We present the serendipitous discovery of the fastest Main Sequence hyper-velocity star ( HVS ) by the Southern Stellar Stream Spectroscopic Survey ( S ^ { 5 } ) .
The star S5-HVS1 is a \sim 2.35 M _ { \odot } A-type star located at a distance of \sim 9 kpc from the Sun and has a heliocentric radial velocity of 1017 \pm 2.7 \mathrm { km s ^ { -1 } } without any signature of velocity variability .
The current 3-D velocity of the star in the Galactic frame is 1755 \pm 50 \mathrm { km s ^ { -1 } } .
When integrated backwards in time , the orbit of the star points unambiguously to the Galactic Centre , implying that S5-HVS1 was kicked away from Sgr A* with a velocity of \sim 1800 \mathrm { km s ^ { -1 } } and travelled for 4.8 Myr to its current location .
This is so far the only HVS confidently associated with the Galactic Centre .
S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy , such as the Solar motion V _ { y, \odot } = 246.1 \pm 5.3 \mathrm { km s ^ { -1 } } or position R _ { 0 } = 8.12 \pm 0.23 kpc .
The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disk of young stars at the Galactic centre , and thus may be linked to its formation .
With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre , we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time .