• Michael Curzan

In Favor of Dark Matter

Currently, there is a great mystery in astronomy. Galaxies have been observed to spin much faster around the edges than they should be able to, meaning that a truly vast amount of an unseen substance is out there, causing it to spin faster due to all this extra invisible mass. But what is this substance which we cannot directly detect? We know that it must make up by far the majority of all matter in the Universe in order for the Universe to have formed galaxies like we know them at all. However, it doesn't interact with light, and even though it outnumbers regular matter, we have so far only able to infer that it exists at all rather recently, since it was first proposed in the 1930s, and it was first used to explain the rotation rates of galaxies in the 1970s. Scientists call this mysterious component of the Universe "dark matter", and an ongoing problem is what this substance actually is. Ever since the 1930s, researchers have made steps to unravel this mystery, but we have still not yet achieved a definitive answer, only many answers that turned out to be incorrected when they were disproven in tests and observations.

While today the theory that dark matter is responsible for this mystery is definitely widespread and accepted, it wasn't always this way. In fact, there was a time when new scientists were trying to figure out if dark matter was really the answer, and they made observations and predictions that at first appeared to be evidence against the existence of dark matter. One of these theories and predictions, proposed around 20 years ago, was that if galaxies were surrounded by dark matter, as dark matter proponents suggested, then the enveloping cloud of dark matter would severely slow the rotation of the bars in the centers of spiral galaxies, which could be observed, and that should be able to settle once and for all whether this dark matter really existed at all.

When astronomers observed the bars of these spiral galaxies, they found, after applying their best methods of determining the speed of rotation of the bar in the center, that most galaxies have bars that rotate too fast for dark matter to be slowing them down in the middle. This apparently cast doubt upon the whole concept of dark matter, and until a few years ago, it seemed that dark matter might have been disproved, and astronomers would have to rethink their whole theory. But recently, a new study came along that rekindled evidence in favor of the dark matter theory, by reconciling the bar spin rates with the existence of large amounts of dark matter around a galaxy.

A new series of observations of spin rates in galaxies has revealed that the measurements and findings that seemed to disprove dark matter were actually incorrect. By using and developing more precise methods to measure the rotation rates, a new group of astronomers managed to find out that the seemingly contradictory evidence towards the existence of dark matter halos around galaxies could be explained by the fact that the bars in the middle of galaxies could grow or shrink as they changed speeds, which complicated everything and ended up with scientists needing to really adjust their measurement techniques in order to account for this effect. When they did so, they found that now, the bars appeared to really be slowing down, confirming that dark matter might still be there after all.

This fixing of the theory of dark matter that made it plausible again relied on a hypothesis that the bars of a galaxy could change size as well as speed in order to account for the observations made of galaxies spinning. This hypothesis would fix everything, but it had to be tested first in order to give it some credibility. So computer simulations were made of galaxies with bars, and how the bars might form and change size and speed throughout time, under the effects of dark matter. Computer simulation always seems to be a valuable and often-used tool for scientists and specifically astronomers, at least in recent years. These models confirmed that this hypothesis would indeed work, thus validating the new model that fixes the dark matter problem as it pertains to galaxy bars.

This story of how dark matter came under questioning, yet emerged stronger than ever, shows how the scientific method works. A theory is proposed, in this case dark matter. New evidence comes along in an attempt to disprove it, in this case the bars of spiral galaxies and how fast they rotate. And then a new hypothesis comes along in order to explain the new data, in this case, the hypothesis that the bars could change size over time, which was validated by computer testing with simulated models. And computer testing is currently a large step in the scientific process, in addition to the obvious parts such as hypothesizing and testing the hypothesis with observations that may end up refuting it, possibly. So this tells us, in the end, that the process of the scientific method is still working as strongly as it ever has before. Science is still very much alive.

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