The Black Hole in the Middle of the Milky Way Is a High Energy Emitter

Astrophysicists consider the Milky Way as a relatively placid place of the Universe, yet they face a puzzle: the center of our galaxy is loaded with lethal gamma-rays, whose source has been unknown.

Now, a research team believes it has solved the mystery: the rays are emitted by the supermassive black hole situated at the galaxy's center. This black hole was discovered in 1998 and possesses the mass of roughly 2.6-million suns.

It spits out huge amounts of matter but was considered too weak and small, compared to the black holes from the center of other galaxies, to emit much radiation in the gamma-ray specter.

But in 2004, astronomers proved that indeed, the Milky Way black hole emitted gamma-rays, and now the new research led by David Ballantyne of the University of Arizona in Tucson points to magnetism as the mechanism.

The Milky Way's central black hole revealed to be strong enough to induce a powerful but chaotic magnetic field stretching over a distance of approximately 10 light-years.

The team calculated the hypothetical trajectories of some 220,000 protons, ejected from the black hole and how the magnetic field bounced them.

The theoretical results were compared with recent observations by ground-based instruments of the trajectories of the gamma-rays and 69% of the computer-generated trajectories fitted them. The gamma rays are thought to be the result of the collision of the protons with hydrogen atoms within huge gas clouds orbiting the black hole at 10 light-years out. "The findings could help astrophysicists understand how the most powerful black holes in the universe likewise produce gamma radiation. The same particle slinging almost certainly occurs in all black-hole systems," said co-researcher Fulvio Melia, also of the University of Arizona.

"The findings are interesting, but not necessarily conclusive," says astrophysicist Valerie Connaughton of NASA's Marshall Space Flight Center in Huntsville, Alabama.

"There could be an alternative explanation, such as a recent supernova in the vicinity of the galactic center, which could be accelerating the high-energy protons being detected. Further observations are needed, because we still don't really understand all of the physics involved."

Image credit: Sarah Ballantyne