Jorma Harju: Research

My research focusses on the inital stages of star formation taking place in dense cores of molecular clouds. My primary interests are in understanding the coupling between the dynamics and the chemical evolution of a contracting core, and in estimating the duration of the prestellar phase, i.e., the time between the formation of a gravitationally bound core and its collapse to form a protostar. I'm addressing these issues by determining the physical and chemical properties of dense cores through molecular line and dust continuum observations, and by comparing the core characteristics with theoretical models concerning their dynamical and chemical evolution.

In recent times, I have worked in close collaboration with scientists with the Centre for Astrochemical Studies, MPE, in particular Olli Sipilä and Paola Caselli. I visited the MPE during the first half of 2015. Other close collaborators are Mika Juvela (University of Helsinki) and Stephan Schlemmer (University of Cologne).
We have observed molecular filaments and cores at different stages of evolution and different environments using high performance instruments. The cold and obscured regions where new stars are born can be best studied at radio and infrared wavelengths. We have utilized single-dish radio telescopes and intereferometers like APEX, SOFIA, VLA, and ATCA, and we take a great interest in the ALMA project.

In order to interpret the data we are building models of prestellar cores where the physics and chemistry are described in a consistent manner. A chemical model program called pyRate has been developed mainly by Olli Sipilä. The physical models and chemical abundances are used as input for Monte Carlo radiative transfer programs developed by Mika Juvela. These programs produce simulated observations, e.g., molecular line and dust continuum maps, allowing direct comparison with data from currently available and future instruments.