The largest known black hole jets, measuring 23 million light-years across, have been detected in the distant universe. The pair of particle beams are being launched by a supermassive black hole that is more than a hundred times larger than our own galaxy, the Milky Way.
In 2022, we announced the discovery of one of the largest black hole jets in the night sky, emanating from a (relatively) nearby galaxy called NGC2663. Using CSIRO’s Australian Square Kilometre Array Probe (ASKAP) in Western Australia, we confirmed that NGC2663’s jet is one of the largest in the sky. In other words, it appears to be the largest jet as seen from Earth.
The new jet, published in the journal Nature, has been named “Porphyrion” (a giant from Greek mythology) by its discoverers at the California Institute of Technology in the US. It dwarfs NGC2663’s jet in actual size and is 20 times larger – a true giant.
Porphyrions can tell us more about the vast ecosystems of matter that flow inside and outside galaxies. But these jets also leave us scratching our heads: how can something 23 million light-years across be almost perfectly straight?
Seeing the invisible light
Porphyrion was discovered by astronomers using the international LOFAR Telescope, a network of radio sensors centered in the Netherlands that stretches from Sweden to Bulgaria and from Ireland to Latvia. Radio telescopes like ASKAP and LOFAR can see light that our eyes cannot see: radio waves.
First, what is creating this jet? At the center of the jet, the researchers saw a galaxy, and at the center of the galaxy, they found evidence of a supermassive black hole.
As matter is pulled toward the black hole, many different fates await. Some is consumed entirely. Some orbits the black hole, forming a disk. And some becomes twisted and tangled in the powerful magnetic field, until it is released into two opposing jets, exploding at nearly the speed of light.
We’ve seen black hole jets before, even ones that stretch millions of light years. What’s remarkable about Porphyrion is that it looks almost perfectly straight. There are plenty of curved, angled jets out there, including one seen by ASKAP called “The Dancing Ghosts.”
Straight in an incomprehensible way
Many processes can cause a jet to twist: an obstacle such as a dense cloud, a change in direction of a black hole, a strong magnetic field, an intergalactic “wind” as the host galaxy falls into a larger cosmic structure.
Porphyrion, on the other hand, seems to have been happily zipping through space for some 2 billion years without any problems.
This is confusing for two reasons. First, it is not from here. Its light has traveled about 7 billion years to reach Earth. We are seeing Porphyrion as it existed about 6 billion years after the Big Bang.
Like all astronomical objects, we’re seeing it in the past, when the universe was denser (remember: the universe is expanding). But a busy environment is the enemy of a straight jet stream.
Second, a jet that maintains a steady energy output for 2 billion years requires a steady food stream. But that implies a rich local environment, full of tasty treats (interstellar gas) ready to eat. This creates a paradox, because – again – a busy environment is the enemy of a straight jet.
As the researchers conclude, “how the jets can maintain such long-term coherence is currently unknown.” Perhaps Porphyrion was lucky enough to thread his jet through a quiet alleyway of intergalactic space.
There may be something about this ray that helps it stay focused. We don’t know. But we can figure out how to find out. The observer will explore the ray’s environment with further observations across the spectrum.
Radio astronomers are using telescopes like ASKAP and LOFAR to find more jets, so we can distinguish typical jets from random ones. Meanwhile, astrophysicists are using supercomputer simulations of jets to figure out what launches them, what might bend them, and under what conditions.
Objects like Porphyrion are not just strange objects in the universe. They are an integral part of the ecosystem of matter that forms our cosmic environment. Intergalactic matter nourishes galaxies, galaxies create stars, some galaxies even create black holes, black holes create a flow, the flow affects the intergalactic matter and us all over the place.
We are slowly discovering clues about our place in the universe.
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