Ekta Patel
PHYS 2070
October 5th, 2010
Instructor: J.West
Overview
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Composition & make-up
Size
Brightness
Location & Distance
Origin/Age/Evolution
How they are studied
Collapse of a molecular cloud
Research Study #1
Research Study #2
Works Cited
Korista, 2010
• Until the 70’s regarded as “abnormally dense interstellar clouds”.
• A dense cloud containing ~90% hydrogen (H2) & 10% helium.
• Molecules are abundant not atoms.
• 10-20 Kelvin.
• Densities as high as 1012 particles/m.
• Main constituents:
– Molecules
– Dust grains
– ions
•Most massive object in our
galaxy
•Typically 100-106 solar masses
•MC that exceeds 106 are
Giant Molecular Clouds
•100 pc across
•Irregular shape: blobs &
filaments
•Occupy same space as a diffuse
cloud
Wikipedia. 2010
•Typically noticed due to the
fact that they block starlight
from background stars
•Light present from star
forming region dependent
upon location:
•Within field of view
•Opposite side
•Embedded within
molecular cloud
Daou, et. Al. 2009
•Closest are within a few
hundred pc
•Orion Molecular Cloud
•Typically found within the
plane of the galaxy
•Most clouds clumped in
spiral arms of the disk
•Usually around latitudes
of 100o of the galactic
centre
Daou, et. Al. 2009
Certain number of stars are formed  stars heat
surrounding gas  molecules break up  gas dissipates
M.C.’s colliding with galaxies experience it a little
differently
-collision causes rapid star formation which uses up
most of the gas, before it can get hot and dissipate
-Short life Jeans mass
•Use of spacecraft  measures UV
radiation of stars
•Observation of other molecules 
effective in studying the
interior of molecular clouds
•Rotation Properties  aids in
spectral identification
Wikipedia. 2010
•Formation site of all
known young stars
•primarily in GMC
•Host stars in different
stages
•Host stars in different
ranges
•Masses of stars range from
0.1-30 solar masses
Wikipedia. 2010
Magnetic Fields in Molecular Clouds: Observations Confront Theory
Purpose: calculate/observe measurements of magnetic field strengths
in a molecular cloud
Findings: 1.) Internal motions are supersonic
2.) ratio of thermal to magnetic pressure
3.) mass-to-magnetic flux ratio is twice the critical
4.) Kinetic and magnetic energies are approximately equal
5.) The magnetic field strengths scale incorporating gas density
Summary: The various measurements carried out suggest that
magnetic field strength in molecular clouds is a very important part of
the physics behind star formation and cloud evolution.
Cruther. 2003
Rapid Formation of Molecular Clouds and Stars in the Solar Neighborhood
Purpose: “Show how molecular clouds in the solar neighborhood might be
formed and produce stars rapidly enough to explain stellar population ages”
(Lee, et al. 2001)
Findings: 1.) A lot of the accumulation of clouds near the solar circle might
occur in the atomic phase
2.) High column density  gravitational forces increase
3.) Magnetic field is [usually] not strong enough to allow for a cloud to rapidly
form and then collapse.
4.) Dispersal of gas, passing shock waves, reduction of shielding --> limit length
of star formation epoch
Summary: Placing a high importance on the boundary conditions that come into
play when working to decipher molecular cloud formation. Instead of a quasistatic process, it is implied that star formation is highly dynamic and thus that
when low galactic star formation rates are low, it is due to low levels of
efficiency and not a slower collapse in the respected region.
•(Ballesteros-Paredes , et al. 2001)
Works Cited
Books:
Burke BF, Graham-Smith F. Dense Molecular Clouds. Radio Astronomy 3rd ed. 9: 191-192 New York: Cambridge University Press
Goldsmith D, Owen T. Different Types of Molecular Clouds. The Search for Life in the Universe 3rd ed. 3: 59-63. Sausalito:
University Science Books Publishers
Lada CJ, Kylafis ND. Physical Conditions In Nearby Molecular Clouds: The Origin of Stars and Planetary Systems 2: 69-71.
Dordrecht: Kluwer Academic Publishers
Chaisson E, McMillan S. The Interstellar Medium: Astronomy Today 6th ed. 18: 495-497. Sanfansico. Jim Smith Publishing
Journal Article:
Ballesteros-Paredes J, Bergin EA, Hartmann L, et al. 2001. Rapid Formation of Molecular Clouds and Stars in the Solar
Neighborhood: ApJ 562-2
Cruther MR, Magnetic Fields in Molecular Clouds: Observations Confront Theory: ApJ 520-2
Web Page
Daou D, Hermans-Killam L.Thaller M, . et. Al. 2008 Molecular Clouds
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/molecular_clouds.html
Korista K. PHYS 3250: An Introduction to Astrophysics
http://homepages.wmich.edu/~korista/phys325.html
The Internet Encyclopedia of Science, Giant Molecular Clouds:
http://www.daviddarling.info/encyclopedia/G/giant_molecular_cloud.html
Wikipedia, et. Al. 2010 Orion Molecular Cloud Complex http://en.wikipedia.org/wiki/Orion_Molecular_Cloud_Complex