Stellar explosions puff up giant gamma-ray bubbles ⚡ экспресс
Using magnetohydrodynamic simulations with cosmological initial conditions and dynamic transport of multiple species of cosmic rays in the MeV–TeV range, the formation of bilobed gamma-ray outflows, analogous to the Fermi bubbles, has been reproduced for the first time without an active galactic nucleus — only through star formation and supernovae. The modeling included gamma-ray emission from neutral pion decay, relativistic bremsstrahlung, and inverse Compton scattering. In all three simulated galaxies with a Milky Way mass, such outflows are present, with their amplitude, shape, and spectrum fluctuating over time, alternating between lepton- and hadron-dominated phases. It is found that spectra where the inverse Compton flux exceeds the pion-decay contribution by an O(1) factor agree well with Fermi-LAT measurements. The simulations also predict synchrotron radio and soft X-ray radiation, revealing new observational signatures that connect the circumgalactic medium to cosmic-ray physics and the activity of the galactic center.
At the center of the Milky Way, a giant stellar cauldron boils. Massive stars are born and die there: each death is a supernova explosion, hurling clouds of charged particles into space. These particles, accelerated to nearly the speed of light, collide with gas and radiation, emitting gamma-ray light—the most energetic in nature. Thus, above the plane of the galaxy, two bubbles tens of thousands of light-years tall are puffed up—like steam bubbles above boiling water. The Fermi telescope spotted them back in 2010, but only now has a computer model shown that the black hole has nothing to do with it. The vigorous life of ordinary stars is enough. Moreover, different parts of the bubbles glow in their own way—it depends on how particles lose energy. This gamma-ray “rainbow” is called a spectrum. The biggest surprise: the bubbles are not hot gas, but the glow of particles accelerated to nearly light speed. And the simulation also predicted: wherever there is gamma-ray glow, there should be radio waves and X-rays as well. Now astronomers know where to point their telescopes.
🎯 Contrary to intuition, the bubbles’ light isn’t born from heat, but from particles flying almost at light speed.