In the galaxy NGC 1566, located in the constellation Dorado, there is an active nucleus — a supermassive black hole surrounded by a cloud of fast-moving gas. As the gas falls toward the hole, it heats up and emits bright spectral lines. Sometimes these lines become very broad — a sign of the gas's rapid rotation. But in NGC 1566, the broad lines appear and disappear, as if someone is flipping a switch.
Astronomers set out to figure out what is hiding these lines. They used a technique similar to polarized sunglasses: light from the galaxy's nucleus passes through a special filter that reveals how the electromagnetic wave oscillates. If a dense dust cloud were hiding the lines, the light around it would acquire a characteristic polarization. But observations with the VLT telescope in Chile showed no such effect. So it's not an eclipse.
Moreover, the polarization behaved opposite to expectations: when the galaxy was brighter, the polarization was stronger, and its direction was perpendicular to the rotation axis. This suggests that the gas cloud itself, which produces the broad lines, temporarily contracted or dispersed — possibly due to changes in the flow of matter falling onto the black hole. Galaxy NGC 1566 continues to surprise, reminding us that even the most powerful "beacons" of the universe do not always shine the same way.
NGC 1566 is one of the brightest Seyfert galaxies in the sky; it can even be seen with an amateur telescope.