NASA is releasing today a Hubble Space Telescope (HST) photograph of the most remarkable star forming region in the Local Group of Galaxies, 30 Doradus. The photograph shows about 60 stars within a central tight cluster in 30 Doradus. In contrast, earlier photographs with ground-based telescopes, supplemented by mathematical analysis, have shown only 27 stars in the tight cluster, which is called R136. Before the ground-based studies showed that so many stars are present in R136, some astronomers thought it was a single, supermassive object, with as much as 3,000 times the mass of the Sun. This recent HST photograph shows even more individual stars within R136. Furthermore, its high resolution suggests that some of the stars have more than 100 times the mass of the Sun. That would make them among the most massive stars ever identified.
30 Doradus is readily visible with the naked eye from the Southern Hemisphere of Earth, although it is located in another galaxy, the Large Magellanic Cloud, at a distance of about 160,000 light-years from Earth. The late American astronomer, Harlow Shapley, stated that 30 Doradus is so bright that if it were put in place of the nearby Orion Nebula, it would cast shadows on the nighttime landscape of Earth. 30 Doradus is located in the constellation Dorado, the swordfish.
The HST photograph of 30 Doradus was made on August 3, 1990, with the Wide Field/Planetary Camera (WF/PC) of the HST for use as a finding chart in the checkout of another HST instrument, the Goddard High Resolution Spectrograph. The WF/PC produces star images with sharp cores, 0.1 arcseconds wide. This image quality is sustained over the full field of view, which is 2.7 arcminutes square. HST astronomers studying the WF/PC picture report that they can make out the central stars of the R136 cluster. They note that because the picture was taken in violet light, at wavelength 3680 angstroms, it brings out the hottest, most massive stars in the scene. Hot stars produce more blue and ultraviolet light than cooler stars. Several of the stars appear to be single objects at the resolution of the WF/PC picture. Given their brightnesses and the distance to 30 Doradus, this observation strengthens the possibility that they may be more than 100 times as massive as the Sun.
Every HST picture of star clusters should achieve the resolution demonstrated in the photograph of 30 Doradus. Such photographs, when obtained through the different colored filters on the WF/PC and the Faint Object Camera (FOC), are expected to provide detailed information on the masses of stars in the clusters. Then, knowing the mixture of masses in a cluster (i.e., how many stars of each mass are present), astrophysicists can deduce basic information on how stars form and how they produce the chemical elements present in space. All massive stars probably become supernovae, spewing out their new-made elements. By determining how many such stars are present in 30 Doradus and similar star clusters in more distant galaxies, astronomers expect to deduce more accurate information on the enrichment of chemical elements in the universe.
Goddard Space Flight Center