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IXPE Reveals Origin of X-rays in Black Hole Jet

an international team of astronomers using NASA’s IXPE (Imaging X-ray Polarimetry Explorer) has identified the origin of X-rays in a supermassive black hole’s jet, answering a question that has been unresolved as the earliest days of X-ray astronomy. Their findings are described in a paper published in The astrophysical Journal Letters, by the American Astronomical Society, on November 11, 2023.

Unlocking the Secrets of the Perseus Cluster

The IXPE mission observed the Perseus cluster,the brightest galaxy cluster observable in X-rays,for over 600 hours during a 60-day period between January and March 2023. this represents IXPE’s longest observation of a single target to date and marks the first time the mission has studied a galaxy cluster.The Perseus Cluster is located approximately 250 million light-years away from Earth.

Focus on 3C 84

Specifically, the scientists studied the polarization properties of 3C 84, the massive active galaxy at the center of the Perseus Cluster. 3C 84 is a well-known and frequently observed X-ray source due to its proximity and brightness.Active galaxies like 3C 84 contain supermassive black holes that actively consume matter, releasing enormous amounts of energy.

the Challenge of X-ray Origins

The Perseus cluster contains a vast reservoir of X-ray emitting gas heated to temperatures comparable to the core of the Sun. for decades, astronomers have debated where these X-rays originate. Two main theories existed:

• Synchrotron Emission: X-rays are produced by high-energy electrons spiraling around magnetic field lines within the jet.
• Inverse Compton Scattering: Lower-energy photons (like those from the cosmic microwave background) are boosted to X-ray energies by interacting with the same high-energy electrons.

Distinguishing between these mechanisms requires understanding the polarization of the X-rays. Polarization refers to the direction of the electric field of light waves. Synchrotron emission typically produces highly polarized X-rays, while inverse Compton scattering generally results in lower polarization.

IXPE’s Breakthrough: Measuring Polarization

IXPE is uniquely equipped to measure the polarization of X-rays. By analyzing the polarization data from 3C 84, the team discovered that the X-rays are highly polarized.This finding strongly supports the synchrotron emission model. The data indicates that the X-rays are generated by electrons within the jet itself, not through interactions with external photons.

The use of multiple X-ray telescopes,especially the high-resolution imaging power of NASA’s Chandra X-ray Observatory,was essential to this discovery. Chandra provided detailed images of the jet structure, guiding IXPE’s observations.

What is Polarization and Why Does it Matter?

Polarization is a essential property of light that describes the direction of its oscillations. Think of a rope being shaken: it can be shaken up and down (vertical polarization), side to side (horizontal polarization), or at an angle. For X-rays, measuring polarization provides crucial information about the processes that create them.In the case of black hole jets, the degree of polarization reveals whether the X-rays are produced by electrons spiraling in magnetic fields (synchrotron emission) or by electrons boosting the energy of other photons (