Winter School of the ISM 2009 > Lectures
Last update: February 27, 2009
Aharonian: [1, 2] [3] [4] [5][updated on the 24th]
Bernard: [1] [2] [3] [4][updated on the 27th]
Heyer: [1] [2] [3] [4] [updated on the 26th]
Dubner: [1] [2] [3] [4][updated on the 27th]
Felix Aharonian (Max-Planck-Institut fur Kernphysik/Dublin Institute for Advanced Studies)
I will discuss very high energy phenomena which take place in astrophysical environments on different scales - from compact objects like black holes and neutron stars/pulsars to giant radiogalaxies and clusters of galaxies. The course will consist of 4 lectures:
Jean-Philippe Bernard (Centre d'Etude Spatiale des Rayonnements)
This lecture will review our current knowledge about dust in space. It will include absorption and scattering by dust particles, emission by dust, both transient (small grains and PAH) and at thermal equilibrium (large grains). I will also discuss spinning dust emission and polarization of the absorbed and emitted light by grains aligned with the magnetic field.
I will also address important processes where dust is involved, such as the formation of molecules, the photo-electric heating of the gas and the formation and destruction of dust in space. All aspects will be illustrated by observational results of dust in the solar system, in the Milky Way, and nearby Galaxies.
If time allows, I will present the Herschel and Planck space missions which will be launched this year, and which should greatly improve our knowledge in this field.
Mark Heyer (University of Massachusetts)
The transformation of interstellar gas into stars plays a key role throughout astrophysics -- from the formation of the Solar System and extra-solar planets to the structure and evolution of galaxies. In this first lecture, I will motivate the critical need to understand the molecular interstellar medium over scales 0.1-100 pc as this impacts our descriptions of high-redshift submillimeter galaxies and the development of circumstellar disks from which planets emerge. From this need, I will summarize the most compelling questions to address with current and future facilities to augment our understanding of star formation. These questions provide the groundwork for the remaining three lectures. Finally, I will summarize and explain observational tools and methods available to astronomers to study the molecular interstellar medium with an emphasis on line emission within the millimeter and submillimeter bands.
Molecular clouds are the exclusive sites of star formation in galaxies. Therefore, a limiting step for star formation on galactic scales is the formation of giant molecular clouds from the diffuse atomic medium. I will first review the requirements necessary to develop significant abundances of molecules within the interstellar medium. Several large scale processes (Parker Instability, gravitational instability, magneto-rotationalinstability) that have been proposed to foster such conditions will be described. I will discuss the large scale distribution of molecules within galaxies and the Milky Way that provide observational constraints to the theories. Once molecules have formed, cooling line emission regulates the thermal state of the gas. I will review the heating and cooling processes within molecular clouds.
The evolution of a molecular cloud and the development of high density, gravitationally unstable cores that lead to newborn stars are strongly coupled to the prevailing cloud dynamics. I will review the virial theorem and the observations that have evaluated the equilibrium state of molecular clouds. I will provide a brief overview of turbulence and the observational tools that constrain the properties (velocity spectrum, driving scale) of turbulent flows in molecular clouds. The observational record of magnetic fields in molecular clouds and cloud cores will also be examined.
The competing theories of star formation and cloud evolution assign very different gas dynamics to the low density substrate of clouds and the role these dynamics play in the formation of protostellar cores. In one view, molecular clouds are supported against self-gravity by the interstellar magnetic field such that star formation is ultimately regulated by the rate of ambipolar diffusion that generates magnetically supercritical cores susceptible to gravitational collapse. In contrast, turbulent fragmentation poses that molecular clouds rapidly evolve due to super-Alfvenic turbulence. Star forming cores within the cloud result from the inevitable shocks that compress localized parcels of gas that decouple from the overlying turbulent flow. The expansion of HII regions and shells driven by supernova may also trigger the development of gravitationally unstable cores that leads to additional star formation. I will review these theories and describe future observations that can test these descriptions.
Gloria Dubner (Instituto de Astronomía y Física del Espacio, Ciudad Universitaria)
Supernova remnants (SNRs), the aftermath of violent stellar explosions, have a profound impact on the ecology of the host galaxies. They enrich the interstellar medium (ISM) with heavy elements and inject enormous amounts of energy, heating, stirring and irreversibly modifying the surrounding gas. Supernova remnants create shock waves in such extreme conditions that cannot be reproduced in terrestrial experiments, they accelerate particles to relativistic speeds, and can create the most compact objects in the Universe. Thus they are very valuable astrophysical laboratories to investigate the numerous physical processes involved in their evolution and interaction with the ISM. SNRs can emit radiation throughout the whole electromagnetic spectrum, from metric waves to gamma-rays. The lectures will focus on the characteristics,origin and evolution of the different kinds of SNRs, the relevant radiation proceses in the different spectral regimes, and the analysis of the information obtained from multifrequency observations.