The black hole GS 1354-64 in the constellation Musca woke up in 2025 and began greedily pulling matter from its companion star. The orbiting X-ray telescope IXPE caught it at a rare moment: the outburst had already subsided, but the system had not yet settled down. Like a person frozen on a doorstep, it lingered between two states — calm and turbulent.
The light from the black hole's vicinity turned out to be polarized: that is, its waves vibrated not randomly but in a single direction. A crowd that first moves chaotically and then suddenly falls into step. The fraction of such "aligned" photons was 4%, and the higher their energy, the more orderly their march. At the highest energy, polarization reached 11%.
It turned out that both sources are at work. The hot disk, like a pancake, emits with one wave orientation, while the corona, a cloud of plasma above the disk, emits with another, rotated by 90 degrees. Their light mixes, and the overall picture depends on which is brighter. That's the key: the black hole can't decide which state to be in, so we see their struggle.
Such observations are like an X-ray compass for astronomers. It shows where matter flows are directed and how the black hole's appetite changes. GS 1354-64 froze on the threshold, and that's exactly what allowed us to peek into its inner kitchen.
X-ray polarization from black holes is such a subtle phenomenon that the first dedicated satellite to measure it was launched only in 2021. Before that, astronomers spent nearly half a century merely guessing about the geometry of accretion disks.
In the movie Interstellar, the glowing disk around the black hole Gargantua looks flat and smooth. Polarization observations show that in reality, chaos boils there from two sources with different wave orientations.