Free Astronomy Magazine November-December 2022

NOVEMBER-DECEMBER 2022 novae. If R136a1 is less massive than previously thought, the same could be true of other massive stars and consequently pair instability super- novae may be rarer than expected. The star cluster hosting R136a1 has previously been observed by as- tronomers using the NASA/ESA Hubble Space Telescope and a vari- ety of ground-based telescopes, but none of these telescopes could ob- tain images sharp enough to pick out all the individual stellar mem- bers of the nearby cluster. Gemini South’s Zorro instrument was able to surpass the resolution of previous observations by using a technique known as speckle imag- ing, which enables ground-based telescopes to overcome much of the blurring effect of Earth’s atmos- phere. By taking many thousands of short-exposure images of a bright object and carefully processing the data, it is possible to cancel out al- most all this blurring. This approach, as well as the use of adaptive optics, can dramatically in- crease the resolution of ground- based telescopes, as shown by the team’s sharp new Zorro observa- tions of R136a1. “This result shows that given the right conditions an 8.1-meter tele- scope pushed to its limits can rival not only the Hubble Space Tele- scope when it comes to angular res- olution, but also the James Webb Space Telescope,” commented Ri- cardo Salinas, a co-author of this paper and the instrument scientist for Zorro. “This observation pushes the boundary of what is considered possible using speckle imaging.” “We began this work as an ex- ploratory observation to see how well Zorro could observe this type of object,” concluded Kalari. “While we urge caution when interpreting our results, our observations indi- cate that the most massive stars may not be as massive as once thought.” Zorro and its twin instrument `Alopeke are identical imagers mounted on the Gemini South and Gemini North telescopes, respec- tively. Their names are the Hawai- ian and Spanish words for “fox” and represent the telescopes’ re- spective locations on Maunakea in Hawai’i and on Cerro Pachón in Chile. These instruments are part of the Gemini Observatory’s Visiting Instrument Program, which enables new science by accommodating in- novative instruments and enabling exciting research. Steve B. Howell, current chair of the Gemini Obser- vatory Board and senior research scientist at the NASA Ames Re- search Center in Mountain View, California, is the principal investiga- tor on both instruments. “Gemini South continues to en- hance our understanding of the Universe, transforming astronomy as we know it. This discovery is yet another example of the scientific feats we can accomplish when we combine international collabora- tion, world-class infrastructure, and a stellar team,” said NSF Gemini Program Officer Martin Still. T his comparison image shows the exceptional sharpness and clarity of the Zorro imager on the 8.1-meter Gemini South telescope in Chile (left) when compared to an earlier image taken with the NASA/ESA Hubble Space Telescope (right). The new Gemini South image allowed astronomers to clearly distinguish the star R136a1 from its nearby stellar companions, providing the data needed to reveal that – while still the most massive star known in the Universe – it is less massive than previously thought. [International Gemini Observatory/NOIRLab/NSF/AURA. Ack.: Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab); NASA/ESA Hubble Space Telescope] !