The gas in a galaxy glows like a neon sign, and by the color of that glow, astronomers can tell how hot it is. The logic is simple: the more heavy elements (which astronomers call metals) in the gas, the better it cools. So galaxies rich in metals should have cooler gas. But new observations show the opposite.
The researchers took two independent datasets and measured the temperature using the glow of ionized oxygen. It turned out that in galaxies with high metal content, the temperature doesn't drop: it rises. It's as if, on a hot day, the air conditioner didn't cool the room but heated it instead.
No one can yet explain why this happens. It's not a measurement error or the effect of dust. Perhaps the oxygen in such galaxies is being lit up by some extra source of energy. If no cause is found, we'll have to rethink the very method of determining the chemical composition of galaxies, and much of our knowledge about the evolution of the universe rests on it.
The thermometer we've been using to measure galaxies for decades seems to need recalibration.
In astronomy, 'metals' are all elements heavier than helium, even oxygen and nitrogen — chemically incorrect, but that's the tradition.
In 'Star Trek', the composition of distant worlds is determined instantly, but if our method is flawed, even fictional scientists would have to recalibrate their instruments.