An astrophysicist from the Hatfield-based University of Hertfordshire has helped discover the largest black hole jets ever recorded.

Professor Martin Hardcastle, an expert in radio astronomy and high-energy astrophysics, co-authored a paper in Nature revealing the biggest pair of black hole jets ever seen, which measure 23 million light-years in length.

This is equivalent to lining up 140 Milky Way galaxies back-to-back.

The jets were found as part of a sky survey which uncovered more than 10,000 of these faint megastructures.

They were detected using Europe's LOFAR (LOw Frequency ARray) radio telescope.

Professor Hardcastle said: "These giants were known before we started the campaign, but we had no idea that there would turn out to be so many.

"Usually when we get a new observational capability, such as LOFAR's combination of wide field of view and very high sensitivity to extended structure, we find something new, but it was still very exciting to see so many of these objects emerging."

The monstrous jet system, named Porphyrion after a giant in Greek mythology, dates back to when the universe was 6.3 billion years old.

It is located 7.5 billion light-years from Earth.

The jets, with a power output equivalent to trillions of suns, emanate from a supermassive black hole at the centre of a distant galaxy.

Professor Hardcastle added: "Martijn Oei's work has shown us that there isn't anything particularly special about the environments of these giant sources that causes them to reach those large sizes.

"My interpretation is that we need an unusually long-lived and stable accretion event around the central supermassive black hole to allow it to be active for so long—about a billion years—and to ensure that the jets keep pointing in the same direction over all of that time.

"What we're learning from the large number of giants is that this must be a relatively common occurrence."

The study, "Black hole jets on the scale of the cosmic web," was funded by several research councils, including the Dutch Research Council, the European Research Council, the UK Science and Technology Facilities Council, the UK Research and Innovation Future Leaders Fellowship, and the European Union.