Black holes snacking on small stars create particle accelerators that bombard Earth with cosmic rays

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Gamma rays detected by NASA's Fermi spacecraft indicate that microquasars are powered by small black holes slowly devouring stars. They pack quite a punch, bombarding Earth with cosmic rays.

Black holes snacking on small stars create particle accelerators that bombard Earth with cosmic rays : Read more

 

[Torbjorn Larsson]

This could be one type of cosmic ray source. Another proposed source could dominate the cosmic rays, at least at high energies, fulfilling observed spectral and flux conditions:

Physicists have struggled for decades to explain how and where the particles acquire such stupendous energy, invoking, for example, supermassive black holes at the cores of galaxies. But one theorist now argues that a subtle similarity among the highest energy rays points to a more modest source: the mergers of neutron stars. Proposed in a paper in press at Physical Review Letters, the idea has piqued the interest of astrophysicists, who now aim to test it.

“I totally agree that a neutron star merger is a promising candidate,” says Toshihiro Fujii, a particle astrophysicist at Osaka Metropolitan University who works with the Telescope Array, a huge cosmic ray detector in Dugway, Utah. Markus Roth, a particle astrophysicist at the Karlsruhe Institute of Technology who works on the Pierre Auger Observatory, an even bigger detector in Argentina, says, “I do not see any argument that would contradict [the] proposal.”

Neutron star pairs seem common enough to produce the right flux of ultra–high energy rays, Farrar says. They also might neatly explain the highest energy events, which are particularly mysterious. Theorists assume they are iron nuclei, but the usual candidates for the cosmic accelerator would struggle to accelerate iron to such high energies. Neutron star mergers, however, are factories of rare, heavier, more highly charged nuclei such a tellurium. So the highest energy cosmic rays could merely be some of those nuclei accelerated to the same rigidity as lighter nuclei. The scenario “just automatically explains this handful of ultra, ultra–high energy events,” Farrar says. “It’s so nice when it just falls out like that.”

https://www.science.org/content/art...etic-cosmic-rays-come-colliding-neutron-stars