Hyper-velocity stars
A star that is ejected at very high velocity (on the order of 1,000 km/s) from the center of a galaxy due to interaction with a massive central black hole. The existence of hypervelocity stars was first proposed in 1988. Computer models indicated that hypervelocity stars ought to be a natural consequence of binary stars coming close to the supermassive black hole known to exist at the heart of our own Milky Way Galaxy. When a binary swings too close to the central black hole, the intense gravity can tear the binary apart, capturing one star while violently flinging the other outward at enormous speed.
In 2005, the first hypervelocity star was discovered by astronomers using the Multiple Mirror Telescope in Arizona. Known as SDSS J090745.0+024507, it is 71 kiloparsecs from the Sun and moving through the outskirts of the galaxy – the so-called galactic halo – at about 850 km/s (528 miles/sec). This is more than twice the velocity needed to escape the Milky Way. SDSS J090745.0+024507 is expected to leave the galaxy altogether within 80 to 100 million years.
European groups subsequently identified two more hypervelocity stars, one of which may have originated in a neighboring galaxy, the Large Magellanic Cloud. In January 2006, the discovery of two more such objects was announced by the Arizona group, bringing the total number of known stellar exiles to five.
The two most recently discovered hypervelocity stars are both short-lived types, about four times more massive than the Sun. One lies in the direction of the constellation Ursa Major and is designated SDSS J091301.0+305120. It is traveling out of the galaxy at a speed of about 556 km/s (1.25 million mph) and is currently located about 240,000 light-years from us. The other, in the direction of the constellation Cancer, is designated SDSS J091759.5+672238. It is moving outward at 639 km/s (1.43 million mph) and is presently about 180,000 light-years away.
Astronomers estimate that a star is thrown from the galactic center every 100,000 years on average and that altogether there are about 1,000 hypervelocity stars heading out of the Galaxy. Finding them, however, among a stellar population that exceeds 100 billion is not easy.
Hypervelocity stars are becoming important tools for understanding massive black holes and also offer a unique probe of galactic structure. During their lifetime, these stars travel across most of the Galaxy. By measuring their movements across the sky, it ought to possible to refine our knowledge of the shape of the Milky Way and about the way its dark matter is distributed.
Hello everyone and thank you for reading this OOTD. The information posted here comes from this site and
here's the link to it.
We on Galaxy Zoo are very lucky, we have nine of the 10 hyper-velocity stars on the SDSS footprint. And here they are. Only three say they are HVS.Thank you dear Tommy for getting the objID's for the HVS's and for remembering the HVS stars I posted a while ago on your newbies' thread.
Thank you dear Alice for beautifying the OOTD.
Thank you dear Jules for the links and for saving this OOTD at the last minute like a hero out of a book. 
HVS 1
SDSS J090744.99+024506.8 -- Variable Star
588010358530507060
Believe it or not I found another one five minutes after I posted this.
http://cas.sdss.org/astro/en/tools/explore/obj.asp?id=587732135914635282
HVS 2
SDSS J093320.86+441705.4 -- White Dwarf
588013383268565133
Number 3 not in SDSS
Number 4
[BGK2006] J091301.01+305119.8 -- Star
588017979949842518
Number 5
SDSS J091759.47+672238.3 -- Star
587738068348960770
Number 6
SDSS J110557.45+093439.4 -- Star
587732771585458263
Number 7
[BGK2006] J113312.12+010824.9 -- White Dwarf
588848901520359456
Number 8
[BGK2006] J094214.04+200322.1 -- Star
587741821063790648
Number 9
[AG92] 16400 -- Horizontal Branch Star and [BGK2006] J102137.08-005234.8 -- Star
588848898828140657
Number 10
[BGK2006] J120337.86+180250.3 and LSPM J1203+1802 -- High proper-motion Star
587742775095918754
I would like to say Happy Birthday to my husband Benito, today is his birthday. Thank you dearest for your love and support ever since we met.And a special hello to all my sisters from the Apostolado School.
And my children, Laura, Benny and Moti and grandkids. 
