Astronomers detect star leaving the Milky Way at record speeds

An international team led by astronomers from Queen's University Belfast has identified the fastest ever star on an escape trajectory from the Milky Way – the white dwarf US708, which is traveling at a staggering 1,200 km per sec (746 miles per sec). The discovery of this star may shed light on the astronomical events that are vital to the calculation of distances in our universe.

The team used data gathered by the Pan-STARRS1 telescope located on Mount Haleakala, Maui, over the past 59 years to determine the runaway star's speed and direction. From this it was concluded that US708 originally belonged to a binary star system, whence it was paired with another enormous white dwarf.

It is believed that binary systems of this kind often result in a thermonuclear explosion known as a 'Type la' supernova. This particular form of star death occurs when the incredibly dense larger white dwarf feeds on the stellar material of its partner (in this case the smaller white dwarf US708) until it reaches critical mass – the equivalent of 1.4 solar masses. This is known as the Chandrasekhar limit, and very soon after the star explodes in spectacular thermonuclear fashion.

It is hoped that further examination of US708 may shed light on the phenomenon that shunted the star into its escape trajectory, as this Type la supernova is a vital astronomical marker used by scientists to determine the distances of far off galaxies.

Astronomers are able to use these distinctive supernovae as distance markers because they always throw off an identical amount of light. Scientists can then observe dimming in the known luminosity of this brilliant light source, and apply the inverse square law in order to ascertain how far away the supernova is, and also the galaxy to which it belongs.

"Several types of stars have been suspected of causing the explosion of a white dwarf as supernova of type Ia. Until now, none of them could be confirmed," says Stephan Geier, fellow of the European Southern Observatory and leader of the study. "Now we have found a delinquent on the run bearing traces from the crime scene."