Analyzing the observations made using NASA’s Spitzer WISE space telescopes, many runaway stars were discovered. Those stars are called that way for the remarkable speed they’re moving at in space. One way to identify a potential runaway star is to seek what in jargon is called “bow shock” and indicates the area between a magnetosphere and a surrounding environment. It’s an arc-shaped structure that extends in front of the star and can be very extensive.
The most famous runaway star is Zeta Ophiuchi, which moves through space at supersonic speed and has an incredibly spectacular bow shock. The astronomer William Chick from the University of Wyoming in Laramie led the team that looked for other similar stars in the archives of data gathered using the Spitzer and WISE (Wide-Field Infrared Survey Explorer) space telescopes. Chick himself presented the results of this research at the meeting of the American Astronomical Society in Kissimmee, Florida.
The materials that form the bow shock get heated and for this reason emit light, which shines in particular at infrared frequencies. William Chick and his colleagues examined the observations made at those frequencies, reproduced in red in the processed photographs, and found more than 200 images of arcs. At that point, they used the Wyoming Infrared Observatory, near Laramie, to verify 80 candidates and identify the sources that create the bow shocks.
In most cases the sources are massive stars, just like Zeta Ophiuchi. Their origin could be similar as well meaning that probably those runaway stars have received a boost from other stars that exploded in supernovae. Another possible mechanism that could propel a star at very high speeds is a supermassive black hole flyby that would determine a gravity assist effect.
According to William Chick not all the stars accompanied by a bow shock are runaway stars but there could be exceptions: in some cases, the bow shock could be for example a kind of shell remained from the cloud of gas and dust in which a newborn star was generated.
An almost opposite approach was chosen by another team of researchers led by Cintia Peri of the Argentine Institute of Radio Astronomy. They also used data collected by the Spitzer and WISE space telescopes but looked for stars known for their rapid movements. The observations of these stars were examined in search for a bow shock.
This type of research is far from new as some of the first bow shocks generated by runaway stars were discovered in the ’80s using the IRAS (Infrared Astronomical Satellite) satellite, one of the first space telescopes. However, Cintia Peri pointed out that the data collected by Spitzer and WISE have a much higher resolution. The consequence is that in cases of bow shock already known these data provide new details.
Research such as those ones are helping to reconstruct the history of massive stars by providing more information about their origin and evolution. Therefore those are spectacular cases but also interesting sources of scientific information on those stars’ lives.
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