String theory is usually tested here on Earth. But the space observatory Chandra decided to show us all that it can be tested in even galaxy clusters deep in the Universe. But axions will not be happy with the results.
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Theory of Everything
One of the key ideas of current physics is that all known forces, particles and interactions can be connected through one all-encompassing theory – The Theory of Everything. Sadly, none such theory reigns at the moment but we do have some more or less hopeful candidates.
One of the best-known candidates is string theory. And there are several versions of this theory among scientists. Plus, there is a lot of speculation going around strings but were few of these speculations were experimentally tested so far. Recently, astronomers decided to use the x-ray observatory, Chandra, to do just that. And it seems that managed to get a lot done but one that will not make people who were rooting for axions happy.
X-Ray Destroyer of Axions
Chandra observed galaxies clusters and looked for evidence of the existence of a certain type of particles that are predicted by string theory. Until recently, x-ray astronomy did not seem like it could really help with string theory. But as the research lead – Christopher Reynolds from the University of Cambridge – says if they could detect these particles it could change physics as we know it.
Reynolds' team searched for axion particles. These are still theoretical particles that should have an incredibly low mass. The estimates range between roughly a millionth of the mass of an electron and no mass at all. A portion of scientists even thinks that axions could be the desperately searched for an explanation for dark matter – which as you might know fills the Universe but no one has ever seen it.
If ultralight axions exist then one of their incredible properties should be that sometimes they change into photons when they pass through a magnetic field. And the opposite should also be the case – under certain circumstance photons should change into axions. How often this would happen should depend on the convertibility of axions – just to make it “simpler”. And some scientists – apart from the existence of axions themselves – also say that a whole class of axion-like particles should exist that would have their own convertibilities while having the same mass.
Reynolds and his coworkers used galaxy clusters as a space experiment that runs incredibly far away fro us. Gigantic magnetic fields can be found inside of galaxy clusters and at the same time, we can find sources of x-ray radiation. If axions or axion-like particles are being converted into photons then we should be capable of detecting it.
The researchers and the Chandra observatory observed x-ray radiation that is being produced by matter falling into the mouth of the supermassive black hole in the center of the Perseus galaxy cluster for five days. Long term observation and the strong x-ray sources assured us that we should detect the conversion of axion and axion-like particles into photons.
Nonetheless, Reynolds and his colleagues did not detect anything. And this was the so far most detailed observation. Thanks to their results we can say that the majority of axion-like particles up to the tiniest of mas that is one-millionth of a billionth of the mass of an electron do not exist. But, as the researchers themselves say – that doesn't mean that axion-like particles or axions do not exist. But it definitely lowers their chances.
One possibility is that axions and axion-like particles have much lower convertibility then was the sensitivity of the experiment. Or, axion-like particles have a much higher mass then the experiment accounted for. Or, axions and axion-like particles just do not exist. Further research will tell us more.
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