NASA IXPE’s Longest Observation Solves Black Hole Jets Mystery

Written by Michael Allen

An international team of astronomers using NASA’s Imaging X-ray Polarimetry Explorer (IXPE) has identified the origin of

The IXPE mission observed the Perseus Cluster, the brightest galaxy cluster observable in X-rays, for more than 600 hours over a 60-day period between January and March. Not only is this the longest observation of a single target by the IXPE to date, but it is also the first time the IXPE has observed a galaxy cluster.

Specifically, the team of scientists studied the polarization properties of 3C 84, the massive active galaxy located at the very center of the Perseus cluster. This active galaxy is a well-known X-ray source and a common target for X-ray astronomers due to its proximity and brightness.

Because the Perseus cluster is so massive, it hosts a huge reservoir of X-ray emitting gas as hot as the Sun’s core. The use of multiple X-ray telescopes, particularly the high-resolution imaging power of NASA’s Chandra X-ray Observatory, proved key to unraveling the signals contained in the IXPE data. The scientists combined these X-ray measurements with data from the agency’s NuSTAR (Nuclear Spectroscopic Telescope Array) mission and the Neil Gehrels Swift Observatory.

• Polarization measurements from IXPE contain information about the orientation and alignment of emitted X-ray light waves. The more synchronized the X-ray waves move, the greater the degree of polarization.
• X-rays from an active galaxy like 3C 84 are thought to come from a process known as inverse Compton scattering, in which light bounces off particles and gains energy. IXPE polarization measurements allow us to identify the presence of either inverse Compton scattering or other scenarios.
• “Seed photons” is the term for the lowest energy radiation subject to the energizing process of inverse Compton scattering.
• You may remember the Perseus Cluster from this sonification reproducing the sound of a black hole from May 2022.

“Although measuring the polarization of 3C 84 was one of the main scientific goals, we are still looking for additional polarization signals in this galaxy cluster that could be signatures of more exotic physics,” said Steven Ehlert, IXPE project scientist and astronomer at NASA’s Marshall Space Flight Center in Huntsville.

“We have already determined that for sources like 3C 84, the X-rays come from inverse Compton scattering,” said Ioannis Liodakis, a researcher at the Institute of Astrophysics – FORTH in Heraklion, Greece, and lead author of the paper. “With the IXPE observations of 3C 84, we had a unique opportunity to determine the properties of the seed photons.”

The first possible origin scenario for seed photons is known as a self-Compton synchrotron, in which lower-energy radiation comes from the same jet that produces the high-energy particles.

In the alternative scenario known as outer Compton, the seed photons come from background radiation sources unrelated to the jet.

“The Compton self-synchrotron and Compton external scenarios have very different predictions for their X-ray polarization,” said Frédéric Marin, an astrophysicist at the Strasbourg Astronomical Observatory in France and co-author of the study. “Any detection of X-ray polarization from 3C 84 almost decisively rules out the possibility of an external Compton as the emission mechanism.”

Throughout the 60-day observing campaign, optical and radio telescopes around the world turned their attention to 3C 84 to further test between the two scenarios.

NASA’s IXPE measured a net polarization of 4% in the X-ray spectrum, with comparable values ​​measured in optical and radio data. These results strongly favor the auto-Compton synchrotron model for seed photons, where they come from the same jet as the higher energy particles.

“Separating these two components was critical to this measurement and could not be done by a single

Scientists will continue to analyze IXPE data from different locations in the Perseus cluster to detect different signals.

NASA’s IXPE, which continues to provide unprecedented data enabling groundbreaking discoveries about celestial objects across the universe, is a joint mission of NASA and the Italian Space Agency with scientific partners and collaborators in 12 countries. The IXPE mission is led by NASA’s Marshall Space Flight Center in Huntsville, Alabama. BAE Systems, Inc., headquartered in Falls Church, Virginia, manages spacecraft operations in collaboration with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

Learn more about IXPE’s current mission here:

https://www.nasa.gov/ixpe