No one who even remotely understands science would argue that we have a “good” understanding of dark matter. Even the name betrays how little we know. However, a new analysis using the aging Hubble Space Telescope suggests we know even less than we thought. Hubble’s analysis of dark matter shows more in places we didn’t expect, doing things we didn’t expect.
Dark matter is difficult to study because it does not produce, absorb or reflect electromagnetic radiation. For all intents and purposes, it is invisible to us. However, we can deduce the presence of dark matter based on its gravitational effects, and this is how the team led by Massimo Meneghetti of the National Institute of Astrophysics in Italy analyzed dark matter in 11 large clusters of galaxies.
Scientists believe dark matter may explain most or all of the universe’s “missing mass”. It could represent a whopping 85 percent of the universe and we can’t see anything of it. If we ever want to understand dark matter, we have to start somewhere. The gravitational lens is as good a place as anywhere: Scientists were able to estimate the amount of dark matter in a region of space by comparing the predicted gravity of visible matter with the actual observed gravity. Light also cannot escape gravity, so areas filled with dark matter will exhibit gravitational lenses as light bends around them.
Meneghetti says galaxy clusters are the ideal place to study dark matter. The team generates simulations of the expected lens effects in the lab and then compares them to reality via Hubble. On a large scale, the models are accurate: the team saw the lenses around the cluster as expected. However, the study also revealed the lens around individual galaxies that wasn’t predicted in the model. This could mean that the amount of dark matter in those galaxies could be much higher than previously believed, by 10 times or more.
To confirm these results, the team conducted spectroscopic observations of the suspicious galaxies. The shifts in visible light have allowed scientists to calculate the speed of orbiting stars, 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 still don’t know what that means, but any discrepancy between models and reality is an opportunity to improve the models. This could help us understand what dark matter is.