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An X-ray telescope peered into the edge of a supernova remnant and found no tidy magnetic fields.
The edge of the supernova remnant RCW 86 is where the shock wave from a star's explosion slams into the surrounding gas. The IXPEtelescope looked at the southwestern part of this boundary in X-rays and tried to catch polarization — the way these rays oscillate. If the magnetic field behind the shock front were as smooth as a comb, the polarization would be strong. But the instrument saw no significant signal.
Instead, it managed to set upper limits: in bright regions, polarization does not exceed 15%, and in faint ones, 30–40%. This means the magnetic field there is not aligned in one direction even on scales of a fraction of a parsec (about three light-years). It looks more like a tangled ball of yarn than neat furrows.
X-ray polarization is like the direction of ripples on water: if the waves all go one way, the ripples are orderly, but if they slosh chaotically, no pattern is visible.
Such a mess in the magnetic field hints that the shock wave at this edge is moving slower than the material ejected in the explosion, yet still faster than direct measurements of speed from images suggest. It seems that reflected shock waves are at work here: they arise in rarefied regions of the ejected gas, not in the bright radio clumps. This helps us understand how a blast wave ages and fades, leaving behind whimsical patterns of gas and dust.
RCW 86 is one of the few supernova remnants that may be linked to a flare spotted by Chinese astronomers in 185 CE. The light from that explosion took more than eight thousand years to reach Earth.
In Stanislaw Lem's novel "Solaris," the planet's ocean spawns structures that defy simple geometric description, just as the magnetic fields in a supernova remnant refuse to line up into an understandable order.
