Allison Jo Mercer

Luminous Blue Variables

Allison Jo Mercer is currently working on a multi-wavelength astronomy project studying features surrounding volcano-like erupting stars. Called "Luminous Blue Variable stars" (LBVs), they can be highly unstable, sometimes ejecting as much mass as is contained in our whole solar system! Mercer has combined different radio frequencies to look at the mass that has ejected from the surface of these stars.

To the right is the controversial LBV source known as LBV 1806-20. The star that's embedded in the brightest spot at the lower right corner was once thought to be over 250 times the size of the sun! With recent data, the size of the star is thought to be closer to 36 times bigger than the sun...still nothing to sneeze at! The lower right corner of the image is actually the massive stellar wind of the star (the star itself is deeply embedded and not seen in this image). Utimately, LBV 1806-20 will blow up in an enormous cosmic explosion called a supernova. This is one of the sources Mercer is studying as part of her master's thesis work with Assistant Professor Cornelia C. Lang.

Ultra-Compact HII Regions

HII Regions are the compact regions of hot, ionized gas that surround young, massive stars. As part of an on-going project at Agnes Scott College under Professor Christopher De Pree, over a decade of observations were compiled and analyzed to provide a more robust classification scheme for HII regions in general. To describe the fundamental processes implied by the trends in the sources observed, Mercer worked with Professor John Blondin at NCSU to implement a Hydrodynamic (HD) code (VH-1) to simulate the evolution of these star-forming regions.

Shown to the left is a simulation of a massive O6 star in the presence of a circumstellar disk. Initially, the HII region exhibits a bipolar structure, which expands into a shell structure as the disk is blown away by the star.

Ultra-Luminous X-ray Source

Another project Mercer has worked on while at the University of Iowa is the radio emission from an Ultra-Luminous X-ray Source (ULX). This ULX is of particular interest because it is a possible intermediate-mass black hole. There are two common types of black holes: (1) black holes formed in the centers of supernovae that are a few times bigger than our sun, and (2) supermassive black holes that are at the centers of galaxies that are a few MILLION times the mass of our sun. This source is of particular interest because it's too bright to be a uniformly emitting, run-of-the-mill black hole, and too dim to be a supermassive black hole. There are a few possible sources of such bright X-ray emission, one of which is beamed emission from a smaller black hole, and another is an intermediate-mass black hole...a rare object indeed!

To the upper right is the optical image of NGC 5408, the galaxy that hosts the ULX source. The ULX source is located near the pink, butterfly-shaped star-forming region. To the lower right is the radio contour image of the ULX (marked with a cross) and the same star-forming region (Lang et al. 2007). Mercer worked on this project with Assistant Professor Cornelia C. Lang, and Associate Professor Phil Kaaret.