ENGINEERINGNET.BE – The center of our galaxy blows out two colossal bubbles of gamma rays, spanning an impressive 50,000 light-years. Although it was discovered a decade ago with the Fermi Gamma-ray Space Telescope, the source of this hourglass-shaped phenomenon remains unclear.
These Fermi bubbles contain a number of puzzling substructures of very bright gamma rays. One of the brightest spots, the so-called Fermi cocoon, located in the southern lobe, was originally thought to be caused by past eruptions of the Milky Way’s supermassive black hole.
An international research team has now analyzed data from the GAIA and Fermi space telescopes to show that the Fermi cocoon is actually a result of emissions from the Sagitarius dwarf galaxy.
Due to the narrow orbit around our galaxy and the previous passes through its disk, the dwarf galaxy has lost most of its interstellar gas, and many of the stars have been ripped from its core and now sit in elongated ribbons.
Given that the Sagittarius dwarf is now completely silent – the galaxy contains neither gas nor nurseries for new stars – there are only a few possible explanations for these gamma rays, including a population of unknown millisecond pulsars or the annihilation of dark matter. .
Millisecond pulsars are remnants of a particular type of stars, significantly more massive than the Sun, that reside in narrow binary star systems and that erupted cosmic particles due to their extreme rotational energy.
The electrons that fire the millisecond pulsars collide with low-energy photons from the cosmic microwave background, which in turn are accelerated to high-energy gamma rays.
The researchers have convincingly demonstrated that the ‘cocoon’ of gamma rays is explained by millisecond pulsars in the Sagittarius dwarf, and that the hypothetical dark matter explanation is highly unlikely.
The discovery sheds light on millisecond pulsars as efficient accelerators of high-energy electrons and positrons. The results also suggest that similar physical processes may be underway in other dwarf satellite galaxies of the Milky Way.