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heic1605a_625Astronomers have identified nine monster stars which are over 100 times the mass of the Sun using the NASA/ESA Hubble Space Telescope. The discovery of the star cluster named R136 is the largest sample of very massive stars identified to date and has raised many new questions about the formation of massive stars. The international team of scientists, led by researchers from the University of Sheffield, combined images taken with the Wide Field Camera 3 with the unprecedented ultraviolet spatial resolution of the Space Telescope Imaging Spectrograph (STIS) to successfully dissect the young star cluster in the ultraviolet for the first time.

R136 is only a few light-years across and is located in the Tarantula Nebula within the Large Magellanic Cloud about 170,000 light-years away. The young cluster hosts many extremely massive, hot and luminous stars whose energy is mostly radiated in the ultra violet â which is why the scientists probed the ultraviolet emission of the cluster. As well as finding a total of nine very massive stars, over 100 times more massive than the sun, the new study also revealed dozens of stars exceeding 50 solar masses. The detected stars are not only extremely massive, but also exceptionally bright and together the nine massive stars outshine the Sun by a factor of 30 million.

Professor Paul Crowther, from the University of SheffieldâÂÂs Department of Physics and Astronomy and lead author of the study, said: âÂÂOnce 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. âÂÂThe 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.âÂÂTogether with my colleagues, I would like to acknowledge the invaluable work done by astronauts during HubbleâÂÂs last servicing mission: they restored STIS and put their own lives at risk for the sake of future science.âÂÂ

In 2010 Professor Crowther and international team of collaborators showed the existence of four stars within R136, each with over 150 times the mass of the sun. At that time the extreme properties of these stars came as a surprise as they exceeded the upper-mass limit for stars that was generally accepted at the time. Now, this census, published in the monthly notices of the Royal Astronomical Society,à has shown that there are five more stars with more than 100 solar masses in R136 raising many new questions about the formation of massive stars as the origin of these huge creations remains unclear.

Saida Caballero-Nieves, also from the University of Sheffield and co-author of the study, said: âÂÂThere have been suggestions that these monsters result from the merger of less extreme stars in close binary systems. From what we know about the frequency of massive mergers, this scenario canâÂÂt account for all the really massive stars that we see in R136, so it would appear that such stars can originate from the star formation process.âÂÂ

In order to find answers about the origin of these stars the team will continue to analyse the datasets gathered. An analysis of new optical STIS observations will also allow them to search for close binary systems in R136, which could produce massive black hole binaries which would ultimately merge, producing gravitational waves. Despite the new discovery the current record holder R136a1 does keep its place as the most massive star known in the Universe at over 250 solar masses. The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The results were published in the paper âÂÂThe R136 star cluster dissected with Hubble Space Telescope/STIS. I. Far-ultraviolet spectroscopic census and the origin of Heii û1640 in young star clustersâ in the Monthly Notices of the Royal Astronomical Society.”