The search for dark matter continues, in part through China's Dark Matter Particle Explorer (DAMPE) – and the probe just picked up a suggestion of something on its instruments that suggests we could be getting closer to the big discovery.
No, we haven't found dark matter yet, but we have found what could be an indicator of it, leading us closer to this mysterious stuff that's believed to make up most of the Universe.
What the team led by the Chinese Academy of Sciences found is an intriguing anomaly in DAMPE's readings of over 1.5 million cosmic ray electrons and positrons, captured in unprecedented high resolution and with minimal background noise.
"It may be evidence of dark matter," one of the team, astrophysicist Chang Jin, told Dennis Normile at Science, while also admitting the same anomaly could be caused by some other source of cosmic ray energy.
Electrons represent the matter that everything we can see is made of, with positrons the antimatter counterparts.
By measuring their energy, scientists hope to spot an excess that could be produced by weakly interacting massive particles (WIMPs) breaking down, one of the hypothetical signs of dark matter.
The spectral break. (Chinese Academy of Sciences)
When the number of these particles is plotted against their energy, a smooth curve should be created – but DAMPE has spotted a break in this shape.
Technically, it's called a spectral break, and while we've seen indirect measurements of it before, this is the first time such a blip has been directly spotted.
The readings suggest that something else is out there interfering with these energy signals: the decay of dark matter, perhaps.
As is often the case though, scientists are going to need a whole lot more data to be sure.
Fortunately, DAMPE should keep working for another five years or so, and another 10 billion cosmic ray readings, so we'll get chance to dig deeper into this strange blip in the energy curves.
Scientists still aren't sure exactly what dark matter is – another question DAMPE might help answer – but from our observations of gravity, the matter in the Universe, and the way light bends through space, most experts agree there is something else out there for the laws of physics to work.
However, being able to spot it directly is proving incredibly difficult. As well as DAMPE in space, the XENON1T detector deep underground in Italy is tasked with trying to spot the faint ripples of dark matter.
Like DAMPE, XENON1T is looking for those elusive WIMPs – which in true dark matter form, we don't know much about.
The hope is that by definitively measuring dark matter's impact on actual matter, as in rays of colliding electrons and positrons across space, we can finally observe it ourselves.
"Together with data from the cosmic microwave background experiments, high energy gamma-ray measurements, and other astronomical telescopes, the DAMPE data may help to ultimately clarify the connection between the positron anomaly and the annihilation or decay of particle dark matter," says one of the researchers, Fan Yi-Zhong.
The findings have been published in Nature.