useful books: carroll and ostlie “intro to modern astrophys”, prialnik “intro to stellar...

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...

Su

n i

s ra

dia

tive

exc

ept

for

a th

in s

ub

surf

ace

la

yer

10 s

ola

r m

ass

sta

r h

as c

on

vcti

ve

core

an

d r

adia

tiv

e en

velo

pe

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