Kappa Cas: Runaway star plows a bow shock in the sky.

Gorgeous and Shocking: Bow Wave of a Runaway Star

Gorgeous and Shocking: Bow Wave of a Runaway Star

Bad Astronomy
The entire universe in blog form
Feb. 27 2014 7:45 AM

A Monster Star Plows Through the Galaxy? Shocking.

Kappa Cas

Photo by NASA/JPL-Caltech

Correction, March 6, 2014: Well, this will take a moment to explain.

In the article below, I wrote that the star Kappa Cas is moving through the galaxy at a stunning 1,100 km/sec. This turns out to be incorrect: The speed of the stellar wind blowing off its surface is that fast, but the star itself is moving far more slowly.


I based the original number off the NASA press release, which made that assumption about the speed. However, an email by astronomer Manfred Pakull set me straight. The star is actually moving relative to the Sun at about 25 km/sec, which means it’s moving around the galaxy at around the same speed we are.

Phil Plait Phil Plait


So why is there an arc of material compressed next to it instead of a more spherical shell of dust? The speed of the star is very small compared to the wind speed, so I’m guessing the dusty material the star’s wind is ramming is not evenly distributed. Note that the overall shape is more like part of a sphere as opposed to a bow wave, so this seems likely. Funny, too: When I read the press release I looked for journal papers on the star and found none (Pakull did mention one, which has some relevant numbers for the star). That’s surprising if it really is a runaway star, so now that anomaly makes more sense. Everything else I wrote below is correct, but note that the parts about it being a runaway are almost certainly incorrect. And also? It’s still gorgeous.








Zeta Oph

Photo by NASA/JPL-Caltech/UCLA




Rendering by SkySafari
