Why Helium was the Dark Matter of its Day

We know it's out there. It makes up a sizable chunk of the universe. We see evidence of it in stellar objects through modern scientific tests. And yet we can't find it anywhere. What is this mysterious substance? It's helium, circa the mid-nineteenth century.

Find out how the riddle of helium consumed scientists 150 years ago, and discover the proof that almost any mystery can be resolved.

Will, one day, dark matter be a child's party favor? It seems impossible, and yet we have historical proof that such an unthinkable thing has happened every time we see a kid go by with a balloon tied to their wrist. The helium that we stuff into party balloons was once a strange substance that we found evidence of in the farthest reaches of the known universe, but that we couldn't find anywhere on Earth.

In the middle of the 1800s, scientists couldn't stop puzzling over the strange data that they kept finding. When they looked at the sun and at other stars through spectroscopes, they found a funny line, a frequency of light that was emitting by something, but not by any element that they had gotten their hands on yet. This was not a negligible trace of plasma or whiff of gas. This was a full twenty-four percent of the mass of stars in the galaxy. Because it seemed a solely stellar element, in 1868 it was named 'helium,' after Helios, the sun god. It was clearly a massive chunk of the universe of which we were a part, but no one could get their hands on it.

This makes sense, since what helium there was to be had on the surface of the world bobbled up into the atmosphere and off into space. Helium is a noble gas, which means it tends not to react chemically to anything. It melts and then steams away at temperatures too low to be practical on Earth.

Why Helium was the Dark Matter of its Day

For over twenty years, people puzzled over this elusive element, until Sir William Ramsey went looking for argon in 1895. He grabbed a chunk of cleveite, a uranium mineral, and broke it down with sulfuric acid. While analyzing the products of the dissolving hunk of rock through a spectroscope, he noticed a single yellow line forming. This yellow line looked familiar, and when he double-checked it with the light from the sun, the two were exactly the same. The elusive element was found on Earth at last. Ramsey got the 1904 Nobel Prize for Chemistry for his remarkable discovery. He also pointed people in the right direction when it came to finding the element.

A helium nucleus is also known as an alpha particle. It's often springs out from a decaying radioactive element. The early scientists knew that they could find helium in uranium, and through the early twentieth century, as radioactivity became more understood, more scientists knew where to turn. Great uranium deposits lie under the ground, and where there is uranium, there's a lot of helium, trapped in underground reservoirs. People began tapping those reservoirs of natural gas so efficiently that helium is now a common element (although we are depleting our deposits at such a rate that they may not last the century). Over about a century, helium worked its way from mysterious galactic substance to child's plaything. Who knows what dark matter will be in a hundred years?

Top Image: Up

Second Image: Pslawinski

Via The Physics Book, Nobel Prize.org, and St Andrews.