The distribution of certain gamma-rays in the galaxy is peculiar

Jul 10, 2009 15:01 GMT  ·  By

Many astronomers have speculated that the peculiar distribution of certain forms of gamma-rays in our galaxy, the Milky Way, may be evidence to support the presence of some form of undetectable “dark matter,” which influences its spread patterns. But these theories are disproved by two new scientific papers, one of which appears in the July 10th issue of the journal Physical Review Letters. Experts confirm that the weird disposition is caused by the path that “antimatter positrons” take through the galaxy, as they are propelled at high speeds.

These positrons are generated when massive stars in the galaxy explode into supernovas, or collapse into black holes. The elements that are created during these times of cosmic unrest naturally decay at certain rates, which is the main production process for this peculiar type of particles. Additionally, the researchers say, this line of reasoning is not exactly the most intuitive one, but explaining a phenomenon by attributing it to something that no one has ever detected is not exactly good science. Dark matter may be the possible explanation for the framework in which galaxies interact, but it does not explain gamma-ray fluctuations in our own galaxy.

“There is no great mystery. The observed distribution of gamma rays is in fact quite consistent with the standard picture,” University of California in San Diego (UCSD) Center for Astrophysics and Space Sciences researcher Richard Lingenfelter explains. For the new studies, the expert cooperated with fellow UCSD research scientist Richard Rothschild, as well as with Claremont Colleges Physics Professor James Higdon. The largest part of the measurements that created the previous theories about the radiation distribution came over the past five years from the European satellite INTEGRAL.

“These positrons are born at nearly the speed of light, and travel thousands of light years before they slow down enough in dense clouds of gas to have a chance of joining with an electron to annihilate in a dance of death. Their slowing down occurs from the drag of other particles during their journey through space. Their journey is also impeded by the many fluctuations in the galactic magnetic field that scatter them back and forth as they move along. All of this must be taken into account in calculating the average distance the positrons would travel from their birthplaces in supernova explosions,” Higdon explains.

“Some positrons head towards the center of the Galaxy, some towards the outer reaches of the Milky Way known as the galactic halo, and some are caught in the spiral arms. While calculating this in detail is still far beyond the fastest supercomputers, we were able to use what we know about how electrons travel throughout the solar system and what can be inferred about their travel elsewhere to estimate how their anti-matter counterparts permeate the galaxy,” Rothschild adds.

“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,” he concludes.