by Dan Gifford | Mar 23, 2012 | Daily Paper Summaries
Title: The XMM Cluster Survey: The Stellar Mass Assembly of Fossil GalaxiesFirst Author: Craig D. HarrisonFirst Author Institution: University of MichiganHow do you describe a fossil? Old? Imprinted? Dead? Pristine? A link to the past? As it turns out, the word fossil has been used to describe a distinct population of galaxies and systems of galaxies in our universe. Hierarchical structure formation models indicate that small things build larger things over cosmic time. When groups and clusters of galaxies form, dynamical friction causes the galaxies to lose momentum and kinetic energy, which can ultimately lead galaxies to merge. This dynamical friction has the greatest effect in high density regions, which causes mergers to create a large brightest cluster galaxy (BCG) at the center of these systems. Observations have identified a population of clusters that have a very large BCG, but not very many bright companions (ie, a magnitude gap exists) and called these Fossil Galaxies in Fossil Systems. The use of word fossil here is perfect because the BCG appears to live in a “dead” or depleted environment, and the entire merger history should be imprinted in its stellar population.So what can we learn from these fossil systems? Because of small samples, much of what we already know has come from simulations. These simulations indicate that fossil systems gain a large fraction of their mass at high redshift and earlier than non-fossil groups. One hypothesis is that growth of fossils was dominated early by in-fall of massive satellites which boosted the size of the fossil galaxy relative to its cousins in non-fossil systems, which evolved slightly more passively. Another...
by Katherine Rosenfeld | May 13, 2011 | Daily Paper Summaries
Einstein’s theory of General Relativity predicts all manner of strange astrophysical behaviors. Can we hope to observe these effects from supermassive black holes?
by Susanna Kohler | Mar 25, 2011 | Daily Paper Summaries
The closest known isolated radio pulsar also has one of the slowest rotation rates — far below what should be observable for a pulsar. This paper discusses X-ray and optical observations of this puzzling object.
