On the Origin of Hypervelocity Stars

University essay from Lunds universitet/Astronomi - Genomgår omorganisation

Author: Karl Wahlberg Jansson; [2010]

Keywords: Physics and Astronomy;

Abstract: Hypervelocity stars (HVSs) are stars located in the Galactic halo travelling with extremely high speeds. They are produced when a binary approches the supermassive black hole (SMBH) in the Galactic Center (GC) and gets tidally broken up. In this process one of the stars is ejected with high velocity. The angle between the velocity of the incoming binary and the velocity of the ejected HVS is almost 180◦. Lu et al. (2010) claims that all the HVSs come from two distinctive existing disks of stars by stating that the planar structure of the stars is preserved since the deflection angle is 180◦. I derive different properties of HVSs, e.g. the deflection angle and the break-up radii as functions of the SMBH mass, the initial velocity of the binary, the ejection velocity, the closest approach of the binary, the binary separation, the stellar radii and the stellar masses. I also discuss what happens to the other star in the binary and the future of the HVSs. I test the results of Lu et al. (2010) by trying to find combinations of two planes that have a better fit than their results. I also use a larger sample of stars than they do and also I consider the effects of the Galactic potential on the trajectories of the HVSs. My conclusions are that there exist many more combinations of two planes that fit the origin of the HVSs better than the two existing disks so it is not really possible to claim that the HVSs come from these two disks. In the final section I discuss what happens if you change some parameters, the SMBH mass and the binary separation, and also how you could extend the project in the future, e.g. if you add post-Newtonian effects and if there is an assymmetric dark matter halo in the Milky Way.

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