Blazars: A laboratory for exploring modern physics

Blazar jets, originating very close to supermassive black holes, are modeled using special relativity, electricity, magnetism, and particle physics. Astronomers use the light emitted within blazar jets to understand the extremely energetic relativistic plasma that resides there. Students are often curious about these topics, and concrete examples of how they play out in nature can be helpful to motivate their learning of fundamental physics. Here, we give four examples of topics that are covered in a Modern Physics course, but they may also be interesting in the context of more advanced physics courses like Special Relativity and Particle Physics. First, we show how special relativity applies to large-scale blazar jets. Second, we show how synchrotron radiation within a highly collimated jet of tenuous plasma produces X-rays. These X-rays, originally discovered in quasar spectra, were the first hallmark of non-thermal acceleration. Third, we show how inverse-Compton scattering occurs and is observed as high-energy γ-rays by an astronomer. Finally, we show that pair production can occur when a high-energy γ-ray intercepts starlight on its way toward the astronomer and how the mean-free path of the γ-rays creates a TeV Cosmic Horizon. Example homework problems appropriate for a Modern Physics class are provided for instructors.