Astronomers at the University of Maryland (USA) have found that the X-rays emitted by jets of black holes change their brightness in just a few years. This challenges the widely held view that jet X-rays remain stable for millions of years. The discovery is reported in an article published in the journal Nature Astronomy.

The Chandra X-ray observatory, which has a high spatial and temporal resolution, has detected hundreds of radio jets (radio jets) that come from the poles of black holes that absorb interstellar matter and rush thousands of light-years into space located above or below the visible disk of the host galaxy. What came as a surprise to astronomers, however, was that many of the jets show an anomalously high and hard X-ray flux.

To explain the mechanism of generation of this radiation, the model of Compton backscattering of the cosmic microwave background (IC/CMB) was proposed. It requires the jets to maintain relativistic speed within thousands of light-years. Relatively low-energy particles inevitably scatter photons of the cosmic microwave background, transferring their energy to them, as a result of which X-rays are produced. However, any observed X-ray variability is inconsistent with IC/CMB.

The researchers analyzed archival data from the Chandra X-ray observatory, studying 53 extragalactic radio jets, including two jets in the galaxies M87 and Centaurus A. The scientists looked at 155 regions of X-ray jets, finding that the radiation behavior in 18 of them was not consistent with the IC / CMB model and varies from months to years.

The authors suggested that these changes can be explained by a synchrotron origin: the radiation is generated by a population of high-energy electrons of several teraelectronvolts concentrated in small regions of space. The presence of such populations, which occupy volumes much smaller than the cross section of the jet, presents a serious problem for theoretical models of particle acceleration over the entire volume of the jet. A likely cause of localized particle acceleration may be the reconnection of magnetic field lines in the jet, but the explanation of this phenomenon will be a task for future research.