One of the features of science is that there is always a tension going on. We have standard paradigms that most scientists work within but on occasion a new result will turn up that seems to be violate the boundaries of that paradigm. What does one do then? Reject the paradigm and its associated underlying theory? Seasoned scientists know not to do that because throwing out a paradigm is not something to be undertaken lightly since good theories are hard to come by. What they do is treat the discrepant event as an anomaly meriting further study.
The community as a whole then falls into three camps: one group tries to see if the anomaly can be brought back into conformity with the paradigm by new experiments/observations and theoretical calculations. A second group takes more seriously the possibility that this might be a real effect that requires a new paradigm to accommodate and looks to see if they can find one that fits the bill. The third group, the largest by far, consists of those who are not working in that field and are thus not using that paradigm but are aware of the existence of the anomaly. They watch with interest from the sidelines to see how things fall out.
An example of this is what happened recently with the reported observation of a galaxy that did not seem to have any dark matter at all. Dark matter is the dominant paradigm in astrophysics at the moment, in which it is believed that all galaxies are immersed in a halo of this matter whose effects are seen by the gravitational forces exerted by it. The key problem is that there has been no direct detection of dark matter so its existence has not been confirmed. Hence the report of galaxy that is free of any dark matter opened up the possibility that the dark matter paradigm might be wrong.
But new analyses of data found that the anomaly can be explained away because the problematic galaxy is actually closer than had been previously thought and this removes the anomaly.
So an international team of researchers led by the Instituto de Astrofísica de Canarias (IAC) decided to take a closer look. And they found that all the anomalous measurements in the previous research that pointed to an absence of dark matter were reliant on the distance to the galaxy – 64 million light-years away.
This gave them something to work with. Using five separate methods, including photometry from the Hubble Space Telescope and the Gemini Observatory, they recalculated the distance to NGC1052-DF2.
Each method turned up the same result – NGC1052-DF2 is much closer than 64 million light-years away. According to the team’s multiple calculations, a more accurate distance would be around 42 million light-years.
Based on this new distance, the mass of the galaxy is about half of what it was thought to be previously – and the mass of the stars is only about a quarter of what previous analysis suggested.
So, not only does the galaxy itself have less mass, but the proportion of normal matter within that mass is smaller. This implies that the rest must be made up of – you guessed it – dark matter.
This does not end the story. Single experiments rarely do in science. Groups will investigate further to see if they can find further corroborating evidence for either position until finally everyone moves on to other things and the consensus view is filed under the ‘solved’ category.