The Galactic path of stellar black holes and neutron stars

Abstract

The kinematics of black hole and neutron star X-ray binaries in the Galaxy should help to know their birth place and constrain their evolution. We have used multiple tools of modern astronomy to determine the trajectories in the Galaxy and track the origins of black hole and neutron star X-ray binaries that are of topical interest in astrophysics. We find three distinct classes of black hole and neutron star X-ray binaries: (1) low mass X-ray binaries that move at high velocities on galactocentric orbits similar to the most ancient stars born in the Galactic bulge and the halo, (2) those that move in the Galactic disk along paths that resemble the circular orbits of massive stars formed in the disk, and (3) high and intermediate mass X-ray binaries running away from their parent regions of star formation. Here we discuss some of the cases studied. The large transverse motions of neutron stars (NS's) in the plane of the sky are believed to result from kicks imparted in natal supernova (SN) explosions. SN explosions are usually invoked in models of the core collapse of massive stars onto black holes (BH's), but until present there have been few observations that can constrain the models of the physical processes by which stellar-mass black holes are formed. The velocity in three dimensions and the galactocentric orbit can be used to gain insight into this issue, tracking the compact object back to its birth place and constraining the energy of any putative natal kick. Compact microquasar jets are ubiquitous among accreting black holes and neutron stars, and their motion in the plane of the sky can be followed with high precision by astrometry at radio wavelengths with Very Long Baseline Interferometry (VLBI). The proper motion can also be determined by astrometry of the donor star at optical wavelengths. Optical and IR spectroscopy of the companion star provides the line of sight velocity of the system. Knowing the distance either from VLBI or from the properties of the donor star, the Galactic orbit of the X-ray binary can be computed using a Galactic potential model. Here we summarize the results of a series of papers on individual objects, on which we search for some new constrains to the physical models that describe the formation of stellar-mass black holes and neutron stars.