Interstellar medium and protostars
Knowledge of the chemical and physical composition of the interstellar medium, its evolution, and the path that leads to the formation of a star is one of the main problems in modern astrophysics. Linked to this knowledge is the understanding of planet formation and the physics that regulates the galaxies and their evolution.
Significant progress in this area has been possible only relatively recently, relative to other areas of stellar astrophysics, thanks to the enormous technological developments in infrared, millimetre and sub-millimetre instrumentation, which are the spectral bands where regions of star formation are best traced. We mention here international facilities such as NASA's Spitzer space telescope, ESO's Very Large Telescope Interferometer – VLTI - for millimetre and infrared interferometry and the Hubble Space Telescope - HST - for high resolution optical and ultraviolet observations.
Thanks to Italian expertise in these areas, our researchers have significant success in observing time requests through Large Programs and in the development of new instruments such as the Atacama Large Millimeter/sub-millimetre Array - ALMA - that will be completed in 2012, but already operational in 2011, and the Herschel Space Observatory, the first space telescope to cover the entire wavelength range from the far-infrared to the sub-millimetre. For studies of the first phases of star formation, low, medium and high resolution spectroscopic observations in the optical and infrared with VLT instrumentation are also having a particular impact.
As far as the interstellar medium is concerned, enormous progress has been made recently in the understanding of the chemistry within molecular clouds on various spatial scales, that is, from diffuse clouds to pre-stellar cores and circum-stellar disks. These studies have been taken forward by ever-more complex chemical models, associated with observations of various molecular species using instrumentation, both from the ground and space-based, in the infrared to radio spectral regions.
Observations of the the regions in which star formation occurs are much more difficult. The only tracer of protostars turns out to be the low energy radiation emitted by the cold dust and molecules in these regions; this observational limit makes it difficult, for now, to place constraints on theoretical models.
Most of our knowledge of the star formation process is limited to stars of solar mass and below. However, it is stars more massive than 8 solar masses that dominate the energy release of galaxies and the chemical evolution of the Universe. To make progress in this field a large systematic investigation of our galaxy is underway. Here also, the various theories proposed are having difficulty in being confirmed with appropriate observational data.
As far as the observational study of the global properties of the interstellar medium and star formation is concerned, the aim is to use the dust emission at various wavelengths as a tracer of the physical conditions in all the phases of star formation.
There are also many programs underway involving the study of protostars and protostellar cores of both low and high mass, aimed at characterising sources in the very early phases of their formation. Other studies are focused instead on material and radiation jets from protostars, and their impact on the surrounding interstellar medium.
Alongside observational studies both theoretical and laboratory work are developed, in particular for dust in the interstellar medium and proto-stellar cores. In fact, most of our knowledge of the chemical and physical properties of dust and molecules in the interstellar medium is based on the comparison between observations and laboratory experiments, carried out, normally, at low temperatures. Theoretical studies that predict the spectra of macromolecules and nano-particles based on carbon, are also of particular importance.
The numerical codes developed for these theoretical studies use a wide range of national and international computing resources, providing a significant impetus to technological developments in computing, and, from the essentially astrophysical perspective, producing databases of great importance to the international scientific community. These data provide a useful guide for the planning and interpretation of new experiments and a precious resource for the interpretation of observations from future space missions.