MIT scientists say a mysterious burst of light at the center of our galaxy might be caused by dark matter after all, four years after previous research concluded the light was caused by stars, not dark matter.
In the center of the Milky Way, there is a surplus of energy in the form of gamma rays that appears as a bright light. This excess energy is found throughout the Milky Way, but the cause of this particular surplus has been a source of debate in the scientific community since it was discovered 10 years ago, Massachusetts Institute of Technology postdoctoral researcher Rebecca Leane said.
In 2015, MIT physics professor Tracy Slatyer was among a group of researchers who discovered what was thought to be proof that the energy was caused by neutron stars. Now, a new study, led by Leane and coauthored by Slatyer, has reopened the debate.
A paper on the new research was published Tuesday in the journal Physical Review Letters.
In 2015, researchers from MIT and Princeton analyzed observations taken by the Fermi Gamma-ray Space Telescope of the energy at the galactic center. They determined that it was caused by high-energy, rapidly rotating neutron stars known as pulsars.
Because pulsars are individual balls of light, or point sources, the energy that a group of them emits presents as “clumpy,“ Leane said. Dark matter, on the other hand, would appear as a smooth cloud of energy. The 2015 research team found the energy source presented as clumpy, not smooth, and the scientific community accepted that the energy couldn’t be caused by dark matter, Leane said.
Dark matter is invisible matter that astronomers can’t detect, according to NASA. Scientists have not determined what dark matter could be, but they know that it does not emit light.
“Dark matter is some other type of matter that is not a visible matter,” Leane said. “Everything that you can see, everything that you can feel, only makes up about 5 percent of the universe. Part of the rest of this is dark matter.”
Scientists theorize dark matter could create energy surpluses through a process called “annihilation,“ in which dark matter particles that are close together destroy each other, leaving gamma rays in their wake, said Dan Hooper, head of the Fermilab Theoretical Astrophysics Group in Illinois and a physicist studying dark matter who was not involved in the study.
“Prior to 2015, the community was very excited about this signal, and many people were writing papers about the implications,“ Hooper said, adding that after the 2015 study came out, it “seemed to take the wind out of the sails of the dark matter idea, [and] for a number of years the interest in that subsided quite a bit.“
In the new study, Leane said she discovered a loophole in the model that was used in the 2015 research. By running a simulated dark matter signal through the model, Leane found that the dark matter mimicked a clumpy signal.
“We discover striking behavior consistent with a mismodeling effect in the real Fermi data, finding that large artificial injected dark matter signals are completely misattributed to point sources,” the study said. “Consequently, we conclude that dark matter may provide a dominant contribution to the [galactic center energy] after all.”
Scientists don’t know much about dark matter, so opening the possibility that it could be causing the energy surplus is exciting, Leane said. It would allow astronomers to get a better look at dark matter, its properties, and what it’s made of.
Leane said the debate could reach its conclusion in a few years. In addition to gamma rays, neutron stars emit radio waves that scientists can pick up on. If scientists can detect enough of the radio waves, this would prove once and for all that neutron stars are the cause, she said.
Hooper said the new findings have caused an enthusiastic reaction from those who study dark matter, and that the community is once again viewing the galactic center “in a newly reinvigorated“ way.