Cosmic Antimatter Hints at Origins of Huge Bubbles in Our Galaxy's Center

upstart writes:

The Fermi bubbles may have started life as jets of high-energy charged particles:

Bubbles of radiation billowing from the galactic center may have started as a stream of electrons and their antimatter counterparts, positrons, new observations suggest. An excess of positrons zipping past Earth suggests that the bubbles are the result of a burp from our galaxy's supermassive black hole after a meal millions of years ago.

For over a decade, scientists have known about bubbles of gas, or Fermi bubbles, extending above and below the Milky Way's center (SN: 11/9/10). Other observations have since spotted the bubbles in microwave radiation and X-rays (SN: 12/9/20). But astronomers still aren't quite sure how they formed.

A jet of high-energy electrons and positrons, emitted by the supermassive black hole in one big burst, could explain the bubbles' multi-wavelength light, physicist Ilias Cholis reported April 18 at the American Physical Society meeting.

In the initial burst, most of the particles would have been launched along jets aimed perpendicular to the galaxy's disk. As the particles interacted with other galactic matter, they would lose energy and cause the emission of different wavelengths of light.

Those jets would have been aimed away from Earth, so those particles can never be detected. But some of the particles could have escaped along the galactic disk, perpendicular to the bubbles, and end up passing Earth. "It could be that just now, some of those positrons are hitting us," says Cholis, of Oakland University in Rochester, Mich.

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