Undergraduate research projects

Protostellar disks

The story begins with a giant molecular cloud that has fragmented. The fragments collapse under the force of gravity. Since they have some spin, they tend to form into flattened disks. In the very early stages, it is believed that very little material goes into the center of the disk, where the star will eventually form. Most of the material forms a large torus, which is the disk surrounding the central protostar. Waves form in the disk, driven by shear forces and gravitation. Instabilities grow, which tend to transfer matter and angular momentum inward onto the central star. Much of our research involves studying how the geometry of the system affects the mass and angular momentum transport in these disks. Future interest: radiative cooling, modeling spatially resolved stars, vortex instabilities.

Magnetohydrodynamic Shocks

Hydrodynamic (HD) shocks are formed when supersonic fluid meets subsonic fluid. When the flow is entirely subsonic, waves can propagate upstream. This allows the signal of any barriers to be sent back through the fluid, which can then more easily flow around the object. When the flow is supersonic, sound waves cannot propagate back upstream to “warn” the fluid of the upcoming barrier. A shock wave arises when the fluid runs into the subsonic barrier.

Magnetodhydrodynamic (MHD) shocks arise when the fluid is plasma, where there is separation between the positive and negative charges. This can give rise to magnetic fields, which allow for more kinds of waves to propagate through the fluid. There are two kinds of magnetosonic pressure waves, fast and slow waves. The slow waves travel slower than sound speed, and the fast waves travel faster than the sound speed. The fast MHD waves make modeling of plasma shocks difficult, since they can carry information back upstream even when the flow is supersonic. There are also Alfven waves, which are oscillations along the magnetic field lines. They oscillate tangentially, like waves along a plucked string. Future interest: Include radiative cooling in the modeling.

Strange quark stars

Neutron stars are the leftover cores of massive stars that have gone through the supernova phase. The outer part of the star is blown off in a gigantic explosion, leaving a very dense, very hot core made of mostly neutrons. Another possibility is that the dense material may break down even farther, into a quark plasma. Modeling neutron stars and strange quark stars may give rise to signatures that would allow us to tell the difference between them. Future interest: More sophisticated models involving general relativistic modeling and adaptive mesh code.