Martin Oei (California Institute of Technology) / Dylan Nelson (IllustrisTNG collaboration).
Supermassive black holes at the centres of galaxies aren’t just decorative. As they refuel, the powerful radiation they emit drives away gas and dust that would otherwise form stars, providing a feedback that limits the growth of galaxies. But the influence of black holes can reach beyond the galaxy in which they reside. Many black holes produce jets, and in the case of supermassive black holes, these jets can eject material outside the galaxy entirely.
Now, researchers are getting a clearer picture of just how far the effects reach beyond our galaxy: A new study describes the largest jets ever observed, stretching a total of 23 million light-years (7 megaparsecs) away—a distance that could easily send the jets hurtling material into other galaxies or even the cosmic web of dark matter that makes up the universe.
Extreme Jet
Jets form in complex environments near black holes. The intense heat of the infalling matter ionizes and heats it, generating an electromagnetic field that acts as a natural particle accelerator. This produces jets of particles traveling at a significant fraction of the speed of light. These eventually collide with nearby material, creating shock waves that heat and accelerate that material as well. Over time, this leads to a massive, coordinated outflow of matter, the scale of the jet proportional to a combination of the size of the black hole and the amount of material it feeds.
Typically, black holes form jets at each pole, resulting in a pair of outflows moving in opposite directions. We have seen many such examples at different scales, from stellar-mass black holes to supermassive black holes capable of forming quasars, the most luminous objects in the Universe.
The discovery of the new jet is the result of a systematic search for large jets at radio wavelengths at an observatory called LOFAR (Low Frequency Array), which covers part of the Northern Hemisphere sky. Data from the telescope was scanned using a combination of machine learning and citizen scientist volunteers. The program has identified more than 11,000 jets covering distances of megaparsecs (a parsec is just over three light years). A paper published Wednesday describes the largest of these jets, which it names Porphyrion after a giant in Greek mythology.
Initial follow-up observations led to the discovery of the galaxy: two objects were found in roughly the right position, one of which had a lobe that extended along the axis of the jet, making it the most likely source. The galaxy is roughly 10 times more massive than the Milky Way, and spectroscopy indicates that we are observing conditions as they existed about 6 billion years after the Big Bang, more than half the time before the present.
