Milky Way's "dark matter" mystery solved by astrophysicists

Washington, July 9 (ANI): A team of astrophysicists has solved a mystery that led some scientists to speculate that the distribution of certain gamma rays in our Milky Way galaxy was evidence of a form of undetectable "dark matter" believed to make up much of the mass of the universe.

In two separate scientific papers, the astrophysicists show that this distribution of gamma rays can be explained by the way "antimatter positrons" from the radioactive decay of elements, created by massive star explosions in the galaxy, propagate through the galaxy.

Thus, the scientists said, the observed distribution of gamma rays is not evidence for dark matter.

"There is no great mystery," said Richard Lingenfelter, a research scientist at UC San Diego's Center for Astrophysics and Space Sciences who conducted the studies with Richard Rothschild, a research scientist also at UCSD, and James Higdon, a physics professor at the Claremont Colleges.

"The observed distribution of gamma rays is in fact quite consistent with the standard picture," he added.

Over the past five years, gamma ray measurements from the European satellite INTEGRAL have perplexed astronomers, leading some to argue that a "great mystery" existed because the distribution of these gamma rays across different parts of the Milky Way galaxy was not as expected.

To explain the source of this mystery, some astronomers had hypothesized the existence of various forms of dark matter, which astronomers suspect exists, but have not yet found.

What is known for certain is that our galaxy and others are filled with tiny subatomic particles known as positrons, the antimatter counterpart of typical, everyday electrons.

The scientists calculated that most of the gamma rays should be concentrated in the inner regions of the galaxy, just as was observed by the satellite data.

"The observed distribution of gamma rays is consistent with the standard picture where the source of positrons is the radioactive decay of isotopes of nickel, titanium and aluminum produced in supernova explosions of stars more massive than the Sun," said Rothschild.

The scientists point out that a basic assumption of one of the more exotic explanations for the purported mystery - dark matter decays or annihilations - is flawed, because it assumes that the positrons annihilate very close to the exploding stars from which they originated.

"We clearly demonstrated this was not the case, and that the distribution of the gamma rays observed by the gamma ray satellite was not a detection or indication of a 'dark matter signal'," said Lingenfelter. (ANI)