The BHBinary/Galaxy Evolution SurveyThis page is dedicated to a large program on the Very Long Baseline Array (BS237/BS280) that aims to discover the state of evolution of the black holes that should be resident in six major galaxy mergers in the nearby Universe, selected based on analysis by Carpineti et al. (2012). Click any galaxy below to see their information and notes on VLBA data products collected so far.
Almost all massive galaxies in the nearby Universe contain a supermassive black hole
(SMBH). In the chaotic aftermath of a galaxy collision , these two massive gravitational
bodies evolve gradually through drag on gas and stars to the center of the merging
system, and form a binary black hole there.
However, what is not known is what happens after that binary forms. We believe though circumstantial evidence that the pair will collide, however studies in numerical relativity have had trouble understanding how to take enough energy away from such a massive binary system to get it to in-spiral and eventually coalesce. If these systems can in-spiral in a sufficiently brief amount of time, they may be some of the brightest sources of gravitational waves in the Universe.
You'll notice all the galaxies above have a common feature: they all have what looks like a single core in the center, and otherwise seem to show some chaotic features. These were, in fact, key to our selection of these galaxies. We want to explore late-evolution merger dynamics; we know these galaxies appear to have undergone a semi-recent merger (they all show tidal features, hence probably merged within the last billion years), however enough time has elapsed since that merger so that the core of the merging system has settled down to have a relatively smooth potential well. That is, enough time has elapsed so that we estimate that the binary SMBH system should already be in an advanced stage of merger, or perhaps if in-spiral evolution is highly efficient, the systems may have already coalesced.
The task of this search is to image the cores of these "spheroidal post-merger galaxies" to resolve potentially one or two compact objects, representing one or two black holes residing at the center of these galaxies. The VLBA is ideal because it can reach extremely small (milli-arcsecond) resolution, to then map out any radio jet emissions arising from the black holes in these cores. Because we selected these galaxies because they were known to have radio emission, our specific task is to map this emission to determine whether it reveals a single or double black hole source, and determine the dynamics of the single or double black hole to then reveal a full view of the timescale over which these black hole monsters can coalesce.
Caitlin Witt (WVU Grad student)
Greg Walsh (WVU Grad student)
Julie Comerford (UC Boulder)
Our WVU undergrad team:
Rodney Elliott, Kris Wolfe, Kara Green, Simon Wirth