Using an instrument on the International Space Station, astronomers have found the first evidence of dark matter — an elusive form of matter that is much more abundant than 'normal' matter, but cannot be directly seen by any of our telescopes or instruments.
Dark matter has been very hard to find so far, because it doesn't interact with light and it doesn't emit light. The only way that we can possibly detect its presence is due to the effect it has on the normal matter around it. If there is something made of dark matter that is big enough, its gravity will not only have an effect on the objects made of normal matter that are close by (causing them to move in specific ways), but it will also deform spacetime like normal matter does, and create a gravitational lensing effect that we can see. Since dark matter makes up 95% of the matter in the universe, with normal matter (us, the Earth, the planets, stars, etc) making up the other 5%, it's fairly important for us to figure out exactly what dark matter is if we're to get a good understanding of the universe.
This new instrument, known as the Alpha Magnetic Spectrometer (AMS), which is mounted on the exterior of the space station, has been watching the space around Earth for antimatter particles and cosmic ray particles for the past 18 months. In that time, the spectrometer has recorded around 25 billion particle interactions, and has found 400,000 'positrons' — the antimatter equivalent of the electron. The data collected comparing the number of positrons and their energies has matched what scientists have predicted they would see for positrons originating from the annihilation of dark matter.
"As the most precise measurement of the cosmic ray positron flux to date, these results show clearly the power and capabilities of the AMS detector," said AMS spokesperson, Samuel Ting, in a CERN press statement. "Over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter, or whether they have some other origin."
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One possibility is that these excess positrons were from a pulsar — the collapsed core of star that rotates rapidly while putting out powerful beams of radiation. If these positrons showed that they were coming from a specific direction, they would likely be due to a pulsar, but the positrons the AMS saw were coming from all directions evenly. It's still possible that they could be the result of many different pulsars throughout the galaxy, so the scientists aren't making any absolute conclusions just yet, but the results look very promising that these are, indeed, the result of dark matter annihilations.
(Photo courtesy: NASA)
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