Astronomy doesn't just use telescopes to observe space, it uses many types of cosmic “messenger” to help us understand what is happening out there. We have dishes catching radio waves, observatories for gravitational waves and, more recently, sophisticated experiments detecting neutrinos, the most elusive fundamental particle.
Neutrinos have no electric charge and a tiny mass, which allows them to move through anything unimpeded. Over 600 trillions neutrinos pass through your body every second, most of them coming from the Sun. The ghostly particles are produced in many processes, and the most powerful of them can easily cross intergalactic distances before being detected.
These high-energy neutrinos were detected for the first time last summer by the IceCube Neutrino Observatory in Antarctica, and now researchers have linked this special neutrino detection to its likely source: collisions between particle jets from a supermassive black hole in the radio galaxy TXS 0506+056. Their findings are published in Astronomy & Astrophysics.
The radio galaxy in question is full of energetic processes, like an active supermassive black hole emitting jets, but it is not a unique galaxy, we know many other objects just like it. The researchers reasoned that the production of such an energetic neutrino must have a more peculiar cause.
“It was a bit of a mystery why only TXS 0506+056 has been identified as a neutrino emitter,” lead author Silke Britzen from the Max Planck Institute for Radio Astronomy, said in a statement. “We wanted to unravel what makes TXS 0506+056 special, to understand the neutrino creation process and to localize the emission site, so [we] studied a series of high-resolution radio images of the jet.”
The images revealed complex interactions between the material released by the jet. One explanation has the material from an older jet being hit by a newer jet. Or maybe it is two jets from the same source that are interacting. Either scenario strongly suggests that the energetic processes from the jets are the cause of the neutrino emission.
Supermassive black hole jets are seen in many galaxies and they often extend up to a million light-years from the emitting black hole. In the case of TXS 0506+056, which is located 3.8 billion light-years away, the complexity might be due to having a binary supermassive black hole system. These systems can happen during a galaxy collision, and some of the observations from this study suggest that this may be the case for this object.
While this “multi-messenger” type of astronomy is still in its infancy, this and other discoveries of the last few years show its potential to dramatically expand our understanding of the universe.