ENGINEERINGNET.BE – The center of our galaxy is blowing out two massive gamma-ray bubbles spanning an impressive 50,000 light-years. Although it was discovered a decade ago using the Fermi Gamma Ray Space Telescope, the source of this hourglass-shaped phenomenon remains unclear.
Fermi bubbles contain a number of perplexing structures of extremely bright gamma rays. One of the brightest spots, called the Fermi cocoon, located in the southern lobe was originally thought to be caused by previous 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 in fact the result of emission from the Sagitarius dwarf galaxy.
Because of the narrow orbit around our galaxy and past passes through its disk, the dwarf galaxy has lost most of its interstellar gas, many stars have been yanked out of its core and are now in long ribbons.
Given that the Sagittarius dwarf is now completely silent—the galaxy contains no gas and no nurseries of new stars—there are only a few possible explanations for gamma rays, including a cluster of millisecond pulsars or dark matter annihilation.
Millisecond pulsars are the remnants of a particular type of star, much larger than the Sun, that reside in narrow binary star systems that erupted cosmic particles due to their intense rotational energy.
The electrons firing millisecond pulsars collide with low-energy photons from the cosmic microwave background, which in turn are accelerated into high-energy gamma rays.
The researchers convincingly demonstrated that the gamma-ray “cocoon” can be explained by millisecond pulsars in the Sagittarius dwarf, and that the hypothetical explanation for dark matter is highly unlikely.
This discovery highlights millisecond pulsars as efficient accelerators of high-energy electrons and positrons. The results also suggest that similar physical processes may be underway in other Milky Way dwarf galaxies.
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