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Milky Way's Black Hole a Gamma Source?
eldavojohn writes "A paper recently accepted for publication (preprint here) proposes a sound explanation for the source of the gamma rays that permeate our galaxy. The Milky Way's central object Sagittarius A*, widely believed to be a supermassive black hole, is now suspected to be the source. To test this theory, two scientists created a computer model to track the protons, flung outward with energies up to 100 TeV by the intense magnetic fields near the event horizon, as they make a random walk through the plasma environment. It can take thousands of years for them to travel 10 light-years from the black hole, where they collide with lower-energy protons to form pions. These decay into gamma radiation emanating from a torus-shaped region around the central object."
There are already dangerous levels of radiation within our own solar system, however, we are protected by an atmosphere. I would imagine one of two possibilities. Any planet with the potential for life closer to the center of our galaxy would have enough shielding of some sort (either a thick atmosphere or a thick ocean) to allow life to form on almost any suitable location in the galaxy. The other possibility is, life can exist in high amounts of radiation, but it might not be life as we know it.
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The summary makes it sound as though this is an explanation for the DIFFUSE gamma-ray emission seen in our Galaxy. This is not the case, the paper only discuss a source of gamma-rays observed to be spatially coincident with the Galactic center. Gamma-ray telescopes do not have high angular resolution so there is a possibility that the gamma-rays are not actually coming from the Galactic center in the first place. Finally this is not a new proposal. Proton acceleration near black holes is quite commonly discussed and accepted. Furthermore photo-pion production is a well known process that has been well measured in the lab. I think the real meat of this paper is that they are suggesting observations of emission associated with the black hole that we have observed gravitationally for a while now. This is the big news, not that the gamma-rays in our galaxy have been explained, not that protons make pions which decay into gamma-rays.
Actually, other parts of the galaxy are farther from the milky way and other black holes. These arms, teeming with life, use gamma rays to communicate and travel. They haven't come calling since our arm is poisoned with radiation, making interstellar travel prohibitively dangerous!