium burning)
PLANETS
200Mjup
GL
503.2B
GL
577B/C
HR
7329B
CD
-33° 7795BT
WA
6B ?
Which regions of a star are convective and which radiative?
That depends on mass...
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M/M_sun
UKAFF (UK Astroph. Fluids Facility) supercomputer (parallel computer)
Stars are forming in…these boxes.
Matthew Symmetric initial conditionsBate(1998)
Realistic star formation simulations using Smoothed Particle Hydrodynamics became possible
several years ago.
(Up to) millions of particles represent a moving, irregular, 3-D grid, and can be thought of as gas clouds
that partially overlap. Each particle interacts with 10…50 neighbors to represent
pressure forces with good accuracy.
A somewhat ad hoc treatment also endows gas with viscosity.
The gas is self-gravitating.
Matthew Bate(2003), Bate and Benz (2003)SPH, 1.5M particles
starting from turbulentgas cloud
collapse starts after turbulence dies downand Jeans mass drops below the cloud mass.
Brown dwarfs - a failedattempt at stardom
As seen in the simulation of molecular cloud fragmentation,brown dwarfs (smallest objects simulated as white points) form in large numbers, and are mostly dispersed throughout the Galaxy afterwards. Sometimes, they are foundas orbital companions to stars (not frequently, hence the term “brown dwarf desert” by comparison with the large numbersof planetary companions to stars.)
And there is even one BD with it’s own companion of only 5 Jupiter masses!
5 M_jup planet around a 25 M_jup Brown Dwarf in 2MASS1207
A strange system discovered in 2003 (among other by RayJayawardhana from UofT) :
ESO/VLT AO HST/NICMOS, 1.6um
BD image has been removed by observational technique
Disks - a natural way to stardomAs seen in the simulation of molecular cloud fragmentation,star formation is very non-spherical and not even very axisymmetric: it is 3-D and leads to protostars surrounded byaccretion disks. The main physical reason is the angular momentum (L)conservation: before L is transferred outward (e.g. by viscosity), the gas cannot approach the rotation axis; but it has no such restriction on approaching the equatorial plane (or midplane), where it gathers in the form of a rotationally-supported thin disk.
disk
R ~ 200 AU