Twenty Years of Watching One Galaxy, and It Made Less Sense

• Twenty years of observing the blazar PKS 2155-304 have revealed that the standard model of particle acceleration in its jets does not hold. The data shows no long-term correlation between optical and X-ray brightness, and the flares do not behave consistently over time. The team suggests that each outburst is driven by a different mechanism, and that the source of high-energy neutrinos is not a single process but something else.

• The study highlights the complexity of blazar physics, as the standard picture of electrons producing the observed radiation does not fit the data. The discovery of a statistically solid dip in the spectrum, occurring when the blazar was not flaring, suggests that hadronic processes—where protons rather than electrons are responsible for particle acceleration—are at play. This finding adds to the mystery of how high-energy neutrinos are produced and how they are linked to their sources.

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