When I picture an exploding star in my head which I do unsurprisingly often the imaginary mental detonation I picture is symmetric. That is, it expands like a sphere, getting bigger in all directions equally.

Supernovae are actually not like that though. Stars are messy affairs, and when massive ones explode they tend to have internal factors that distort that nice, smooth expansion. One big factor is that the actual point of explosion is off-center in the star, not at its exact heart. That can create a massively asymmetric explosion, blasting vast amounts of material and energy off to one side.

Mind you, the core itself in such a star still collapses to become a super-dense neutron star (or a black hole), but the sideways nature of the explosion can give a kick to the leftover ball of neutrons. Quite a kick. In fact, the energies are so titanic that an off-center supernova explosion can blast the neutron star in the other direction, screaming away from the explosion site like a shell out of the muzzle of a battleship gun.

And now astronomers may have found the most extreme example of this: what looks to be just such a neutron star barreling away from a supernova at high speed:

[Click to Chandrasekharenate.]

This image is a combination of observations from the XMM-Newton and Chandra X-ray observatories, the Digitized Sky Survey, and the 2MASS infrared survey. It shows the supernova remnant SNR MSH 11-16A, located about 30,000 light years away. The purple glow is from X-rays emitted by the gas superheated to millions of degrees by the exposion.

But look off to the right. See that comet-looking thing? Ive put a close up of it here. You can see a dot at the head of the “comet”: astronomers think that might be the runaway neutron star from the explosion that created SNR MSH 11-16A! Its hard to know for sure, but a lot of things add up to make me think theyre right.

The most obvious is that tail of gas pointing right back to the center of the supernova gas cloud. A hot, young neutron star blows out a high-energy wind of subatomic particles called a pulsar wind, and that pushes against gas floating out in space. As a runaway neutron star blasts through space, it would leave a glowing trail like that. The X-rays appear to be coming from a single, tiny point, just what youd expect for a neutron star, and observations using optical and infrared dont see it; again, just what youd expect since neutron stars are tiny and dont glow visibly. Theyre brightest in X-rays due to their phenomenally strong magnetic fields whipping particles around at high energies.

The fainter tail to the side is something of a mystery, though. Apparently things like this have been seen before, but its not clear whats causing it.

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