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X-ray binaries are binary systems containing a compact object (neutron star or a black hole) accreting matter from a companion star (typically a star like the Sun). Over time, the strong gravity of the compact object pulls matter from the surface of the donor star and strips its outer layers. Theoretical models predict that as the material falls towards the neutron star/black hole, it loses angular momentum and energy through emission (mostly in X-rays). The stars in the binary get closer as their orbital period shrinks. These predictions have made measurement of orbital period and its changes over time in X-ray binaries a direct method to test our understanding of how black holes and neutron stars devour other stars.

Classically, it was thought that any observable change of orbit in X-ray binaries would require observations over centuries/millennia to be detected. However, over the past three decades, changes in orbital period have been observed in in a handful of eclipsing X-ray binaries over timescale of ~years. These findings suggest that there are more complex physical mechanisms (like the star’s magnetic field) significantly impacting evolution of X-ray binaries. Thus a careful study of orbital changes in a larger sample of sample of X-ray binaries is needed to better understand evolution in these systems.

In this project, the student will analyze recently obtained X-ray data with the Swift satellite of a well-known eclipsing X-ray binary, for which the orbital period waslast measured in the year 2000. This will allow a direct estimate of the rate at which the orbital period has changed in this system and thus constrain the evolution of this system. We anticipate that the X-ray analysis will be included in a refereed publication, with the student as a co-author, pending satisfactory completion of the project.



Dr Richard Plotkin

Senior Research Fellow - Peter Curran Memorial Fellow (Formerly)

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