Measuring the Shape and Orientation of the Galactic Dark-Matter Halo using Hypervelocity Stars

Details Measuring the Shape and Orientation of the Galactic Dark-Matter Halo using Hypervelocity Stars Measuring the Shape and Orientation of the Galactic Dark-Matter Halo using Hypervelocity Stars

Jul 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008hst..prop11782g&link_type=abstract

HST Proposal ID #11782. Cycle 17

Astronomy and Astrophysics

Astronomy

Scientific paper

We propose to obtain high-resolution images of five hypervelocity stars in the Galactic halo in order to establish the first-epoch astrometric frame for them, as a part of a long-term program to measure precise proper motions. The origin of these recently discovered stars, all with positive radial velocities above 540 km/s, is consistent only with being ejected from the deep potential well of the massive black hole at the Galactic center. The deviations of their space motions from purely radial trajectories probe the departures from spherical symmetry of the Galactic potential, mainly due to the triaxiality of the dark-matter halo. Reconstructing the full three-dimensional space motion of the hypervelocity stars, through astrometric proper motions, provides a unique opportunity to measure the shape and orientation of the dark halo. The hypervelocity stars allow measurement of the potential up to 75 kpc from the center, independently of and at larger distances than are afforded by tidal streams of satellite galaxies such as the Sagittarius dSph galaxy. HVS3 may be associated with the LMC, rather then the Galactic center, and would therefore present a case for a supermassive black hole at the center of the LMC. We request one orbit with ACS/WFC for each of the five hypervelocity stars to establish their current positions relative to background galaxies. We will request a repeated observation of these stars in Cycle 17, which will conclusively measure the astrometric proper motions.;

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