13 Possible Hypervelocity Stars Identified in our Galaxy

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Posted on August 19, 2013

The first hypervelocity stars (HVS) have been discovered by scientists from Harvard-Smithsonian Center For Astrophysics almost a decade ago, in 2005. Since then many astronomers pursue the search for new HVS with aim to use the parameters of these stars to create new astrophysical models capable of explaining the behavior of supermassive black holes, particularly those which are located at the centers of galaxies, and the origins of HVS.

Researchers believe that hypervelocity stars originate from so-called three-body interactions between binary stars and supermassive black hole at the center of the galaxy. In essence, during such interaction one star from the binary system becomes bound to black hole, while its movement energy is transferred to the second member of the two-star system, and due to this transfer it literally gets “thrown” out of the galaxy. Term ‘hypervelocity’ means, that these celestial bodies exceed the regular stellar velocity limits: the typical speed of movement of HVS can reach 3-4 million kilometers per hour (approximately 1000km per second and above), while velocities of regular stars are at least ten times lower.

Research team including scientists from United States and Spain performed analysis of data obtained via Sloan Extension for Galactic Understanding and Exploration (SEGUE), project aimed to create a detailed 3D map of Milky Way galaxy. They were able to identify 13 new candidate hypervelocity stars, potentially exceeding the minimum escape speed from the galaxy with at least 90% probability (see a short definition of galaxy escape speed in video below). The paper detailing their research has been published at arXiv.org.

Authors of the study currently are not 100% sure that the stars they identified are really the hypervelocity stars. The speed of those objects reaching 700-1000km/s suggests that the supermassive black hole is the cause for such phenomena, when the star is ejected from the galaxy, since a massive gravitational force is required to rip the binary star system apart.

Interestingly, analysis of newly-detected HVS trajectories indicated, that they did not originate from the center of the Galaxy, so other ejection mechanisms (besides the impact of supermassive black hole) may be possible. Also, it can mean, that other neighbor galaxies may be the source of wandering hypervelocity stars which entered our galaxy at some distant moment in the past. According to calculations of scientists, one of HVS candidates could have escaped from Andromeda galaxy approximately one billion years ago.

Scientists admit, that extragalactic sources such as globular clusters, galactic tidal waves or satellite galaxies could be the sources of other identified HVS candidates. Further research on these hypervelocity stars could provide more information about the origin and composition of HVS, as well as give new insights into mechanisms of galaxy-scale gravitational forces.

Story by Alius Noreika, Source: Technology.org

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