A runaway star
is one which is moving through space with an abnormally high velocity
compared to other stars around it. The velocity is supersonic
relative to the surrounding interstellar medium
. The proper motion
of a runaway star often points exactly away from a stellar association
, whose member it therefore once must have been before it was hurled out.
Two possible mechanisms may give rise to a runaway star:
- In the first scenario, a close encounter between two binary systems may result in the disruption of both systems, with some of the stars being ejected at high velocities.
- In the second scenario, a supernova explosion in a multiple star system can result in the remaining components moving away at high speed.
While both mechanisms are theoretically possible, astronomers generally favour the supernova hypothesis as more likely in practice.
One example of a related set of runaway stars is the case of AE Aurigae
, 53 Arietis
and Mu Columbae
, all of which are moving away from each other at velocities of over 100 km/s (for comparison, the Sun
moves through the galaxy at about 20 km/s faster than the local average). Tracing their motions back, their paths intersect near to the Orion Nebula
about 2 million years ago. Barnard's Loop
is believed to be the remnant of the supernova that launched the other stars.
Another example is the X-ray object Vela X-1, where photodigital techniques reveal the presence of a typical supersonic bow shock hyperbola.
- Blaauw A., Morgan W.W. (1954), The Space Motions of AE Aurigae and mu Columbae with Respect to the Orion Nebula, Astrophysical Journal, v.119, p.625
- Hoogerwerf R., de Bruijne J.H.J., de Zeeuw P.T. (2000), The Origin of Runaway Stars, Astrophysical Journal, v. 544, p.L133