Astronomers discovered only relatively recently that black hole jets emit X-rays, and how the jets accelerate particles to this high-energy state is a mystery. One leading model of how such jets generate X-rays expects the jets’ X-ray emissions to remain stable over long time scales (millions of years). However, University of Maryland astronomer Eileen Meyer and colleagues found that the X-ray emissions of a statistically significant number of jets varied over just a few years.
“One of the reasons we’re excited about the variability is that there are two main models for how X-rays are produced in these jets, and they’re completely different,” said Dr. Meyer, lead author of the study published in the journal Nature Astronomy.
“One model invokes very low-energy electrons and one has very high-energy electrons. And one of those models is completely incompatible with any kind of variability.”
For the study, Dr. Meyer and co-authors analyzed archival data from NASA’s Chandra X-ray Observatory.
They looked at nearly all of the black hole jets for which Chandra had multiple observations, which amounted to 155 unique regions within 53 jets.
“Discovering relatively frequent variability on such short time scales is revolutionary in the context of these jets, because that was not expected at all,” Dr. Meyer said.
In addition to assuming stability in X-ray emissions over time, the simplest theory for how jets generate X-rays assumes particle acceleration occurs at the center of the galaxy in the black hole ‘engine’ that drives the jet.
However, the authors found rapid changes in X-ray emissions all along the length of the jets. That suggests particle acceleration is occurring all along the jet, at vast distances from the jet’s origin at the black hole.
“There are theories out there for how this could work, but a lot of what we’ve been working with is now clearly incompatible with our observations,” Dr. Meyer said.
Interestingly, the…
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