Astronomers have discovered two stores of cosmic firecrackers deep in the galaxy, they will reveal today. The rare clusters contain 40 ancient stars all primed to explode as supernovae – the biggest blasts seen within the Milky Way.

Both star clusters are around 20,000 light-years away in a straight region called the Galactic Bar which runs across the spiral pattern of our home galaxy. They lie 800 light-years apart.

The stars are Red Supergiants right at the end of their life cycles. However, it is impossible to predict exactly when they will be seen to explode.

Since they lie so far away, it is possible that some have aleady erupted and the light of their blasts is still racing across space to reach us.

A supernova briefly becomes as bright as all the billions of other stars in the galaxy combined as it blows itself to pieces.

Dr Ben Davies will announce the discovery of the clusters, in the constellation of Scutum, the shield, today at the National Astronomy Meeting in Belfast organised by the Royal Astronomical Society.

He said yesterday: Red Supergiants, or RSGs, represent the final brief stage in a massive star’s lifecycle before it goes supernova. They are very rare objects, so to find this many in the same place is remarkable.

“Together they contain 40 RSGs, which is nearly 20 per cent of all the known RSGs in the Milky Way. These stars are all at the brink of going supernova.”

Cluster 1 contains 14 RSGs and is 12 million years old. Cluster 2 contains 26 RSGs and is 17 million years old. Massive stars are rarely observed because they burn their fuel up very quickly. RSGs are rarer still because they are only a brief period of that short life cycle.

Dr Davies, of the Rochester Institute of Technology, New York, added: “The next supernova could go off in one of these clusters at any time. We estimate that it’s about 5,000 years between explosions for these clusters and we can see the remnants of a supernova that went off around 5,000 years ago. That means that the next one could be any time between today and 7008 AD.”

The team first spotted the clusters in a survey of the galaxy made by Nasa’s heat-seeking Spitzer Space Telescope. Their exact positions were then pin-pointed using a giant telescope on Hawaii.

It is hundreds of year since a supernova was seen in our own Milky Way but they are regularly spotted in distant galaxies since there are so many of them. A supernova in a satellite galaxy of the Milky Way 21 years ago later revealed a stunning ring-of-pearls effect.

Picture: One of the clusters spotted by the team.

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