Article Summary #6

SDSS J013655.91+242546.0 - an A-type hyper-velocity star from the outskirts of the Galaxy

Tillich, A.; Przybilla, N.; Scholz, R.-D.; Heber, U. 2009, Astronomy and Astrophysics, Volume 507, Issue 2, 2009, pp.L37-L40 (A&A Homepage)
http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0910.5174

This paper presents an example of a study done on a hyper-velocity star in order to find its point of origin. Hyper-velocity stars are stars that become unbound to the galaxy due to their very high velocities, and sometimes they even escape their host galaxy.

Tilich et al. 2009 explain how the dynamical ejection by a suppermassive black hole can explain how these stars end up having such high velocities. In order to do that, finding the origin of the star and what mechanism explains its ejection is essential.

The first hyper-velocity stars were discovered in 2005 with radial velocity measurements. At this point, there are different opinions that scientists have about the point of origin if these unique stars: some think they form in the Galactic center, while others think that they are born in any area of the galaxy, not necessarily in the center, and their high speeds can be explained as being a cause of the tidal distribution of a dwarf galaxy in the galactic potential.

Since there are no measurements for proper motion, accurate trajectories for this kind of objects have not been found. The closest measurement achieved so far is only that of a high-velocity star (in contrast to a hyper-velocity star), a B-type star for which the trajectory was measured with known proper motions, radial velocity and spectroscopic distance.

That was the first fast star that was found that the star originated in the outer-rim of the galaxy, which proves that such a mechanism is possible. Tilich et al. 2009 managed to find the first hyper-velocity star that did not originate at the center of the galaxy, but also at the rim, and that is an A-type hyper-velocity star and its speed is ~590km/s.