# When a fast-moving star goes supernova, how will the resulting remnant evolve?

Let's take a massive star that has zero velocity. When this star goes supernova, the resulting supernova remnant will expand in a sphere. But, let's take a runaway star travelling at 200 km/s. I am predicting that the remnant will form a teardrop shape, with the rounded edge compressed a little with the rear end elongated.

My reasoning is that the material ejected "forwards" relative to the star's velocity vector will gain some velocity, leaving the dead star behind. However, the material ejected backward will lose velocity, meaning that it will stream out over a longer distance. So to a viewer it would look like a "cosmic fireball" in some sense.

Is this correct, and would there be anything that could change this result? If I am wrong, what would be the actual way that the remnant would expand?

• By "fast-moving" I assume you mean "relative to the surrounding interstellar medium". My guess would be that the velocity of the expanding gas (10000km/s?) is so much faster that the initial velocity of the star is relatively insignificant. (only a guess) Feb 13, 2021 at 23:29
• Also note that supernova explosions have a high probability of being quite asymmetrical, not neatly spherical explosions, and the remnant can receive a sizeable kick. Eg, Pulsar B1508+55 is moving at ~1000 km/s & it's possible that some pulsars have speeds around 1500 km/s. See arxiv.org/abs/astro-ph/0509031 Feb 14, 2021 at 3:52
• Also, assuming the supernova is spherically symmetric, the supernova remanent will remain symmetric wrt its star. An anisotrpy can only happen due to interaction with the ISM which might slow down the ejected gas somewhat in one side or when the supernova is not symmetric, thus net momentum is transferred to the stellar remanent Feb 14, 2021 at 12:46