Molecular Clouds

Ekta PatelPHYS 2070

October 5th, 2010Instructor: J.West

• 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

Overview

Korista, 2010

Composition & Make-up

• 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

Size• 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

Brightness•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

Location & Distance•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

Origin/Age/Evolution:

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

How They Are Studied•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

Collapse Of A Molecular Cloud•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

Research Study #1

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 supersonic2.) ratio of thermal to magnetic pressure3.) mass-to-magnetic flux ratio is twice the critical 4.) Kinetic and magnetic energies are approximately equal5.) 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

Research Study #2Rapid 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 phase2.) High column density gravitational forces increase3.) 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 quasi-static 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)

 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 Astrophysicshttp://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

Works Cited