A supermassive black hole, unleashing powerful astrophysical jets into space, has created the largest galactic structure ever observed.

Dubbed "Porphyrion," after the Greek king of giants, this colossal formation spans an astonishing 7 megaparsecs, or 23 million light-years across. It's a significant component of the cosmic web that connects the Universe.

"Porphyrion demonstrates the interconnectedness of the cosmos," explained astronomer Martijn Oei of Leiden University and Caltech. "This single black hole has produced a structure comparable in scale to cosmic filaments and voids. Imagine a tiny amoeba generating a powerful fountain the size of Earth!"

This remarkable discovery, following the discovery of Alcyoneus with its 16-million-light-year jets, suggests that the ingredients for these 'impossible' black hole jets may be more common than previously thought.

Astrophysical jets, powered by black holes, are still not fully understood. When a black hole feeds, some material from the surrounding accretion disk is diverted along magnetic field lines to the poles, where it is launched into space as high-speed jets of plasma and magnetic field.

These jets are ubiquitous in the Universe, but the jets of Alcyoneus and Porphyrion pose unique challenges.

To generate such massive jets, a black hole needs to feed continuously for billions of years, requiring a vast reservoir of material. Additionally, the extreme length of these jets presents stability issues. As jets grow longer, they become more prone to instabilities that can disrupt their structure.

"Numerical simulations suggest that jets are inherently unstable," Oei added. "Disturbances tend to grow and eventually destroy the jet. The limited fueling time and magnetohydrodynamic instabilities likely set an upper limit to jet growth, although we're unsure of its exact value."

The stability of Alcyoneus and Porphyrion's jets over such vast distances remains a mystery. However, they could offer clues about the cosmic web's structure. The jets' length suggests they may play a role in shaping the cosmic web, influencing the high temperatures and magnetic field structures observed in voids.

These mega-jets could have been more common in the early Universe, when black holes were often in a radiative mode. They may have played a significant role in sculpting the cosmic web during this era. Even today, the cosmos might be teeming with such galaxies.

"I believe galaxies with giant jets are more common than we realize," Oei stated. "As these jets grow larger, they become harder to observe, especially in the distant Universe. Improved instrumentation will likely reveal many more of these galaxies."

The discovery of Alcyoneus and Porphyrion opens up new avenues for research and offers hope for unraveling the mysteries of these astonishing cosmic phenomena.

Sources: Published 18 September 2024 in Nature; Black hole jets on the scale of the cosmic web https://www.nature.com/articles/s41586-024-07879-y

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