The leading model of particle acceleration is challenged as black hole jet’s X-ray emissions unexpectedly vary.

Researchers discovered relatively recently that black hole jets emit X-rays, and how the jets accelerate particles to such a high-energy state remains a mystery. Surprising new results in natural astronomy It seems to rule out one leading theory, opening the door to a reimagining of how particle acceleration works in jets — and perhaps also elsewhere in the universe.

A leading model of how jets generate X-rays predicts that jets’ X-ray emissions remain stable over long periods of time (millions of years). However, the new paper found that the X-ray emissions of a statistically significant number of aircraft differed over just a few years.

“One of the reasons we’re so excited about variance is that there are two main models for how X-rays are produced in these jets, and they’re very different,” explains lead author Elaine Meyer, an astronomer at the University of Maryland. , Baltimore County. “One model calls for very low-energy electrons and the other contains very high-energy electrons. And one of those models is completely incompatible with any kind of asymmetry.”

For the study, the authors analyzed archival data from the Chandra X-ray Observatory, the highest-resolution X-ray observatory available. The research team looked at nearly all of the black hole’s jets for which Chandra had multiple observations, which amounted to 155 unique regions within 53 jets.

Detecting relatively frequent variation on such short time scales “is revolutionary in the context of these jets, because that was totally unexpected,” Meyer says.

Rethink particle acceleration

In addition to assuming stability in X-ray emissions over time, the simplest theory of how jets generate X-rays assumes that particle acceleration occurs at the galactic center in the black hole “engine” that drives the jet. However, the new study found rapid changes in X-ray emissions along the planes. This indicates that particle acceleration occurs along the plane, at great distances from the origin of the plane at the black hole.

“There are theories about how this might work, but a lot of what we’ve been working with now is clearly inconsistent with our observations,” says Meyer.

Interestingly, the results also indicated that jets closer to Earth had greater diversity than jets farther away. The latter is so far away that, by the time the light from it reaches the telescope, it is like looking back in time. It makes sense to Meyer that older planes would have less turbulence. Earlier in the history of the universe, the universe was smaller and the surrounding radiation was larger, which the researchers believe could lead to greater stability of X-rays in jets.

Crucial collaboration

Despite Chandra’s impressive imaging resolution, the dataset posed significant challenges. Chandra noticed some pockets of contrast with only a few X-ray photons. And the variance in X-ray production in a given plane was usually tens of percent or so. To avoid inadvertently counting randomness as true variability, Meyer collaborated with statisticians at the University of Toronto and Imperial College London.

“It was almost a miracle to pull this result out of the data, because the observations weren’t designed to detect it,” says Meyer. The team’s analysis indicates that between 30 and 100 percent of the aircraft in the study showed variability over short time scales. “While we would like better constraints, the variance is not significantly zero,” she says.

The new findings poke holes in one of the main theories of X-ray production in black hole jets, and Meyer hopes the paper will spur future work. “We hope this is a real call for theorists,” she says, “to essentially look at this result and come up with aircraft models that are consistent with what we’ve come up with.”