Free Astronomy Magazine May-June 2016

SPACE CHRONICLES STIS and put their own lives at risk for the sake of future science!” In 2010 Crowther and his collabora- tors 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 ex- ceeded the upper-mass limit for stars that was generally accepted at that time. Now, this new census has shown that there are five more stars with more than 100 solar masses in R136. The results gathered from R136 and from other clusters also raise many new questions about the formation of massive stars as the origin of these behemoths remains unclear. The ul- traviolet signatures of even more very massive stars have also been re- vealed in other clusters — examples include star clusters in the dwarf gal- axies NGC 3125 and NGC 5253. How- ever, these clusters are too distant for individual stars to be distinguished even with Hubble. Saida Caballero-Nieves, a co-author of the study, explains: “There have been suggestions that these mon- sters result from the merger of less extreme stars in close binary systems. From what we know about the fre- quency of massive mergers, this sce- nario can’t account for all the really massive stars that we see in R136, so it would appear that such stars can originate from the star forma- tion process.” In order to find an- swers about the origin of these stars the teamwill continue to analyse the gathered datasets. 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, pro- ducing gravitational waves. “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 ca- pable,” concludes Crowther. n