PureInsight | March 28, 2005
[PureInsight.org] (Universe Today) Summary - (Mar 22, 2005) The Milky Way has several star clusters; collections of stars pulling each other into a tight group. But now astronomers have located a super star cluster, containing hundreds of thousands of stars in a region only 6 light-years across. It's called Westerlund 1, and nobody discovered it before now because it's hidden behind thick clouds of dust. Astronomers used several of European Southern Observatory's infrared telescopes to peer through the dust and see the super cluster's true size.
Full Story - Super star clusters are groups of hundreds of thousands of very young stars packed into an unbelievably small volume. They represent the most extreme environments in which stars and planets can form.
Until now, super star clusters were only known to exist very far away, mostly in pairs or groups of interacting galaxies. Now, however, a team of European astronomers  have used ESO's telescopes to uncover such a monster object within our own Galaxy, the Milky Way, almost, but not quite, in our own backyard!
The newly found massive structure is hidden behind a large cloud of dust and gas and this is why it took so long to unveil its true nature. It is known as "Westerlund 1" and is a thousand times closer than any other super star cluster known so far. It is close enough that astronomers may now probe its structure in some detail.
Westerlund 1 contains hundreds of very massive stars, some shining with a brilliance of almost one million suns and some two-thousand times larger than the Sun (as large as the orbit of Saturn)! Indeed, if the Sun were located at the heart of this remarkable cluster, our sky would be full of hundreds of stars as bright as the full Moon. Westerlund 1 is a most unique natural laboratory for the study of extreme stellar physics, helping astronomers to find out how the most massive stars in our Galaxy live and die.
From their observations, the astronomers conclude that this extreme cluster most probably contains no less than 100,000 times the mass of the Sun, and all of its stars are located within a region less than 6 light-years across. Westerlund 1 thus appears to be the most massive compact young cluster yet identified in the Milky Way Galaxy.
: The team is composed of Simon Clark (University College London, UK), Ignacio Negueruela (Universidad de Alicante, Spain), Paul Crowther (University of Sheffield, UK), Simon Goodwin (University of Wales, Cardiff, UK), Rens Waters (University of Amsterdam) and Sean Dougherty (Dominion Radio Astrophysical Observatory).