Cosmic Accelerators: Unlocking the Secrets of Microquasar GRS 1915+105

In this episode, we dive into the extreme and fascinating world of microquasars—binary systems where a compact object, like a black hole, feeds off a companion star and launches powerful, relativistic jets. Our spotlight is on GRS 1915+105, one of the most dynamic and powerful microquasars known in the Milky Way.

Recent groundbreaking observations from the LHAASO and Fermi-LAT observatories have mapped broadband gamma-ray emissions from this system, revealing that it operates as an extreme "PeVatron"—an accelerator capable of pushing particles to multi-PeV (peta-electron volt) energies. We break down the evidence pointing to a "hadronic scenario," which suggests that these mind-boggling energies are produced when highly accelerated protons from the jet smash into the dense ambient gas surrounding the system.

Join us as we discuss how this discovery proves that microquasars are exceptionally efficient particle accelerators and how they might be the missing link to understanding the origins of the most energetic cosmic rays in our galaxy.

Key Takeaways:

• What is a Microquasar? A look at the anatomy of GRS 1915+105, a system featuring a black hole pulling material from a small K-type star and firing off jets at 80% the speed of light.
• The Power of LHAASO & Fermi-LAT: How a joint analysis of 4 years of LHAASO data and 17 years of Fermi-LAT data finally detected persistent gamma-ray emissions from this source.
• The Hadronic Accelerator: Why the shifted centroid of the gamma-ray emission suggests that protons (rather than electrons) are being accelerated by the jet's mechanical power and colliding with surrounding interstellar gas.
• Solving a Galactic Mystery: How just a handful of microquasars like GRS 1915+105 could be responsible for supplying the entire Milky Way with PeV-level cosmic rays.

Reference:

Cao, Z., Aharonian, F., Bai, Y.X., et al. (The LHAASO Collaboration). "Extreme PeV accelerator associated with GRS 1915+105." (Preprint: 2606.25054v1).

Acknowledements: Podcast prepared with Google/NotebookLM. Illustration credits: NASA/CXC/A.Hobart