Bar Galaxies Galaxy Zoo
January 17, 2014

Spiral Galaxies Used To Be ‘Barless’, According To Galaxy Zoo

[ Watch the Video: How Have Barred Spiral Galaxies Evolved Over Time? ]

John P. Millis, PhD for - Your Universe Online

There are a number of interesting puzzles in astronomy that have faced significant challenge because the analysis simply requires massive amounts of data and complicated algorithms that demands serious computing power. Luckily, in at least some of these cases, the same algorithms that are a difficult for a computer to execute are relatively easy for our brains to decipher. Even better? You don’t even have to be particularly talented in math or science to contribute.

The crowd sourcing based project Galaxy Zoo: Hubble, is based on the idea that a person can relatively quickly identify the difference between a galaxy that is elliptical, spiral, barred spiral, irregular, etc. And because of the massive numbers of people involved, even if a particular person gets one wrong, on the average, people will get it right most of the time. In the end, galaxies can be identified simply by allowing the general public to sift through Hubble images online, and identify by clicking the button corresponding to what type of galaxy they think is on their screen at that moment.

After years of active participating by the public – and a host of interesting discoveries by amateur astronomers and enthusiasts – the Galaxy Zoo project is releasing its first scientific finding to come out of the data. Tom Melvin, a postgraduate researcher at the University of Portsmouth, examined the galaxies that the citizen astronomers had classified as spirals. But particularly, he was interested in those that were found to have a 'bar' across the central bulge.

This subset of spiral galaxies, naturally known as barred spiral galaxies, is found to have members across the cosmos. Some suggest that perhaps our own Milky Way is a member of this class. Melvin’s focus was attempting to see if there was evidence available about how the presence of these galaxies evolved over time.

When we study the more distant galaxies in our Universe – those that are billions of light years away – we are seeing them as they appeared billions of years ago. This, in essence, allows us to look back into time and see how the Universe looked in the distant past. So Melvin calculated what percentage of spirals appeared to be barred, and compared that to how distant they were.

He found that in the early Universe – some 8 billions years ago – only about 11 percent of spirals were barred. But by about 2.5 billion years that fraction had risen to 22 percent. Now, the value is estimated to be greater than 65 percent. Melvin notes, “This is a really interesting result which has been made possible by the contributions of citizen scientists, who yet again are helping cutting edge astronomical research when they spend time classifying galaxies at Galaxy Zoo.”

This result may suggests that the presence of a bar signifies maturity in the spiral galaxy, and may even play a role in the slow down of star formation. Karen Masters, project scientist for Galaxy Zoo and Professor at Portsmouth University adds, “It looks as though bars really are bad for spiral galaxies. As a bar grows in a galaxy, it is less likely to have any new stars being born and the galaxy settles down to a sedate maturity.”