Why Are Some Galaxies Clumpy?

Why Are Some Galaxies Clumpy?

Our Milky Way galaxy is a lovely, elegant spiral shape. Some galaxies aren’t quite as lucky. Some galaxies are ‘clumpy’. Early theories suggested that these clumpy galaxies may be down to high levels of gas, but new research is making it apparent that low spin is responsible for the lack of a distinct spiral shape. What’s more, these clumpy galaxies seem to be producing stars at phenomenal rates.

Dr Danail Obreschkow from The University of Western Australia claims that ten billion years ago, clumpy galaxies were much more common than they are today. As these objects evolved, they turned into the more regular spiral shapes that we see today. Most of the stars in the sky that we know now would have been formed in these clumpy galaxies, which are able to produce a new star a week. Spiral galaxies like the Milky Way, on the other hand, only form new stars approximately once a year.

The Andromeda galaxy is a spiral galaxy similar to our Milky Way. Image by Robert Gendler via NASA

The team conducting this research focussed on just a few rare examples, which are known as DYNAMO galaxies. They have remained clumpy even though they are being observed ‘only’ 500 million years in the past — which Dr Obreschkow equates with looking at a passport photo taken a year ago.

In order to measure the spin of these galaxies, the team used the Keck and Gemini observatories in Hawaii, along with millimetre and radio telescopes to measure how much gas they contained. In the end they concluded that the DYNAMO galaxies had a low amount of spin — about three times lowe than the Milky Way’s spin. This is thought to be the main reason for the galaxies’ clumpiness, rather than the high gas content.

“Today we are still revealing the important role that the spin of the initial cloud of gas plays in galaxy formation,” said Swinburne University astronomer Professor Karl Glazebrook, co-author and leader of the survey team. “This new result suggests that spin is fundamental to explaining why early galaxies are gas-rich and lumpy while modern galaxies display beautiful symmetric patterns.”