The study centers on the high-energy jet of particles ejected from the supermassive black hole at the core of the galaxy Centaurus A. Black hole jets are observable across various wavelengths, with telescopes capable of detecting both radio waves and X-rays. Since Chandra's deployment in 1999, astronomers have noted unusually bright X-ray emissions from these jets, which has sparked significant interest.

However, until now, X-ray observations seemed to replicate similar features observed in radio wavelengths, which limited the discovery of unique jet properties.

Black hole jets are vast cosmic phenomena - sometimes larger than their host galaxies - yet they still hold many mysteries. According to David Bogensberger, the study's lead author and a postdoctoral fellow at the University of Michigan, "A key to understanding what's going on in the jet could be understanding how different wavelength bands trace different parts of the environment. Now we have that possibility."

This research contributes to a growing field of studies that delve into subtle, yet significant, variations between radio and X-ray jet data. Bogensberger noted, "The jet in X-rays is different from the jet in radio waves. The X-ray data traces a unique picture that you can't see in any other wavelength."

Bogensberger and an international team of collaborators published their findings in *The Astrophysical Journal*. They utilized Chandra's observations of Centaurus A from 2000 to 2022. To analyze the data, Bogensberger developed an algorithm that tracked specific bright features within the jet, known as knots, over time. This enabled the team to measure their speed as they moved through space.

One knot stood out in particular. It appeared to move faster than the speed of light when viewed from Chandra's position near Earth - a phenomenon attributed to its rapid approach relative to Chandra's perspective. The researchers determined that the knot's actual speed was about 94% of light speed, far exceeding previous radio observations, which estimated a slower speed of approximately 80% of light speed.

"What this means is that radio and X-ray jet knots move differently," Bogensberger explained.

Further differences emerged in the study's findings. While radio data suggested that knots closest to the black hole moved the fastest, Bogensberger's team found the fastest knot in a middle region - neither closest to nor farthest from the black hole.

"There's a lot we still don't really know about how jets work in the X-ray band," Bogensberger said, emphasizing the need for further research. "We've shown a new approach to studying jets, and I think there's a lot of interesting work to be done."

Looking ahead, Bogensberger plans to apply this methodology to study jets in other galaxies. Centaurus A's jet, located approximately 12 million light years away, was an ideal initial target due to its relative closeness, which allowed for clearer observation of the jet's features.

"But there are other galaxies where this analysis can be done," Bogensberger noted. "And that's what I plan to do next."

Research Report:Superluminal proper motion in the X-ray jet of Centaurus A

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