Galaxy
A spiral galaxy, 23 million light years away, has greater spin than a clumpy galaxyNASA's Marshall Space Flight Center/Flickr

The rate at which a galaxy spins determines whether it appears 'clumpy', or as a 'spiral', say researchers. Previous theories suggested that it was the high levels of gas that determine the appearance of galaxies to astronomers, but new research suggest it is actually the amount of spin.

Some galaxies appear clumpy to astronomers – as in, a lack of pattern; almost like a splodge of paint on a blank canvass. This study, published in Astrophysical Journal, shows that it is caused by low spin. Other galaxies – including our very own Milky Way – are spiral-shaped, as they spin quicker.

"While the Milky Way appears to have a lot of spin, the galaxies we studied here have a low spin, about three times lower," explained Danail Obreschkow, from the University of Western Australia. "The clumpy galaxies produce stars at phenomenal rates. A new star pops up about once a week, whereas spiral galaxies like our Milky Way only form about one new star a year."

Spiral and clumpy galaxies
The shape of spiral galaxies (left) and clumpy galaxies (right) are different. Clumpy galaxies have far more star-forming gas (red), whilst spiral galaxies have the least amount of this gas (blue)Danail Obreschkow, ICRAR/Hubble Space Telescope

The study, from the International Centre for Radio Astronomy Research, focused their investigation on rare galaxies known as the dynamo galaxies. The group is formed of 95 galaxies, and angular momentum measurements – or spin measurements – were taken for each of these dynamo galaxies using equipment able to spot them when usually they are too far away to measure.

The way that the galaxies were measured means that when the scientists were observing them, they were actually taking measurements from 500 million years ago. The researchers don't believe it will make any difference to the end results though, because they do not expect much would have changed in that time.

"We see that galaxy the way it probably looks now... something could have happened to it but it's very unlikely," said Obreschkow. He likened it to looking at a photo of yourself from a year ago – very slight differences, but probably nothing drastic. "The galaxies that are 10 billion light years away [though], that's comparable to a picture from when you were three or four years old, that's very different."

The first discovery of spinning galaxies came just over 100 years ago in 1914. Indiana-born Vesto Slipher discovered the rotation of spiral galaxies by using early spectroscopy.