Mississauga Centre RASC

76th Meeting

Speaker’s’ Night

Day:                January 12, 2007

Speaker:     Norman Murray

Roy Swanson spoke about the sky tonight touching upon Comet McNaught, planets Venus, Mars and Jupiter.                      

Dust and Feedback in Infrared Galaxies

Norman Murray is the director of the Canadian Institute for Theoretical Astrophysics, housed in the McLennan Building at U of T. His research centers on galaxies and quasars.

Ultraluminous infrared galaxies have rapid star formation wherein 100 solar masses of gas per year are turned into stars over a period of 100 million years.  The mass of the central black hole in such a galaxy can be ascertained by measuring the orbital velocity of stars about it.  Because of distribution of mass, the velocity of stars remains fairly similar  regardless of distance from the centre. In a spiral galaxy, most of the mass is in the form of dark matter.  In an elliptical, most of the mass is in stars, and the velocity dispersion is related to the luminosity of the galaxy.  The Faber-Jackson relation states that the luminosity of the galaxy varies as the fourth power of the dispersion. 

Dr. Murray showed an image of galaxy M82. Most of the outflow of gas, 4 solar masses per year, is driven by star formation in the centre.  Rapidly star forming galaxies have evidence of outflow from supernovae. The hot gas at 10⁷  K moves at 500 km/sec and is accompanied by cold gas moving at 30-40 km/sec and by dust which absorbs photons and escapes from the galaxy. 

Ultraluminous infrared galaxies,  the most luminous galaxies in the universe with 10¹² the luminosity of the Sun  (Milky Way is 10¹⁰ ) have large quantities of dust.  The dust made inside massive stars implies star formation. Blue shifted sodium shows an outflow of 400 to 500 km/sec. The efficient transport of angular momentum in mergers of galaxies can trigger black hole growth and active galactic nuclear activity.

Dust absorbs the radiation produced in starbursts or active galactic nuclei and dust is also collisionally coupled to the gas with the result that both gas and dust blow out of a galaxy. If the radiative force is greater than the force of gravity, gas will be expelled. As gas is driven out, star formation decreases.  Star and gas formation reach a steady state with gas escape.  Radiation pressure can thus drive powerful galactic winds and is an important feedback mechanism in the growth of galaxies and black holes.  It can also account for the properties of cold outflowing gas seen in starbursts.

Observing course

Ian McGregor described the proposed observing course which will be tied into the observing certificate of the RASC.

Mars Reconnaissance Observer

Randy Attwood showed images taken by the MRO of the 10 year old Pathfinder Sojourner and the rock “Yogi”.  Randy also spoke about the upcoming TV program “Zero Hour – Columbia – Falling Star”  regarding the demise of the space shuttle Columbia.

Submitted by Chris Malicki, Secretary  Chris Malicki, Secretary                               back to Miss Centre. meeting reports page
Mississauga Centre RASC