Milky Way’s black hole may be spewing out cosmic rays

Science ^ | 16 Mar, 2016 | Daniel Clery

[MtnClimber]

Mysterious high-energy particles known as cosmic rays zip through space at a wide range of energies, some millions of times greater than those produced in the world’s most powerful atom smasher. Scientists have long thought cosmic rays from inside our galaxy come from supernova explosions, but a new study has fingered a second source: the supermassive black hole at the heart of the Milky Way. With this new result, the search for cosmic ray origins, which has frustrated scientists for more than 100 years, has taken an unexpected new twist.

“It’s very exciting,” says astrophysicist Andrew Taylor of the Dublin Institute for Advanced Studies. “This has probably shaken the field quite a lot. People will need to reassess their models.”

Cosmic rays pose a mystery for astronomers because they don’t follow a straight path through space. They get tugged and pushed by magnetic fields, so it is almost impossible to figure out where particular particles have come from. So instead, researchers have looked at gamma rays, high-energy photons that are thought to be produced at or near the source of the cosmic rays. Find out where the gamma rays come from, and you’ve probably found the source of cosmic rays.

Although many of the cosmic rays from within our galaxy appear to be blasted out from supernova explosions at blistering speeds, such explosions can’t explain the highest energy cosmic rays: those with energies measured in peta-electronvolts (PeV, or 1015 eV). (Here on Earth, 1 PeV is the total energy that the Large Hadron Collider can achieve when slamming together lead ions.)

“We don’t really know what’s going on,” says Werner Hofmann of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany.

The difficulty in studying both cosmic rays and their accompanying gamma rays, however, is that they get destroyed by colliding with atoms high in the atmosphere and never reach Earth’s surface. These collisions do, however, send showers of other particles raining down toward the surface. Astronomers can measure the spread of those particles with detectors on the ground, or capture flashes of light called Cherenkov radiation, which the particles give off as they decelerate in the atmosphere.

[Bullish]

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they’ll shut it down