Astrophysics: How black holes produce bright light

Observations of brightly shining jets of particles from galaxies powered by supermassive black holes, published in Nature this week, shed light on the processes that underlie such phenomena. The findings may help us to understand more about high-energy emission processes from black-hole systems.

Blazars are a type of galaxy from which powerful jets of ionized matter are released pointing in the direction of Earth. Most of the light from blazars is produced by high-energy particles. How these particles are accelerated to such high energies remains an unanswered question. X-ray measurements of the jets offer the possibility to answer this question, but an instrument capable of making such measurements has not been available until recently.

Launched in December 2021, the Imaging X-ray Polarimetry Explorer (IXPE) has measured the X-ray polarization of a very bright blazar known as Markarian 501 (Mrk 501). Ioannis Liodakis and colleagues consider two X-ray polarimetry observations of Mrk 501 made by IXPE in March 2022. By comparing these measurements with radio and optical polarimetric data, the authors propose that the initial acceleration of particles in the jets from this blazar was caused by a shock wave that propagated out along the jet. These results demonstrate how using different measurements of polarization can probe the condition in supermassive black-hole systems.

In an accompanying News & Views, Lea Marcotulli describes these results as a turning point in our understanding of blazars. “X-ray polarimetry will now enable us to study several of these jets to understand if these shocks are common to all sources”, they add.