The spiral shape of a galaxy is an image that would be familiar to many of us but the story behind that shape is much less understood. We all know that gravity inexplicably pulls all matter together however if we were to weigh everything we could see it wouldn’t fully account for the resulting shapes and distributions we see throughout the universe. The missing mass is what is commonly referred to as Dark Matter, a theorized type of matter which is incredibly hard to detect directly yet must be pervasive throughout the universe due to its gravitational effects. However that might soon change if observations from our own parent star prove to be correct and we’ll be able to detect dark matter in our cosmic backyard.
The picture above is what’s known as the Bullet Cluster, the collision of 2 galaxy clusters with each other which is thought to provide some of the best evidence for dark matter. It’s theorized that in a collision of this nature the dark matter would avoid interaction with all the normal matter and would essentially race ahead. This theory is supported by the gravitational lensing observed between the two galaxies as without some form of dark matter the lensing would follow the matter consistently whereas here it appears to be ahead of its observable matter brethren. There’s still not enough evidence here to call it a direct detection of it, especially when other modified standard models can accommodate the effect readily enough.
However physicists at the University of Leicester in the UK have detected what could be the decay of dark matter particles coming from our sun which, if proven to be correct, would be the first direct detection of dark matter. The theory goes that axions, particles which were theorized to solve one of the more puzzling problems in quantum chromodynamics and are theorized to be a component of cold dark matter, are created in the sun and make their way to earth. Much like neutrinos they don’t interact with matter very often and thus race from the core at light speed, unimpeded by the sun’s great mass. When they reach our magnetic field however they decay into a x-ray photon which means that the level of background x-rays should be higher within the earth’s magnetic field. This is what the researchers have found and data from other orbital observatories seems to corroborate this.
Of course the theory is not without its problems, notably that the properties of the axion that they’re theorizing would be different to the one that’s predicted by the current model. There’s evidence to suggest this from other observations so in order to prove the theory one way or the other further analysis with that additional data will have to be taken into consideration. It’ll likely be years before we’ll have a definitive answer on this particular theory thanks to the large data sets that they’re working with but either result will provide some insight into where dark matter might be hiding.