Black holes twist their jets

Detailed view of the spiral plasma structures in blazar 3C 279. © NASA/DOE/Fermi LAT Collaboration; VLBA/Jorstad et al.; RadioAstron/Fuentes et al

A galactic nucleus in sight: The most detailed observation to date of a plasma jet from the vicinity of a supermassive black hole reveals complex twists of these gigantic structures in their area of ​​origin. The sharp insight is thanks to a virtual combination giant telescope, which was created by linking several units. The discoveries now shed new light on the formation and evolution of the mysterious cosmic jets of quasars and blazars, say astronomers.

They are among the brightest objects in the cosmos: Quasars are distant galactic nuclei in which central, supermassive black holes release enormous amounts of energy as they devour surrounding matter. In some of them you can also see a plasma jet that extends far into space. This is matter that is thrown away from the “plate” of the voracious black hole in the form of a jet at almost the speed of light. Special versions of these quasars with plasma jets are called blazars. The jet can be seen particularly clearly from Earth due to its favorable orientation.

A blazar seen through a virtual mega-telescope

The focus of the study by the international research team led by Antonio Fuentes from the Institute for Astrophysics of Andalusia (IAA-CSIC) in Granada was the blazar with the name 3C 279. In contrast to previous studies, the astronomers were now able to take a detailed look at it for the first time Structures in the area where the plasma jet is formed near the supermassive black hole. The data was provided by a very special astronomical construction, which was made possible by the space interferometer mission “RadioAstron”.

The crucial element was a space telescope in orbit around the Earth, which was active until 2019. For the study, its data was combined with that of 23 ground-based radio telescopes.

The RadioAstron mission enabled the virtual construction of a giant telescope. © Roscosmos

This resulted in a virtual telescope with an effective diameter of around 100,000 kilometers. The corresponding resolution power then enabled the scientists to take a detailed look at 3C 279. “Thanks to the RadioAstron space mission, we were able to obtain the highest-resolution image of the interior of a blazar to date, which now enabled us to observe the internal structure of the jet in detail for the first time,” says Fuentes.

Helical filaments revealed

As the team reports, a special pattern emerged in this area for the first time: The jet consists of at least two plasma strands twisted together that extend far into space. “This is the first time we have seen such filaments so close to the origin of the jet, and they tell us more about how the black hole shapes the plasma,” says co-author Eduardo Ros from the Max Planck Institute for Radio Astronomy in Bonn. His colleague Andrei Lobanov adds: “Similar spiral-shaped filaments have been observed in extragalactic jets before, but on a much larger scale, so it was assumed that they result from different parts of the flow moving at different speeds and shearing against each other.” said Lobanov.

But apparently the twists are not fundamentally due to subsequent influences: it is now clear that blazars do not emit straight and uniform plasma jets. However, the spiral-shaped structures in the source region show that the plasma is influenced in a special way by magnetic field forces around the black hole. Certain instabilities obviously play a role, say the astronomers. “A particularly fascinating aspect of our results is that they suggest the presence of a spiral magnetic field that confines the jet,” says co-author Guang-Yao Zhao from IAA-CSIC. “So it could be the magnetic field that rotates clockwise around the jet in 3C 279 that is used to steer and guide the jet’s plasma, which is moving at 0.997 times the speed of light,” explains the scientist.

However, according to the team of astronomers, more precise theoretical models are now needed to shed light on how the helical filaments can form and develop so close to the jet's origin. Lobanov concludes: “With this study, we enter a completely new territory in which these filaments can actually be linked to the most complicated processes in the immediate vicinity of the black hole that creates the jet,” says the scientist.

Source: Max Planck Institute for Radio Astronomy, specialist article: Nature Astronomy doi: 10.1038/s41550-023-02105-7

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