APS 5740: INTERSTELLAR ASTROPHYSICS

The image at left, taken with the Hubble Space Telescope, shows a region in the Tarantula Nebula, a giant HII region (also known as 30 Doradus) in the Large Magellanic Cloud. (Click on the image for a larger version.) The nebula is powered by the most luminous star-forming region in the local universe, a cluster of young stars known as R136. The field shown here lies about 45 pc from R136 and the center of the nebula. The interstellar medium in this region is violently disturbed, with large velocities and spectral evidence of shocks as well as photoionization. Visible in the lower right is another cluster of luminous, massive stars, denoted Hodge 301. With an estimated age of 20 million years, Hodge 301 is 5-6 times older than the R136 cluster, and several of the most massive cluster stars have probably exploded as supernovae. The blast waves and ejecta from these supernovae shock and compress the surrounding gas of the nebula, producing the sheets and filaments visible throughout the image. Dense, dark globules of gas and dust are also visible (especially near the center of the image) and may represent future sites of star formation.


Spring 2000

Instructor: Phil Maloney
Schedule: MWF 10:00-10:50, in G1B39

Course Description

The interstellar medium - the gas, dust, energetic particles, and magnetic fields that lie in the vast interstellar spaces between the stars - plays a fundamental role in the evolution of stars and galaxies. The ISM is the raw material from which stars form, and thus the physical conditions in the interstellar medium determine the star formation rate (both local and global) within galaxies. The formation of stars in turn influences the physical and dynamical state of the ISM, as energy, mass and momentum are injected into the ISM by stars as they evolve, through radiation, stellar winds, and supernovae.

The Ring Nebula, NGC 7027, in the constellation Lyra. This is a beautiful example of a planetary nebulae.
The physical conditions in the interstellar medium cover an enormous range, from cold (T ~ 10 K), dense, molecular clouds to hot (T ~ several million K), low-density ionized gas. In addition, there are relativistic particles (cosmic rays and relativistic electrons), magnetic fields, and dust particles of varying size and temperature. The ISM can both highlight sources of energy, e.g., photoionized nebulae such as HII regions and planetary nebulae, which are often far more prominent than the stellar radiation sources themselves, and obscure them, as in dense star-forming molecular clouds, in which young stellar and proto-stellar objects may be completely enshrouded by the surrounding gas and dust, so that the stellar luminosity emerges only at infrared and radio wavelengths. This huge range in the physical conditions means that the characteristics of the radiation emitted by the ISM also vary enormously: the typical wavelength of radiation varies from about 100Å for hot low-density gas, to a few thousand Å for gas photoionized and heated by hot stars, to fractions of a millimeter for cold molecular clouds. Hence a broad knowledge of atomic and molecular physics, and their application to extremely unusual (by terrestrial standards) physical conditions (e.g., enormous deviations from thermodynamic equilibrium) is required to interpret observations of the interstellar medium.

NGC 3603, an HII region surrounding a young, very dense stellar cluster, with massive O and Wolf-Rayet stars. Radiation and winds from the luminous young stars have blown a cavity in the surrounding interstellar gas.
Interstellar Astrophysics (APS 5740) is a graduate-level course that is taught every two years. The emphasis is on physical processes occurring in the interstellar medium, rather than on reviewing data; however, the main goal is to provide an overview of our current understanding of the structure and dynamics of the ISM (aspects of which we can expect to advance markedly in the next year or so as data from the FUSE mission begin to appear.) There will be some overlap with APS 5110, Internal Processes I, which is a prerequisite for APS 5740 (this prerequisite can be waived with the consent of the instructor); however, it is intended that the course will be largely self-contained. A large fraction of the course grade will be based on regular problem sets; in addition, there will be a couple of somewhat more involved computational projects. There will be no exams.

Two textbooks will be used in the course: Spitzer's classic Physical Processes in the Interstellar Medium (fortunately now available in a semi-reasonably priced paperback edition) and Osterbrock's nearly-as-classic Astrophysics of Gaseous Nebulae and Active Galactic Nuclei, which is a very reasonably priced hardcover. A number of other books may be very useful as references, in particular Rybicki & Lightman's Radiative Processes in Astrophysics (and although I would recommend this book for anyone planning on a career in astrophysics, the paperback edition is considerably overpriced; a copy will be on reserve in the library), and the three volumes (especially the first two) of the Teton conferences on the interstellar medium. An outline of the intended course material is given in the syllabus below. This may change somewhat over the next couple of months, as I'm still developing the course.


Syllabus

A stunning image of the Rosette Nebula in Monoceros, taken by Travis Rector and collaborators using the Mosaic Camera on the 0.9m telescope on Kitt Peak. The hot blue stars in the center are responsible for ionizing the gas and clearing the central hole (through the action of stellar winds). Red, blue, and green correspond to emission from hydrogen, sulfur, and oxygen, respectively.
A small portion of the Cygnus Loop, the remnant of a supernova that exploded about 15,000 years ago. Red, blue and green correspond to emission in lines of sulfur, oxygen, and hydrogen, respectively.



All of the images on this page - except for the Rosette Nebula - were obtained using the Hubble Space Telescope. More beautiful images await you on the HST web page.

But don't stop there: while you're at it, check out the Chandra X-Ray Observatory home page.

The Rosette image was obtained using the 0.9m Telescope at Kitt Peak National Observatory, run by the National Optical Astronomy Observatories. This image is copyright Association of Universities for Research in Astronomy Inc. (AURA), all rights reserved. More stunning images can be found in the NOAO Image Gallery.

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