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31 October 2013

Why we could soon see a revolution in our understanding of the universe

The biggest known star in the universe is about to blow. This kind of thing doesn't happen every day - and when it does, something extremely interesting usually happens.

By Michael Brooks

It’s a shame that modern astronomy’s naming systems are so no-nonsense. We’re going to be considering a star that will soon explode within a constellation called Ara. Ptolemy named the constellation in the 2nd century; it means “altar”, because the Greeks saw it as the place where the gods made sacrifices and formed alliances. In Chinese astronomy, this area of the sky is known as the “azure dragon of the east”.

Meanwhile, a team of modern astronomers is talking about looking within Ara at a cluster of stars it calls Westerlund 1. The star the astronomers are interested in is W26. The instrument they’ll be using to look at it is known without irony as the “Very Large Telescope Survey Telescope”. Thankfully, what they’ve found does kindle something in the imagination.

The biggest known star in the universe is about to blow. Its radius is 1,500 times that of the sun but it is only dimly visible. Besides being about 150,000 trillion kilometres from Planet Earth, it’s also on the other side of one of the spiral arms of our galaxy. As a result, W26’s light passes through a fearful amount of dust and gas before it reaches us.

Janet E Drew of the University of Hertfordshire first spotted W26’s potential in pictures taken by the Hubble Space Telescope. According to a paper that she and her team recently published in the Monthly Notices of the Royal Astronomical Society, follow-up studies show that it is shedding mass so quickly that it will soon explode as a supernova.

This kind of thing doesn’t happen every day. Drew’s team is now applying for telescope time in order to take a closer look.

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Supernova explosions are not just pretty pictures. In the past, we have used them to seed a revolution in our understanding of the entire universe. Watching how the different colours in the spectrum of the explosion’s flash fade away gives us a way of determining not just how far the light travelled to the earth but how the space between the supernova and the earth was expanding during the light’s journey. That led us to the discovery in 1998 that the expansion of the universe is speeding up, not slowing down.

Until then, everyone had thought that the gravitational attraction between all the matter in the universe would be pulling on it, slowing down the expansion that started with the Big Bang.

Yet a survey of the light coming from various supernovae showed that something is pushing on the fabric of the universe, causing an ever-faster expansion. We still don’t know what that something is, although it has been given a name that is better than usual: dark energy.

Studying W26’s explosion is unlikely to bring us revelations on that kind of scale. However, it’s still going to be an inspiring moment.

Heavy atoms are already spewing out from the star as its surface breaks up. These atoms were manufactured in nuclear reactions powered by the high temperatures and pressures that exist deep within the body of the star and are essential to the formation of new solar systems. When W26 explodes, it will eject atoms that will seed future suns, future planets and, quite possibly, future life.

We’ve known for at least a century that all the stuff from which we, the sun and our planet are made comes from other stars. But we still don’t know where in the star the elements form or how they rise to the surface.

The idea that we are stardust is almost banal now but, happily, it still thrills and motivates the astronomers who get to work out the details of how that came to be – even if they have to use something called the Very Large Telescope Survey Telescope to do it.