The fastest thing in our galaxy isn’t a comet, or a rogue planet, out of orbit. Rather, it is a runaway star cruising at an astonishing rate of 26-million miles per hour (43 million km/hr) on a path out of the Milky Way. Dubbed US 708, this star moves at such a fast pace that it can escape into intergalactic space by breaking free from the gravitational pull of the galaxy.
These types of stars aren’t that out of the ordinary. In fact, they are classified as hypervelocity stars (HVSs), which can move at an average rate of 2-million miles per hour, in comparison to the 450, 000 miles per hour movement of our own Sun. Unlike ordinary HVSs, however, this particular star is unique in that it moves at an exponentially faster rate. All previously detected hypervelocity stars were also similar to our Sun, in a sense that they were Main Sequence Stars. However, US 708 is what is known as a hot sub-dwarf, which are small, but have extremely high temperatures, and are predominantly made of helium, which is extremely combustible.
The runaway US 708 was first identified in 2005 and has been tracked by Stephan Geier and his colleagues for quite some time. Using archival data and current data, plus the observation of its movement over the past 70 years, they have been able to pinpoint the star’s travelling speed.
Scientists used to believe that HVSs originate from the monster black hole found in the dead center of our Milky Way, which can fling stars out of the galaxy due to its tremendous gravitational muscle. However, new research breaks this belief in the case of US 708.
US 708 might have orbited another neighboring star at a great speed with a small distance between them. It is suggested that the other star, identified as a white dwarf, exploded to its fiery death into a supernova and kicked the US 708 into motion on its rogue path. Combining the US 708’s already fast rotational speed with the sudden loss of a gravitational tether was enough to send it flying with colossal speed.