Our universe consists of matter, not antimatter. But it also contains antiparticles – only science has not been able to find their source yet
After all what we know today, matter and antimatter are physically completely equivalent. Whether an atom is built of positron and antiproton or of electron and proton should not interest nature. And yet our universe is not half antimatter – there must have been a point in its development where one form was preferred over the other.
However, this does not mean that antimatter exists only in science fiction (who remembers the positronics of the Perry Rhodan books)?) or in the laboratory gabe. The presence of anti-electrons was shown already three years ago for the first time – on the basis of the typical gamma-emission lines with an energy of 511 keV, which reveal that here an electron got in the way of a positron (or vice versa). But how these positrons were created has been a mystery to science until now.
The map above shows the whole sky in the light of the 511 keV radiation; in the center the center of the Milky Way. The radiation from the western galactic disk is clearly brighter than that from the eastern galactic disk. A very similar picture is given by the distribution of the low-mass Rontgen double stars (below). Pure coincidence? (Graphic: Weidenspointner et al. / Nature)
At least there were some candidates. Candidate number 1: When a star ends its life in a supernova, it also produces heavy radioactive isotopes that emit positrons as they decay. Among them, on the one hand, Cobalt 56 – here scientists doubt that the positrons created during the decay have enough energy to leave the supernova and then annihilate with electrons. Among them is aluminum 26, which, according to current calculations, could actually be responsible for a quarter of the positrons. So there still remains the question about the rest.
As an answer here the dark matter offers itself – this is obviously always gladly brought into the field, if otherwise no answer is found. According to this theory, the positrons in question were created during the decay of components of this dark matter (see "Where have the baryons gone"). The fact that these are supposed to be arranged in the form of a halo around the galaxy, became the theory additionally truncated.
In case of doubt, however, science always prefers an answer that makes do with known matter. In the suspicion were also already double star systems from a star in sun size and a compact stellar object, speak a neutron star or even a black hole. In such systems, the compact object sucks gas from its companion – with such a strong gravitational pull that the gas gains a lot of energy and emits rontgen radiation. It can become again so coarse that in the consequence from two radiation "particles" an electron-positron pair can develop.
The mechanism is really not new. What is new, however, is that scientists have compared the distribution of such binary star systems with the distribution of gamma rays characteristic of positron annihilation. The researchers have published the result in the current ie of the scientific journal Nature. And it certainly did not stop there, if a consensus had not been found. To this end, researchers analyzed four years of spectroscopic data collected by ESA’s Integral satellite. If the match is more than a coincidence, then more than half of the positrons detected in space should come from such binary systems. For the rest then supernovae or a similar process at the gigantic black hole in the center of the galaxy were responsible. However, the researchers admit that too little is known about the population of the Rontgen binary systems.