For years, scientists have seen that the Milky Way apparently contained a huge cloud of antimatter near its center. But they haven't known why.
Antimatter, a staple of both science fiction and hard-science particle physics laboratories, is essentially subatomic particles that have the same mass, but different electrical charges than their ordinary counterparts such as electrons and protons. When a positron encounters its regular opposite, an electron, both are destroyed in a shower of new particles.
This is a useful feature in physics labs studying the basic fabric of the universe. But since the 1970s, scientists have scratched their head, wondering how antimatter is created in nature (as well as why the Big Bang apparently created more matter than antimatter – but that's a different question, for later).
Some researchers had thought that exploding stars might create the antimatter. Others, looking at the apparent shape of the cloud in the
Milky Way's central region, believed that it could be mysterious (and still speculative) dark matter decaying into pairs of electrons and positrons, which then destroyed each other, creating the gamma rays that researchers use to detect the presence of antimatter in the first place.
But now new observations by researchers using the European Space
Agency's Integral gamma-ray observatory point in a new direction. The observations show that the shape of the antimatter cloud, as deduced by the gamma rays reaching our corner of the galaxy, is in fact more lopsided than previously believed.
That means it doesn't fit the shape of the presumed dark matter distribution at the galaxy's core. But it does fit the distribution of a population of binary star systems, in which ordinary stars are being consumed by a nearby collapsed star, in the form of a neutron star or black hole.
That cannibalistic process is very likely responsible for the creation of the antimatter, researchers now say. As gas is ripped off the normal stars by their hungry partners, it spirals down towards the neutron star or black hole, and is heated enough to spontaneously produce electron-positron pairs in the resulting radioactive field.
Those pairs destroy each other, and a bit later, we see the resulting gamma rays here. Many scientists like this idea, because it doesn't force them to rely on the still-theoretical dark matter as an explanation.
"The link between (the binary star systems) and the antimatter is not yet proven but it is a consistent story," said Georg Weidenspointner, a researcher at the Max Planck Institute for Extraterrestrial Physics involved with the research.
Integral discovers the galaxy’s antimatter cloud is lopsided [ESA press release]
Source of Mysterious Antimatter Found [Space.com]
(Image: Artist's impression of the ESA's Integral observatory)
