|
Q. Possible role for galaxy harassment in moving member objects away from LMC?
One mechanism that can remove stars and other objects from galaxies is a very suggestively named physical process called "galaxy harassment", which is defined as a process in which multiple high-speed encounters take place between galaxies. This process is particularly common in rich clusters of galaxies; I note that some clusters of galaxies end up with 5 or 10 percent of their stars being in between the member galaxies rather than inside the galaxies!!
I know little about the process of galaxy harrassment (and I really really hate to admit that I don't know something!).
So I offer this quotation from Penn State University's Astronomy 801 course materials, in an attempt to shed some light on this issue:
The relative velocity between galaxies plays a very important role in galaxy interactions. If two galaxies are moving too fast with respect to each other, the strength of the dynamical friction between them will not be large enough to slow them down and cause them to merge. The question is: Do these galaxies remain completely unchanged, or do they experience some changes as they have a “near miss” collision? Inside of galaxy clusters, spiral galaxies should experience multiple weak encounters as they pass by many of the other galaxies in the cluster with large relative velocities. Although we do not expect each of these weak encounters to produce dramatic tidal tails, bursts of star formation, and eventual mergers, the galaxies are not unaffected. Each minor encounter is likely to alter the shape of the spiral galaxy and to strip off some of its outer, weakly bound stars. This process is called Galaxy Harassment, and the effect that it has on the galaxies is also known as “tidal truncation” because the galaxies should slowly shrink as they lose more and more stars.
Remember that clusters like the Virgo cluster are known to contain a much higher percentage of elliptical galaxies than we find in poor groups. We think that the reason for this is that the spiral galaxies are altered by processes inside the cluster. It is likely that some combination of major mergers in the outskirts of the cluster and galaxy harassment in the inner regions causes the spirals to become elliptical galaxies. The Galaxy Harassment model also predicts that there should be a population of stars floating around inside of the cluster, unattached to any particular galaxy. Recently, astronomers have identified both red giant stars and planetary nebulae in the Virgo Cluster that are not associated with any one galaxy. These “intracluster stars” appear to be those predicted by the models of Galaxy Harassment.
|