Most of the biggest and brightest stars we have ever observed are packed in a cluster not even 170,000 light-years away from us. And now, Hubble has spotted even more giant stars in the group.

The space telescope has identified nine huge stars with masses over 100 times the mass of the Sun in the star cluster R136, which is located in the Large Magellanic Cloud. Together these nine stars are 30 million times brighter than the Sun. The results are published in the Monthly Notices of the Royal Astronomical Society,

The team also found dozens of 50-solar-mass stars in the cluster, all packed into an area a few light-years in diameter. The observations were made possible by the last upgrade performed on Hubble in 2009, which dramatically improved the spatial resolution in the ultraviolet by repairing the Space Telescope Imaging Spectrograph (STIS). These bright, big stars are ultraviolet powerhouses, so Hubble has finally been able to resolve them individually.

"The ability to distinguish ultraviolet light from such an exceptionally crowded region into its component parts, resolving the signatures of individual stars, was only made possible with the instruments aboard Hubble," explained Paul Crowther from the University of Sheffield, lead author of the study, in a statement.

"Together with my colleagues, I would like to acknowledge the invaluable work done by astronauts during Hubble's last servicing mission: They restored STIS and put their own lives at risk for the sake of future science!"

^{Shown is the cluster R136 as seen in the ultraviolet. ESA/Hubble, NASA, K.A. Bostroem (STScI/UC Davis)}

R136 hosts the largest, brightest star ever observed, R136a, which has a mass of 265 Suns and is 8.7 million times the luminosity of our own star. This star and three more with a mass of 150 solar masses were discovered by Crowther and his collaborators in 2010. The observations are incredible, but how these stellar behemoths form is still very mysterious.

"These newly found stars are pushing the theoretical limits of what is possible in terms of a star’s existence," said Dr. Chris Pearson, an RAL Space astronomer at Harwell Campus in the U.K., in a comment sent to IFLScience. “Due to their size, they will burn much faster and brighter than our Sun, meaning they will have significantly shorter lifespans measured in millions rather than billions of years.”

This research is a significant step forward in our understanding, but the team will continue observing this cluster in the hope of finding more clues on how these stars form.

"Once again, our work demonstrates that, despite being in orbit for over 25 years, there are some areas of science for which Hubble is still uniquely capable," said Crowther.