No one who even remotely understands science will claim that we have a “good” understanding of dark matter. Even the name betrays how little we know about it. However, a new analysis using the aging Hubble Space Telescope suggests that we know even less than we thought. The Hubble analysis of dark matter shows more of it in places where we did not expect, by doing things that we did not expect either.
Dark matter is difficult to study because it does not produce, absorb, or reflect electromagnetic radiation. After all, it is invisible to us. However, we can deduce the presence of dark matter based on its gravitational effects, and so the team led by Massimo Meneghetti of the National Institute of Astrophysics in Italy analyzed dark matter in 11 large galaxy clusters.
Scientists believe that dark matter can account for most or all of the universe’s “lack of mass.” It accounts for perhaps as much as 85 percent of the universe, and we can not see any of it. If we ever want to understand dark matter, we need to start somewhere. Gravity lenses are as good a place as anywhere – scientists have been able to estimate the amount of dark matter in an area of space by comparing the predicted gravity from visible matter with the actual observed gravity. Even light cannot avoid gravity, so areas heavy with dark matter show gravity as light bends around them.
Meneghetti says galaxy clusters are the ideal place to study dark matter. The team generated simulations of the expected lens effects in the laboratory and then compared it to reality via Hubble. On a large scale, the models are accurate – the team then lens around the cluster as predicted. However, the study also revealed lenses around individual galaxies that were not predicted in the model. This may mean that the amount of dark matter in these galaxies could be much higher than assumed, 10 times or more.
To confirm these findings, the team conducted spectroscopic observations of the suspected galaxies. Visible light shifts allowed scientists to calculate the velocity of star circles, which is one of the few ways we can measure dark matter. This analysis confirmed that there was much more dark matter than current models predict.
We do not know what this means yet, but any discrepancy between models and reality is an opportunity to improve the models. It can help us figure out what dark matter is.