NASA's Imaging X-ray Polarimetry Explorer (IXPE) has helped astronomers solve a decades-old mystery about the origin of X-rays from powerful jets produced by supermassive black holes. The findings were published on November 11 in The Astrophysical Journal Letters by the American Astronomical Society.
An international team of scientists carried out IXPE's longest-ever observation of a single object, studying the Perseus Cluster for more than 600 hours over a 60-day period between January and March. This also marked the first time IXPE observed a galaxy cluster.
At the center of the Perseus Cluster lies 3C 84, an active galaxy known for its bright X-ray emissions. Researchers focused on measuring the polarization of X-rays from this galaxy, which provides key clues about how the radiation is produced. To separate the galaxy's signal from the surrounding hot gas, scientists combined IXPE data with observations from NASA's Chandra X-ray Observatory, NuSTAR, and the Neil Gehrels Swift Observatory.
"While measuring the polarization of 3C 84 was one of the key science goals, we are still searching for additional polarization signals in this galaxy cluster that could be signatures of more exotic physics," said Steven Ehlert, project scientist for IXPE and astronomer at NASA's Marshall Space Flight Center in Huntsville.
The study found a net X-ray polarization of about 4%, closely matching polarization levels seen in optical and radio observations. These results strongly support the synchrotron self-Compton model, in which X-rays are produced when lower-energy light from the same jet interacts with highly energetic particles.
Scientists say the findings rule out alternative explanations and confirm how X-rays are generated in black hole jets. Further analysis of IXPE data from other regions of the Perseus Cluster is ongoing.
