We report the discovery of 30 stars with extreme space velocities ( \gtrsim 480 \mathrm { km s } ^ { -1 } ) in the Gaia -DR2 archive .
These stars are a subset of 1743 stars with high-precision parallax , large tangential velocity ( v _ { tan } > 300 \mathrm { km s } ^ { -1 } ) , and measured line-of-sight velocity in DR2 .
By tracing the orbits of the stars back in time , we find at least one of them is consistent with having been ejected by the supermassive black hole at the Galactic Center .
Another star has an orbit that passed near the Large Magellanic Cloud ( LMC ) about 200 Myr ago .
Unlike previously discovered blue hypervelocity stars , our sample is metal-poor ( -1.5 < [ Fe/H ] < -1.0 ) and quite old ( > 1 \mathrm { Gyr } ) .
We discuss possible mechanisms for accelerating old stars to such extreme velocities .
The high observed space density of this population , relative to potential acceleration mechanisms , implies that these stars are probably bound to the Milky Way ( MW ) .
If they are bound , the discovery of this population would require a local escape speed of around \sim 600 \mathrm { km s } ^ { -1 } and consequently imply a virial mass of M _ { 200 } \sim 1.4 \times 10 ^ { 12 } M _ { \odot } for the MW .