The super star cluster known as 'Westerlund 1' is made up of around 200,000 stars - some up to a million times brighter than the sun - and is a thousand times closer than any other, so far discovered.
Westerlund 1 is estimated to be very young - somewhere between 4 or 5 million years old - and contains thousands of huge stars, some weighing 30 or 40 times more than the Sun.
The cluster has been hidden behind a huge interstellar cloud of gas and dust in the Milky Way, blocking most of its visible light and was discovered using telescopes at the European Southern Observatory.
Now the team of astronomers from Cardiff University, University College London, University of Sheffield, University of Amsterdam, the Dominion Radio Astrophysical Observatory and Universidad de Alicante will be able to probe the structure in detail to understand the finer details of star formation.
Simon Goodwin from Cardiff School of Physics and Astronomy said: "We were amazed when we discovered quite what a monster this cluster was. All other super star clusters are many millions of light years away, but Westerlund 1 is in our backyard."
Since the cluster contains so many massive stars, it is estimated than in a time span of less than 40 million years, it will be the site of more than 1,500 supernovae..
Westerlund 1 now provides astronomers with one of the most extreme environments in the Universe to understand the long standing quest of how massive stars form.