Just beyond the Local Group of galaxies that surround our Milky Way, where our map of the cosmos once plunged off an edge and into the unknown, lurks a galactic sea monster.
Weirdo galaxy NGC 4258 has two extra tentacles reaching out from its middle – part of a system that could one day drive or quench a revolution in physics.
It was 1961 when astronomers discovered the two anomalous arms in NGC 4258, which is 25 million light years away. They defied explanation. Unlike the arms in other spiral galaxies, which wind around in the same plane like the coils of a nautilus shell, these protruded out of the disc of the galaxy.
That was weird enough. But it turns out that the extra arms were just one part of an intricate machine unspooling from the middle of the galaxy – a structure now teaching us about everything from black holes to the expansion of the universe.