Wednesday, February 10, 2010

Runaway Star

A hypervelocity star is a type of star which travels at a sufficiently high velocity with respect to its host galaxy’s rest frame that its velocity exceeds the galaxy’s local escape velocity. This places the star on a trajectory which removes it from its host galaxy. Gravitational interactions and supernova explosions in binary systems are two possible mechanisms that can produce hypervelocity stars. A paper by Andreas Irrgang, et al. (2010) entitled “The Nature of the Hyper-Runaway Candidate HIP 60350” explains the nature of one such hypervelocity star.

Kinematical observations of HIP 60350 show that it has a velocity which exceeds the local escape velocity of the Milky Way galaxy. This places HIP 60350 on a trajectory that will remove it from the Milky Way galaxy. Tracing its origin back to the plane of the Milky Way galaxy, the estimated travel time of HIP 60350 is about 14 million years. Given an estimated age of 45 million years for the star, a shorter travel time is consistent with the runaway nature of the star. So far, neither gravitational interaction nor a supernova explosion in a binary system can be strictly confirmed or rejected for HIP 60350.

In addition, a neutron star formed from an asymmetric supernova explosion can have sufficient ‘kick’ imparted to it for it to become a hypervelocity star. One such neutron star is RX J0822-4300 and it is measured to travel at a remarkable speed of over 1300 kilometres per second.