DARK MATTER - WHERE DID IT COME FROM?

It’s eluded us for decades, but bubbles could be the answer to the universe’s most mysterious substance

- Kulvinder Singh Chadha

If something cast a shadow but you couldn’t see it, you’d be intrigued. If it did that on the scale of the universe, you’d be perplexed. If you then couldn’t find it despite your best efforts, you’d likely be frustrated. This is the situation that scientists looking for dark matter find themselves in. But dark matter doesn’t even cast shadows; it’s invisible to all electromagnetic radiation. And yet we have solid evidence that it exists. In fact, current calculations show that it comprises 80 per cent of all of the mass in the universe. Now a new study modelling dark matter as filtering through bubbles after the Big Bang may help point scientists in a new direction.

Although the mystery of dark matter can be traced as far back as Lord Kelvin, the modern breakthrough in research came in 1933. Fritz Zwicky was a Swiss astronomer working at the California Institute of Technology. Averaging the rotations of galaxies in the Coma Cluster, a large cluster of over a thousand galaxies, Zwicky noticed that their speeds were excessive. So much so, in fact, that the galaxies should have flown apart. There wasn’t enough visible matter to gravitationally bind each galaxy together. He concluded that there must be a ‘dunkle materie’ – or ‘dark matter’ – component to them, which he calculated to be 400 times what could be seen. Modern calculations have lowered this value.

Six years later, American doctoral student Horace Babcock showed dark matter present in the Andromeda Galaxy. Curiously, it was more concentrated in the periphery of the disc than the centre. This was the first indication that galaxies had dark matter ‘halos’. Then, in the late 1970s, American astronomers Vera Rubin and Kent Ford showed that galaxies contained between five and ten times more dark matter than luminous matter.