At the center of galaxy NGC 4278 sits a black hole that shoots out two plasma jets, like a giant cannon firing particles into space. These jets accelerate particles to energies that no earthly accelerator could ever dream of. Recently, the LHAASO observatory caught very high-energy radiation from this galaxy — the kind that is born when particles in the jet collide with something and transfer energy to light.
The Swift telescope monitored the galaxy and saw that it behaves quietly: the X-ray flux is weak, like smoldering coals. But when scientists tried to explain all the radiation with a single simple model, saying electrons in the jet illuminate themselves, they got too little. To make ends meet, they would have to assume the jet is flying toward us at a breakneck speed, almost faster than light. That's strange.
So the authors tried another scenario. Around the black hole there is a faint but hot disk: it doesn't shine brightly but emits many invisible photons. Electrons in the jet collide with these photons and boost their energy, like a tennis racket boosting a ball. This "external" light explains everything without crazy speeds and with moderate jet power.
The scientists calculated how many neutrinos the IceCube detector could catch over 15 years. In the external light scenario, it comes out to about 0.001 neutrinos — meaning, most likely, none. But if the jet has more protons than assumed, or the galaxy occasionally flares up, the chances increase. Future observations will help determine whether such faint galaxies are truly hidden neutrino factories.
Neutrinos are so elusive that every second, trillions of these particles from the Sun pass through your fingernail, and you don't feel a thing.
In the novel "The Three-Body Problem," aliens use particles accelerated to relativistic speeds for communication — much like galaxy jets carry information about their black holes.