No one who even remotely understands the science would contend 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 we know even less than we thought. The Hubble analysis of dark matter shows more of it in places where we didn’t expect, doing things we also didn’t expect.
Dark matter is difficult to study because it doesn’t produce, absorb, or reflect electromagnetic radiation. For all intents and purposes, it’s invisible to us. However, we can infer the presence of dark matter based on its gravitational effects, and that’s how the team led by Massimo Meneghetti of the National Institute for Astrophysics in Italy analyzed dark matter in 11 large galaxy clusters.
Scientists believe that dark matter may account for most or all of the universe’s “missing mass.” It may account for a whopping 85 percent of the universe, and we can’t see any of it. If we ever want to understand dark matter, we’ve got to start someplace. Gravitational lensing is as good a place as anywhere — scientists have been able to estimate the amount of dark matter in a region of space by comparing the predicted gravity from visible matter with the actual observed gravity. Even light cannot evade gravity, so areas heavy with dark matter will show gravitational lensing as light bends around them.
Meneghetti says galaxy clusters are the ideal place to study dark matter. The team generates simulations of the expected lensing effects in the lab, and then compared that with reality via Hubble. On the large scale, the models are accurate — the team saw lensing around the cluster as predicted. However, the study also revealed lensing around individual galaxies that wasn’t predicted in the model. That could mean the amount of dark matter in those galaxies could be much higher than believed, by 10 times or more.
To confirm these findings, the team conducted spectroscopic observations of the suspect galaxies. Visible light shifts allowed the scientists to calculate the velocity of orbiting stars, which is one of the few ways we can measure dark matter. This analysis confirmed there was much more dark matter than current models predict.
We don’t know what this means yet, but any discrepancy between models and reality is an opportunity to improve the models. That could help us figure out what dark matter is.
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