Scientists see black hole jet in a new light
- A supermassive black hole in giant galaxy Centaurus A is shooting a powerful stream of energy, called a “jet,” out into space.
- Scientists studied bright spots, or “knots,” in this jet and found that some move almost as fast as light! They even look like they’re moving faster than light, but this is just because of the way we see them from Earth.
- This discovery helps scientists learn more about how black holes work, and they plan to study similar jets in other galaxies too.
A new approach to studying a black hole jet
Researchers led by the University of Michigan have pored over more than two decades of data from NASA’s Chandra X-Ray Observatory, looking closely at the high-energy jet of particles being blasted across space by the supermassive black hole at the center of the giant galaxy Centaurus A.
The new study is the latest effort in a small but growing body of research that’s digging deeper into data to spot subtle, meaningful differences between radio and X-ray observations.
David Bogensberger, lead author and a postdoctoral fellow at U-M said:
A key to understanding what’s going on in the jet could be understanding how different wavelength bands [for example, differences between the X-ray data and the radio data] trace different parts of the environment.
Bogensberger explained:
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 colleagues published their findings on October 18, 2024, in The Astrophysical Journal.
The video below, from NASA, shows what we knew about the galaxy Centaurus A – and its central black hole and jet – a decade ago:
Knots in the jet
In the new study, the Michigan team developed a computer algorithm to look at Chandra’s observations of Centaurus A from 2000 to 2022. The algorithm tracked bright, lumpy features in the jet, called “knots” by scientists. By following knots that moved during the observation period, the team could then measure their speed.
The speed of one knot was particularly remarkable. In fact, it appeared to be moving faster than the speed of light! The speed of light is 186,000 miles per second (300,000 km/s). Faster-than-light speed is impossible, according to modern physical laws. But this knot has the appearance of superluminal speed due to its motion relative to Chandra’s vantage point near Earth. The distance between the knot and Chandra shrinks almost as fast as light can travel.
Still, the knot is moving fast! The team determined its actual speed is at least 94% the speed of light. A knot in a similar location previously had its speed measured using radio observations. That result clocked the knot with a slightly slower speed, about 80% of the speed of light. Bogensberger said:
What this means is that [knots in the jet visible at radio wavelengths, and knots visible at X-ray wavelengths] move differently.
New insights from the knots
That’s a big clue as to what these knots might be, and how they behave. And that finding wasn’t the only one that stood out from the data.
For example, radio observations of knots suggested the structures closest to the black hole move the fastest. In the new study, however, Bogensberger and his colleagues found the fastest X-ray knot in a sort of middle region. It wasn’t the farthest from the black hole, but it wasn’t the nearest to it either. Bogensberger said:
There’s a lot we still don’t really know about how jets work in the X-ray band. This highlights 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.
The jet in Centaurus A is special to us because it’s the closest supermassive black hole jet we know, at about 12 million light-years away. This relative proximity makes it a good first option for testing and validating new methodology.
But, for his part, Bogensberger will be stepping further out from here, using the team’s approach to examine other supermassive black hole jets, in other, more distant galaxies. Features like knots become more challenging to resolve in jets that are farther away. Bogensberger added:
But there are other galaxies where this analysis can be done. And that’s what I plan to do next.
Bottom line: There’s new science to discover around black holes. A new study looked at the high-energy jets blasted across space by the supermassive black hole at the center of the galaxy Centaurus A. They travel at least 94% of the speed of light.
Source: Superluminal Proper Motion in the X-Ray Jet of Centaurus A
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