Evolution of Circumstellar Disks Surrounding Massive Stars

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Different types of disk-like distributions of gas, stars, and planets are found in the Universe. Our Sun is in a spiral arm within a disk-like distribution of stars, gas, and dust in our Galaxy. The Earth formed in a disk of material surrounding the Sun. Black holes have disks of material swirling about them, and there are many more examples of the ubiquity of such disks. Consequently, knowing how disks form and appreciating the processes operating in them are critical to understanding many objects in astrophysics. My research focuses on massive stars, in particular B-emission stars (Be stars), which are surrounded by gaseous disks. A variety of techniques are used to observe these remarkably bright objects, hundreds of which exist right in our Galaxy. Providing an ideal environment for studying disks, these stars can spew out one thousand times more energy per second than our Sun, and as a result they go through different stages in their lifetime more quickly. Since the disk is formed from gas launched from the star or gas from a binary companion, it is not shrouded in dust like disks in star forming regions, allowing for easier observing. The rotation rate of the star is also quite fast causing the materials inside the star to mix, affecting the star's production of energy and its lifespan. When a Be star reaches the end of its life and blows up as a supernova, it can trigger a new generation of stars, directly affecting the evolution of its surroundings. Despite decades of study, the fundamental question to be addressed in this field is why the disk forms and my research will tackle this important puzzle. I build computer models and use real observations to constrain my work. Rapid stellar rotation seems to be an essential ingredient, but something else must help to eject the material - perhaps, a pulsation on the stellar surface, a push from the radiation field or maybe the material is donated by a nearby companion. My research will allow these complex details to be sorted out. The star is the energy source for the disk. Starlight is scattered, reabsorbed, and polarized by the disk before we collect it with various techniques. Therefore, collected light has signatures from the star and disk, which gives lots of information. Distinct wavelengths of light come from different parts of the disk system where temperature and other conditions may be quite different. As such, my research will investigate the entire range of light (wavelengths) to understand all the different parts of the star/disk system. There is a long history of pioneering discipline-specific study and expertise in Canada, especially at Western University, of Be star disks. The results of my program will not only provide key results for understanding this type of disk but will help researchers worldwide apply the insight to better understand other types of disks, placing important constraints on the formation of massive stars and on the evolution of stars and galaxies.