Astronomers have observed a pair of black hole jets spanning an astonishing 23 million light-years. To put that into perspective, it's like aligning 140 Milky Way galaxies in a row.
"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 Nature paper reporting the findings. "The Milky Way would be a little dot in these two giant eruptions."
The Porphyrion jet formation, named after a figure in Greek mythology, can be traced back to when the universe was approximately 6.3 billion years old, less than half its current age of 13.8 billion years. These jets release energy outputs akin to trillions of suns as they surge forth from above and below a supermassive black hole located within a remote galaxy
A Record-Breaking Discovery
Before the discovery of Porphyrion, the most extensive jet system documented was Alcyoneus, also named after a giant from mythology. This jet system, uncovered in 2022 by the same research team that found Porphyrion, spans an area roughly equivalent to 100 Milky Way galaxies. In comparison, the well-known Centaurus A jets, the closest major jet system to Earth, cover a distance of about 10 Milky Ways.
The recent discovery hints at the possibility that these immense jet systems may have played a larger role in shaping galaxies in the universe than previously thought. During its existence, Porphyrion existed when the intricate threads of the cosmic web connecting and supporting galaxies were more closely interwoven than they are today. This suggests that jets like Porphyrion could have an impact on a larger region of the cosmic web compared to jets seen in our nearby universe.
What Are Black Hole Jets?
Supermassive black holes residing at the centers of certain galaxies unleash jets of energy and particles that travel at nearly the speed of light. The immense gravitational pull of these black holes draws matter toward them as they feast on surrounding gas and debris. However, instead of being consumed, a small portion of the particles is propelled to speeds nearing that of light and ejected in two focused streams aligned with the black hole's axis of rotation. These jets are believed to be responsible for producing the universe's fastest-moving particles, known as cosmic rays.
"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 further than we thought."
A Glance at the Past
To trace back the origin of Porphyrion, researchers employed the Giant Metrewave Radio Telescope (GMRT) located in India and supplemented their findings with data from the Dark Energy Spectroscopic Instrument (DESI) project based at Kitt Peak National Observatory in Arizona. These observations led them to identify the source of the jets as a massive galaxy approximately 10 times more massive than our Milky Way.
Additionally, the team utilized the W. M. Keck Observatory in Hawai'i and determined that Porphyrion is situated 7.5 billion light-years away from Earth. "Up until now, these giant jet systems appeared to be a phenomenon of the recent universe," Oei says.
"If distant jets like these can reach the scale of the cosmic web, then every place in the universe may have been affected by black hole activity at some point in cosmic time."
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