Galactic cosmic ray model works without physics, and that is bad

Fermi gamma ray image of the huge bubbles originated at the center of the Milky Way. Follow-up radio and microwave observations revealed magnetic fields and ridgelike structures in these bubbles. (credit: NASA/DOE/Fermi LAT/D. Finkbeiner et al.)

Way back when the world was young and I still attended physics conferences, I got very excited by galactic cosmic rays. There seemed to be more cosmic rays than expected coming from the center of our galaxy. Those excess cosmic rays might be evidence for dark matter, which would be a big breakthrough if confirmed. Later modeling of cosmic ray sources showed that the extra cosmic rays were probably not coming from the annihilation of dark matter. But, now it seems we are back to square one, because that model may not have been accurate.

How’d they get here?

It is now reasonably certain that the cosmic rays that are observed to be coming from the center of the galaxy are more numerous than can be accounted for by known sources of cosmic rays. That doesn't mean too much because cosmic rays scatter, so we don’t see clear dots of cosmic ray sources in the galactic center. Instead, like looking at the Sun on a foggy day, there is a diffuse glow of cosmic rays with some brighter areas. To determine how that diffuse glow is constructed, scientists look at known sources of cosmic rays, like supernovae, and use these observations to estimate the total amount and energy of cosmic rays expected from the galactic center.

What we see, however, does not match this model. There were several issues. First, there are cosmic rays with energy far beyond what can be produced by supernovae. Unlike other very high-energy cosmic rays, these almost certainly originated inside our galaxy.