What is a galaxy? Cast your vote here…
In a unique public engagement exercise, Swinburne University is calling on amateur astronomers and members of the public to help answer the question, ‘What is a galaxy?’
While the term galaxy is bandied around regularly by scientists and the broader community, no clear definition exists for what constitutes a galaxy.
This is why Swinburne astrophysicist Professor Duncan Forbes and his colleague Professor Pavel Kroupa from the University of Bonn have launched a website (www.surveymonkey.com/s/wlrjmws) where science-savvy members of the public can read a short paper on the subject and vote for their preferred definition.
According to Forbes and Kroupa, there is a general understanding in the astronomy community that a galaxy is a massive, gravitationally bound stellar system.
However there is no consensus as to how big a system has to be in order for it to be considered a galaxy and what differentiates a small galaxy from a large star cluster.
“I think it is important to have a clear definition and well defined process for determining what is a galaxy. Such a process may provide new insight into how galaxies form and evolve with time” said Forbes.
According to Forbes the circumstances that surrounded the stripping of Pluto’s ‘planet status’ inspired him to take a more democratic approach to galactic classification.
“The decision of how to define a small planet was made by around 400 astronomers present at the last day of the International Astronomical Union General Assembly in Prague in 2006.”
“As a result of the new definition, which was quite divisive, Pluto was effectively kicked out of the planetary club.”
When deciding on what should and shouldn’t be considered a galaxy, Forbes and Kroupa wanted to take a more inclusive approach.
“We wanted to use the wisdom of crowds to help us come up with a working definition and engage a wider community. Anyone can vote on the website. People can choose from several suggested definitions for a galaxy, based on factors such as size, motions of stars and the presence of cold dark matter and satellites. They can also suggest their own definition.”
Forbes said one stellar system that may be impacted by a new definition is Omega Centauri, which when viewed with the naked eye appears as large as the full moon.
“Although many amateur astronomers know Omega Cen as massive star cluster, some professional astronomers regard it as a galaxy. This is a stellar system that could be upgraded or downgraded by this exercise, depending on your point of view.
“Hopefully the results of the poll will help the scientific community come to a consensus about what a galaxy actually is,” Forbes said. He aims to report the survey results at an upcoming scientific conference.
The researchers’ exercise follows a number of other public engagement activities from astronomers around the world.
One of the most well known of these is Galaxy Zoo, an online astronomy project which invites members of the public to help an international team of astronomers classify over sixty million galaxies.
Others include Einstein@Home, which uses the idle time of volunteers’ home computers to search the Universe for pulsars and the SETI Program (Search for Extra Terrestrial Intelligence), which using open-source code, asks volunteers to analyse real-time data from telescopes.
“Many people are interested in astronomy and opportunities like these allow them to make a real contribution,” Forbes said.
‘What is a Galaxy? Cast you vote here…‘ has been accepted for publication in the Publications of the Astronomical Society of Australia and is available at arxiv.org/abs/1101.3309
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