Precession Responsible for the Mysterious Radio Flares of Galactic Nuclei

Saturday - September 2 2023, 02:04 UTC - 1 year ago

A recent study has proposed that the precession of an AGN jet could be responsible for the mysterious flares and curvature of galactic nuclei, suggesting that a binary black hole is the cause. Multiple observatories have been used to confirm this and there are now clear implications for deciphering the secrets of the binary supermassive black holes.

In the celestial tapestry of active galactic nuclei (AGN), a class of objects known as "blazars" has long captivated astronomers. Blazars make their cosmic debut when one of their emitted jets points directly towards the Earth. For years, scientists believed that the frequent and significant surges in brightness in blazars, often referred to as flare activity, were intimately tied to the ejection of jet components from the core, resulting in enhanced emissions. However, a recent study published in The Astrophysical Journal challenges this conventional wisdom.

The crucial role of precession .

Traditionally, variations in brightness and their enigmatic, meandering jet structures were thought to result from the ejection of jet components from the core. Yet, as researchers accumulated detailed observations over the years, a more complex and intricate picture emerged, casting doubt on this simplified explanation.

The recent paper introduces an alternative hypothesis. Silke Britzen, the lead author from the Max Planck Institute for Radio Astronomy in Bonn, Germany, proposes that the precession of the jet source might hold the key. When these jets swirl due to precession, they introduce periodic changes in intensity, a phenomenon known as the Doppler effect. Notably, this precession-driven variability has been observed in multiple AGN jets. In a prior study focused on OJ 287, a prime candidate for hosting a supermassive black hole binary, Britzen's team established that the variations in brightness and jet bending originate from precession.

The researchers extended their investigation to 12 prominent AGNs to validate their theory. Their findings provided compelling evidence that the observed brightness variations and jet curvature could indeed be attributed to precession. While the researchers do not dismiss the role of internal interactions within the jet, they suggest that jet precession plays a pivotal role in modulating and altering the appearance of these cosmic jets. It's this precession that endows them with their characteristic curvy and luminous demeanor.

One of the study's most profound implications is that jet curvature could serve as a crucial signature for the presence of binary black holes at the centers of galaxies. The gravitational influence of a second black hole on the jet-emitting black hole compels the jet to take on its meandering path. Furthermore, the research team detected traces of a smaller amplitude nutation motion in the radio light curves and jet component kinematics, providing additional support for the role of precession.

Like 'simple gyroscopes' .

"Physics of accretion disks and jets is rather complex, but their bulk kinematics can be compared to simple gyroscopes," said co-author Michal Zajaček from the Masaryk University (Brno, Czech Republic) in a press release. "If you exert an external torque on an accretion disk, for instance by an orbiting secondary black hole, it will precess and nutate, and along with it the jet as well, similar to the Earth's rotation axis that is affected by the Moon and the Sun." .

To achieve this detection, Britzen and her colleagues utilized international radio observatories such as the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA) of the National Radio Astronomy Observatory to track the galactic nuclei in the sample.

The authors' findings will have enduring implications for our understanding of AGN activity, and present the perfect opportunity to unlock the secrets of binary supermassive black holes.