In “Antimatter surplus is not dark matter’s smoking gun” (New Scientist, September 6, 2011), Stuart Clark explains,
Antimatter enthusiasts will love it; dark matter hunters not so much. NASA’s FERMI satellite has confirmed a previous hint that there is more antimatter than expected coming from space. The bad news is that the result almost certainly rules out dark matter as the source.
Antimatter is matter with the charges reversed – positrons (+), instead of electrons (-), for example. It is present today in small numbers. Dark matter is a theoretical concept: Matter that emits no light signal, hence the name. It may very well exist, but so far no such particle has been captured.
Dark-matter theorists had been expecting to find that the number of positrons would suddenly drop at some energy level. This cut-off would be the “smoking gun” of dark matter and would fix the mass of its particle – currently unknown – because the positrons could not be created with more energy than the dark-matter particle’s mass. However, FERMI shows no such cut-off, driving up the mass of a putative dark-matter particle into realms that make theoreticians uncomfortable.
Some folk experience vast relief, just knowing that there are realms that make theoreticians uncomfortable. That means they are not making stuff up wholesale. (Just retail?)
… the antimatter must be coming from as-yet unidentified celestial objects, but not dark matter: the intensely energetic environments of neutron stars have been suggested as a possible source. This conclusion does not mean, however, that dark matter does not exist – just that this particular signal has turned out to be a red herring rather than a smoking gun.
No one said dark matter didn’t exist. Whether it can gratify all agendas is quite a different question.
See also: Dark energy is real, say some