* Astronomy

Title: The Hypervelocity Star SDSS J090745.0+024507 is a Short-Period Variable
Authors: Cesar I. Fuentes, K. Z. Stanek, B. Scott Gaudi, Brian A. McLeod,
Slavko B. Bogdanov, Joel D. Hartman, Ryan C. Hickox, Matthew J. Holman

Researchers have taken high-precision photometry of the hypervelocity star SDSS J090745.0+024507 (HVS), which has a velocity of v=709 km/s, and is on course to leave our galaxy. It has likely been ejected from the supermassive black hole in the Galactic centre.

"It's the first clear-cut case of a star that's no longer gravitationally bound to the Milky Way" - Warren Brown, astrophysicist with the Harvard-Smithsonian Centre for Astrophysics.

The observations on the star were obtained on two nights using the 6.5m Multiple Mirror Telescope Observatory, and is supplemented by lower precision photometry obtained on four nights using the Fred Lawrence Whipple Observatory (FLWO) 1.2m telescope. The high-precision photometry indicates that the hypervelocity star is a short-period, low-amplitude variable, with period P=0.2-2 days and amplitude A = 2-10%. Together with the known effective temperature of about 10,500 K (spectral type B9), this variability implies that the hypervelocity star is a member of the class of slowly pulsating B-type main sequence stars, thus resolving the previously-reported two-fold degeneracy in the luminosity and distance of the star.
The star has a heliocentric distance of 71 kpc, and an age of about 0.35 billion years. The time of ejection from the centre of the Galaxy occurred less than 100 Million years ago,
and thus the existence of the star constitutes observational evidence of a population of young stars in the proximity of the central supermassive black hole about 0.1 billion years ago. It is possible that the star was a member of a binary that was tidally disrupted by the central black hole.



The star is currently 160,000 light years from the centre of the galaxy and still has to travel twice that distance before it leaves the Milky Way.
It is estimated that there is about 10,000 more super-fast stars in our galaxy and that tracking their progress could reveal information about the gravitational forces that hold the galaxy together.
At 709-kilometre-per-second the star is the swiftest ever spotted in the outskirts of our galaxy, travelling at twice the speed needed to escape from the Milky Way. Runaway stars have been seen before, but the previous record-holder was seen travelling at a mere 490 kilometres per second, and all of them are still confined in our Galaxy.

Read More (PDF , 80kb)