Ekta Patel PHYS 2070 October 5 th, 2010 Instructor: 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

Until the 70’s regarded as “abnormally dense interstellar clouds”. A dense cloud containing ~90% hydrogen (H 2 ) & 10% helium. Molecules are abundant not atoms Kelvin. Densities as high as particles/m. Main constituents: –Molecules –Dust grains –ions

Most massive object in our galaxy Typically solar masses MC that exceeds 10 6 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 100 o 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 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 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 3 rd ed. 9: New York: Cambridge University Press Goldsmith D, Owen T. Different Types of Molecular Clouds. The Search for Life in the Universe 3 rd ed. 3: Sausalito: University Science Books Publishers Lada CJ, Kylafis ND. Physical Conditions In Nearby Molecular Clouds: The Origin of Stars and Planetary Systems 2: Dordrecht: Kluwer Academic Publishers Chaisson E, McMillan S. The Interstellar Medium: Astronomy Today 6 th ed. 18: Sanfansico. Jim Smith Publishing Journal Article: Ballesteros-Paredes J, Bergin EA, Hartmann L, et al Rapid Formation of Molecular Clouds and Stars in the Solar Neighborhood: ApJ Cruther MR, Magnetic Fields in Molecular Clouds: Observations Confront Theory: ApJ Web Page Daou D, Hermans-Killam L.Thaller M,. et. Al Molecular Clouds Korista K. PHYS 3250: An Introduction to Astrophysics The Internet Encyclopedia of Science, Giant Molecular Clouds: Wikipedia, et. Al Orion Molecular Cloud Complex Works Cited