Contrary to what previous studies have suggested, new research indicates that gamma ray bursts coming from the center of the galaxy are unlikely to be from dark matter, and instead originate from a different kind of astrophysical phenomena, possibly rapidly rotating neutron stars.
Past research suggested that the gamma rays coming from the dense region of space in the inner part of the Milky Way might have been created by collisions involving dark matter particles, but studies conducted by two separate teams have found that the signals given off by the gamma rays are not characteristic of those expected from dark matter.
The two groups, one a joint team from Princeton University and the Massachusetts Institute of Technology (MIT) and the other comprised of scientists from the Netherlands, both reported this week in the journal Physical Review Letters that the rays likely came from a different source, and that the fast-rotating stars known as millisecond pulsars were the best candidates.
“Our analysis suggests that what we are seeing is evidence for a new astrophysical source of gamma rays at the center of the galaxy,” Mariangela Lisanti, an assistant professor of physics at Princeton and co-author of one of the studies, said in a statement. “This is a very complicated region of the sky and there are other astrophysical signals that could be confused with dark matter signals.”
Distribution of high-energy particles suggests a different source
Although both teams reached the same conclusion, they used different techniques to arrive there. The US group used image-processing techniques to examine how the gamma rays should appear if they were coming from the collision of a hypothesized type of dark matter particles known as weakly interacting massive particles (WIMPs).
Lisanti and her colleagues analyzed images of gamma rays captured using NASA’s Fermi space telescope, using a method of statistical analysis to test a widely-accepted dark matter model that suggests that the collision of two WIMPs causes them to annihilate each other, producing gamma rays – the highest energy form of light in the universe – in the process.
This model suggests that these high-energy particles, also known as photons, should be evenly distributed among the pixels in images captured by the Fermi telescope, according to the study authors. However, their analysis revealed that the photons were actually distributed in isolated pixels, meaning that the gamma rays probably originated from a different source.
The Dutch team reached largely the same conclusion using a method centered around wavelet transformation, and while the researchers are not 100 percent certain what that alternate source might be, they suspect that it could be millisecond pulsars. While the researchers note that their findings are a bit of a setback in the hunt for dark matter, the results are nonetheless intriguing.
Christoph Weniger, a researcher at the University of Amsterdam and the lead author of the Netherlands-based team, called the discovery a win-win, adding, “Either we find hundreds or thousands of millisecond pulsars in the upcoming decade, shedding light on the history of the Milky Way, or we find nothing. In the latter case, a dark matter explanation for the gamma ray excess will become much more obvious.”
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Feature Image: Studies by two independent groups from the US and the Netherlands indicate that the observed excess of gamma rays from the inner galaxy likely comes from a new source rather than from dark matter. The best candidates are rapidly rotating neutron stars, which will be prime targets for future searches. The Princeton/MIT group and the Netherlands-based group used two different techniques, non-Poissonian noise and wavelet transformation, respectively, to independently determine that the gamma ray signals were not due to dark matter annihilation. (Credit: Image courtesy of Christoph Weniger)
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