This is page is a very brief introduction to what I study geared to the general public. If you are a professional astronomer you might be more interested in the publications page.
Stars are an important part of the Universe. They are especially important to us as they are the factories that produced us. When the Universe began it was mostly hydrogen, helium, and a little bit of lithium. Unfortunately this mix of atomic elements is not enough to make a human, a slug, or even water. The Universe needed a factory to create heavy elements before we could evolve. Stars provide that factory. Fusion, the process through which stars derive their energy, can create heavier elements if the star is large enough. Helium, Carbon, Oxygen, Silicon, and Iron. Unfortunately, that's still not a very diverse group of elements.
Under certain conditions a massive star will explode causing a supernova. This massively energetic process actually creates a slew of elements and ejects the Helium, Carbon, Oxygen, Silicon, and Iron from the core. These elements will float around in space and some will gravitationally collapse to form a stellar system. The chemistry of that new star system will be enriched with the elements produced in the supernova. That is why we have such a diverse assortment of atomic elements and chemistry on this planet, because stars that came before our Sun created them.
Stars are also the source of all of our power. Our Sun is responsible for fueling the growth of all the biomater which we now use as oil and coal, and Nuclear power is derived from elements produced by other stars. Even the hydrogen we collect right now is derived from natural gas mines. We know a lot about how stars evolve and die, but we know very little about how they form. That is what I am studying.
Stars form out of large clouds of molecular gas. We call these clouds dense molecular clouds, though on Earth a "dense molecular cloud" would be considered a vacuum. Molecular clouds typically have densities of about 100 to 100,000 molecules per square centimeter, which seems like a lot, until you realize that the density of the atmosphere at sea level is about 30,000,000,000,000,000,000 molecules per square centimeter. These molecular clouds look like dark patches in the sky at optical wavelengths (the light we detect with our eyes). An example of that is the cloud B68 (shown below, thanks to the European Southern Observatory). The reason these clouds appear dark is that the dust within the clouds absorbs the light from the stars behind the cloud.
In order to understand what is happening in these clouds I use millimeter and submillimeter radio telescopes. The molecules in these clouds produce emission at specific frequencies in these wavelength ranges which we see as spectral lines. They allow us to measure the chemical composition of the molecular clouds as well as determine their motions. There are several millimeter and submillimeter observatories in the United States. I usually travel to Western Massachusetts, Arizona, or Hawaii to observe these clouds. Below are pictures of the Green Bank Telescope in West Virginia, the Submillimeter Telescope in Arizona, and one antenna of the Submillimeter Array in Hawaii.
One benefit of looking at the molecular line emission from clouds is that motions within the clouds can be traced through the doppler shift they cause in those lines. Since I am interested in studying how giant molecular clouds form into comparably small stars I am most interested in studying collapse motions. Luckily these motions have a specific spectral signature called the blue-asymmetric infall signature. As a result of collapse a spherical cloud will have a broadened line profile caused by the blue-shifted signature of the back of the cloud as it approaches the observer and the red-shifted signature of the front of the cloud as it moves away from the observer. The line will also be self-absorbed because some of the radio waves emitted in the back of the cloud will be reabsorbed as they travel through the cloud. The motions in the cloud combined with the excitation conditions in a collapsing cloud to preferentially absorb the red-shifted emission, resulting in a blue-asymmetric spectral line. The figure below is an attempt to illustrate more clearly where parts of the spectral line come from. The circle represents a collapsing sphere, the eye to the left is an observer, and below the observer is the observed spectral line. Each part of the line is color coded to the part of the sphere in which the emission likely came from. The highest velocity blue-shifted and red-shifted gas (the bluest and redest regions in the figure) arise from a small region near the center of this cloud while the emission near the center of the line (maroon) arises from quite a large region in the cloud.
