Cosmic Strings and The Origins of Globular Clusters

Abstract

Background: Globular clusters are galactic structures whose origin is not well understood. In this paper we propose that their origin may be found in the accretions formed around cosmic string loops.

Methods: To test this hypothesis we derived the mass distribution that would be associated with the ac- cretions and compared it to the observed mass distribution of globular clusters in our galaxy. Our derived distribution left us one free parameter (cosmic string tension) which we varied to optimize the fit. Once optimized, we compared the shape of the distribution and the number density that our model predicted with empirical observations. Later, we derived how velocity effects would alter the shape of this distribution.

Results: We achieved significant agreement between our model and observed values. Furthermore, the op- timal tension corresponds to particle physics theories that have not been ruled out. Our analysis further suggests that globular clusters form around slowly moving (< 3% the speed of light) cosmic string loops; any model with significantly faster cosmic string loops would contradict our hypothesis.

Limitations: Our results were obtained by using numerous approximations (such as the Zel’dovich approx- imation) and thus should be treated as an order of magnitude estimation. Our data was also limited to observed globular clusters within the Milky Way, limiting our sample size to approximately 120 globular clusters.

Conclusions: We managed to obtain strong agreement between our model and observed globular clusters, suggesting that they may be seeded by cosmic string loops. This also serves to explain many other charac- teristics of globular clusters, such as age, density and location. The analyses used in this report can also be used when considering the formation of other accretion objects, such as ultra-compact-minihalos.