The Black Hole in the Center of the Milky Way Is an Accelerator of Gamma Rays

Astronomers have found that the supermassive black hole located in the center of the Milky Way generates the mysterious gamma-ray emission detected in the center of our galaxy.

The mobile magnetic fields around the hole produce high-speed collisions that emit the gamma rays.

Extremely powerful gamma rays, with charges in the tens of tera-electronvolts (1 TeV means 1012 eV) have been picked up recently by ground-based gamma-ray observatories.

Some researchers have proposed them as the result of dark matter particles decaying, but not everybody agrees with this explanation.

The new research comes with the idea that the gamma rays are expelled by the most powerful naturally occurring particle accelerator, better than the best atom smashers used by researchers on Earth. The team made calculations based on the particle accelerator scenario, in which protons around the supermassive black hole are constantly hit by the hole's magnetic fields. These magnetic interactions speed up the protons so much that they are thrown into surrounding gas clouds.

The hole's magnetic field extends even farther away, so it keeps on kicking the protons to even increased speeds as they travel outwards. "Some of the protons could reach energies of 1000 TeV this way," said team member Fulvio Melia of the University of Arizona, in Tucson, US.

The scenario can match the brightness, spatial distribution, and proportion of different energies of gamma rays seen in the galaxy's center. Previous ideas of the decaying dark matter particles producing the gamma rays cannot be rejected, but none of them were clearly demostrated. "It's much more natural to think of the gamma rays as coming from the black hole, since the gamma rays are coming from a very compact region centred on the black hole itself", said Melia. "It seems like a very plausible scenario," says gamma-ray researcher David Kieda of the University of Utah in Salt Lake City, US, who was not a member of Ballantyne's team.

"In addition to explaining the bright, compact gamma-ray source around the supermassive black hole, the particle accelerator idea also accounts for a fainter, more spread out gamma-ray glow from the surroundings," he says. "But the glow would occur naturally in the particle acceleration scenario because some of the protons would make it a considerable distance from the black hole before colliding with gas particles and producing gamma rays," he says.

Photo credit: NASA