Hubble Unveils Monster Stars

In another example of how European technology has opened the doors of science, astronomers using the unique ultraviolet capabilities of the NASA/ESA Hubble Space Telescope have identified nine monster stars with masses over 100 times the mass of the sun.

News of the discovery, which is the largest sample of very massive stars identified to date, was carried in the latest edition of the Monthly Notices of the Royal Astronomical Society.
The Tarantula Nebula in the Large Magellanic Cloud. The young and dense star cluster R136 can be seen at the lower right of the image.

The breakthrough, made by experts from leading US and European universities and astronomies, raises many new questions about the formation of massive stars. Using the NASA/ESA Hubble Space Telescope combined images taken with the Wide Field Camera 3 (WFC3) and the ultraviolet spatial resolution of the Space Telescope Imaging Spectrograph (STIS), the scientists successfully dissect the young star cluster R136 in 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. (One light-year is approximately six 6 trillion miles.)

The cluster hosts dozens of stars exceeding 50 solar masses.

A “solar mass” is the standard unit of mass in astronomy used to indicate the masses of other stars, as well as clusters, nebulae, and galaxies. It is equal to the mass of the sun, about 4.18 nonillion pounds. A nonillion is a cardinal number represented (in the US) with thirty zeros.

The new study was able to reveal a total number of nine very massive stars in the cluster, all more than one hundred times more massive than the sun.

The detected stars are not only extremely massive, but also extremely bright. Together these nine stars outshine the sun by a factor of thirty million.

The ultraviolet analysis also allowed the scientists to investigate outflows from these monster planets. They eject material weighing up the mass of the earth every thirty days at a speed approaching 1 percent of the speed of light, resulting in extreme weight loss throughout their brief lives.
The left side of this collage shows the central part of the young star cluster R136 as it can be seen in the ultraviolet. Due to the Hubble's ultraviolet high-resolution, the individual stars in this dense cluster can be resolved and studied.

“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,” said Paul Crowther from the University of Sheffield, UK, and lead author of the study.

In 2010 Crowther and his 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 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.

Saida Caballero-Nieves, a co-author of the study, explains: “There 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 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 formation process.”

“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,” concludes Crowther.