Research

Planet Formation around Brown Dwarfs

Within just the past two decades, astronomers have discovered thousands of planets orbiting around other stars in our galaxy.  As more of these “exoplanets” are discovered, the search for extraterrestrial life becomes more exciting.  In order to understand how life might arise on these distant worlds, it is crucial to understand how the planets themselves may have formed.  One approach to answer this question is studying protoplanetary disks: clouds of gas and dust surrounding young stellar or sub-stellar objects.  Planets are thought to form from the material in these disks, but the exact mechanism is not yet well understood.

In order to characterize these protoplanetary disks, our group uses models to explain observed data.  We can vary the inputs to the model, which correspond to different physical characteristics of the disk; once the model fits the observations well, we can infer that the inputs of that model describe the properties of the disk.  These properties include mass, composition, and size, among others.  Based on these parameters, we can better constrain the conditions necessary for planets to form.

In particular, I study protoplanetary disks around brown dwarfs.  These objects are cooler and less massive than typical stars; yet despite their small size, they have been observed to have protoplanetary disks (Comerón et al. 1998) and even planet-sized companions (Gauza et al. 2015).  The formation mechanism(s) of brown dwarfs themselves are not well understood, much less their planetary companions.  I combine our group’s disk models with radio-wavelength ALMA observations to constrain both brown dwarf formation and the formation of their companions.  In my recent paper (Rilinger et al. 2019) I present disk masses and radii for two brown dwarfs in the Taurus Molecular Cloud.

ALMA observations (left), our models (center) and residuals (right) for two brown dwarfs in the Taurus Molecular Cloud: CFHT Tau 4 (upper) and 2M0444 (lower). These models allow us to constrain the radii of these disks, which in turn informs theories of brown dwarf formation.

ALMA observations (left), our models (center) and residuals (right) for two brown dwarfs in the Taurus Molecular Cloud: CFHT Tau 4 (upper) and 2M0444 (lower). These models allow us to constrain the radii of these disks, which in turn inform theories of brown dwarf formation.  From Rilinger et al. 2019. Click image to enlarge.