Black hole jets are powerful streams of particles and magnetic fields ejected from the regions surrounding supermassive black holes. These jets, often spanning hundreds of thousands of light-years, play a crucial role in shaping the environments around galaxies by injecting energy into the intergalactic medium. They can influence the growth of galaxies, the distribution of matter, and the magnetic fields within the cosmic web.

Now, researchers have found the biggest one to date.

So big we need to change the physics books

The newly discovered black hole-driven jets extend over 7 megaparsecs or 23 million light-years.

“This pair is not just the size of a solar system, or a Milky Way; we are talking about 140 Milky Way diameters in total,” says Martijn Oei, a Caltech postdoctoral scholar and lead author of a new Nature paper reporting the findings. “The Milky Way would be a little dot in these two giant eruptions.”

The megastructure was named Porphyrion, after a giant in Greek mythology. It has a total power output equal to trillions of suns, shooting from above and below a supermassive black hole at the heart of a remote galaxy.

What makes Porphyrion particularly remarkable is not just its size but also its coherence. The structure consists of a northern lobe, a core, and a southern jet, with hotspots at both ends — all of which are remarkably stable. The core of the system is anchored by a galaxy harboring a supermassive black hole which is actively accreting matter and powering the jets. The discovery of this structure raises new questions about how such jets manage to maintain their integrity over cosmic distances, even as the universe evolves.

The findings, based on observations using the International LOFAR Telescope (ILT) and the Giant Metrewave Radio Telescope (uGMRT) are so striking they force astrophysicists to rethink the limits regarding black hole energy transport and the stability of jets on a cosmic scale.

For decades, astronomers have studied these cosmic jets, with many falling within the size range of a few megaparsecs (Mpc). However, until now, the longest-known jet structures ended at about 5 Mpc. The discovery of Porphyrion, stretching to 7 Mpc, goes beyond this proposed limit.

These jets may be important for the universe

The jet dates from a time when our universe (currently 13.8 billion years old) was “just” 6.3 billion years old. During that time, the universe was denser and more turbulent than it is today, which makes it all the more surprising that the jets grew this big and lasted so long.

This suggests that these giant jet systems might have been influential in the formation of galaxies in the early universe.

“Astronomers believe that galaxies and their central black holes co-evolve, and one key aspect of this is that jets can spread huge amounts of energy that affect the growth of their host galaxies and other galaxies near them,” says co-author George Djorgovski, professor of astronomy and data science at Caltech. “This discovery shows that their effects can extend much farther out than we thought.”

Even the fact that there are so many of these jets (this is just the latest in a series of black hole jets) surprised researchers. This massive population of over 10,000 gargantuan jets was found using Europe’s LOFAR (LOw Frequency ARray) radio telescope.

“Giant jets were known before we started the campaign, but we had no idea that there would turn out to be so many,” says Martin Hardcastle, second author of the study and a professor of astrophysics at the University of Hertfordshire in England. “Usually when we get a new observational capability, such as LOFAR’s combination of wide field of view and very high sensitivity to extended structures, we find something new, but it was still very exciting to see so many of these objects emerging.”

Regular people helped with this study

The search for such large-scale outflows involved a combination of machine learning algorithms and the collective efforts of citizen scientists scanning the skies for large radio emissions. The team behind this discovery systematically analyzed data from the northern sky survey of the ILT, eventually uncovering Porphyrion.

Despite all this, there may be even more of these jets just waiting to be found — maybe even larger jets.

Statistical modeling based on the known population of jets suggests that the number of detectable Mpc-scale outflows may be much greater. With improved sensitivity from future radio surveys, astronomers may uncover many more of these colossal structures, further expanding our understanding of cosmic evolution.

“We may be looking at the tip of the iceberg,” Oei says. “Our LOFAR survey only covered 15 percent of the sky. And most of these giant jets are likely difficult to spot, so we believe there are many more of these behemoths out there.”

With more powerful telescopes on the horizon, we can anticipate the discovery of even larger and more energetic outflows, which will further illuminate the mysteries of the cosmic web and the forces that shape it.

The study was published in Nature https://doi.org/10.1038/s41586-024-07879-y.