By harnessing the capabilities of the 8.1-meter Gemini South Telescope in Chile, part of the Gemini Global Observatory operated by NSF’s NOIRLab, astronomers have obtained the sharpest image ever seen of the star R136a1, the most massive star known in the Universe . Their research, led by NOIRLab astronomer Venu M. Kalari, challenges our understanding of the most massive stars and suggests that they may not be as massive as previously thought.
Astronomers have yet to fully understand how the most massive stars form – those with more 100 times the mass of the Sun. A particularly difficult piece of this puzzle involves obtaining sightings of these giants, which typically inhabit the densely populated cores of dust-shrouded star clusters. Giant stars also live fast and die young, burning up their fuel reserves in just a few million years. By comparison, our Sun is less than halfway through its lifespan of 10 billion years. The combination of dense stars, relatively short lifetimes, and vast astronomical distances makes differentiating individual massive stars in clusters a daunting system challenge.
Pushing capabilities of the Zorro instrument on the Gemini International Observatory’s Gemini South Telescope, operated by NSF’s NOIRLab, astronomers have obtained the sharpest image of R136a1, the most substantial known star. This colossal star is part of the R136 star cluster, which lies about 160 10 light years from Earth to the center of the nebula of the Tarantula in the Large Magellanic Cloud, a dwarf galaxy companion to the Milky Way.
Previous observations suggested that R136a1 had a mass between 250 and 320 times the mass of the Sun. New Zorro observations, however, indicate that this giant star may only have 170 to 230 times the mass of the Sun. Even with this lower estimate, R136a1 still qualifies as the largest known star.
Astronomers are able to estimate the mass of a star by comparing its observed luminosity and temperature with theoretical predictions. The sharper image of Zorro allowed NSF NOIRLab astronomer Venu M. Kalari and colleagues to more accurately separate the luminosity of R136a1 of its close stellar companions, which led to a lower estimate of its luminosity and therefore of its mass.
“Our results show us that the he most enormous star we know of right now is not as large as we previously thought,” explained Kalari, lead author of the paper announcing the result. “This suggests that the upper limit of stellar masses may also be smaller than previously thought.”
This result also has implications for the origin of larger elements. heavier than helium in the Universe. These elements are created during the cataclysmic explosive death of stars more than 150 times the mass of the Sun in events that astronomers call pair-instability supernovae. If R136a1 is less massive than previously thought, so could other massive stars and, therefore, pair-instability supernovae may be rarer than expected.
The star cluster hosting R136a1 has previously been observed by astronomers using the NASA/ESA Hubble Space Telescope and a variety of ground-based telescopes, but none of these telescopes could obtain images sharp enough to pick out all the individual stellar members of the nearby cluster..
The Zorro Instrument from Gemini South was able to surpass the resolution of previous observations by using a technique known as speckle imaging, which allows ground-based telescopes to overcome much of the blurring effect of Earth’s atmosphere. By taking several thousand short-exposure images of a bright object and carefully processing the data, it is possible to cancel out almost all of this blurring. This approach, along with the use of adaptive optics, can increase the resolution of ground-based telescopes considerably, as shown by the team’s new precise observations of Zorro on the R136a1..
“This result shows that in the right conditions, an 8.1-meter telescope pushed to its limits can compete not only with the Hubble Space Telescope in terms of angular resolution, but also with the James Webb Space Telescope,” commented co-author Ricardo Salinas. “This observation pushes the boundaries of what is considered feasible using speckle imaging.”
“We started this work as an exploratory observation to see how Zorro could observe this kind of object,” Kalari concluded. “Although we urge caution when interpreting our results, our observations indicate that the most massive stars may not be as massive as previously thought.”
Zorro and its twin instrument `Alopeke are identical imagers mounted respectively on the Gemini South and Gemini North telescopes. Their names are the Hawaiian and Spanish words for “fox” and represent the respective locations of the telescopes on Maunakea in Hawai’i and on Cerro Pachón in Chile. These instruments are part of Gemini Observatory’s Visiting Instrument Program, which enables new science by hosting innovative devices and enabling exciting research. Steve B. Howell, current Chairman of the Gemini Observatory Board and Principal Investigator at NASA Ames Research Center in Mountain View, California, is the Principal Investigator for both instruments.
“Gemini South continues to improve our understanding of the Universe, transforming astronomy as we know it. know. This discovery is another example of the scientific feats we can achieve when we combine international collaboration, world-class infrastructure and a stellar team,” said Martin Continue to, NSF Gemini Program Manager.
The blurring effect of the atmosphere is what makes the stars twinkle at night , and astronomers and engineers have developed a variety of approaches to deal with atmospheric turbulence. In addition to placing observatories on high, dry sites with secure skies, astronomers have outfitted a handful of telescopes with adaptive optics systems, computer-controlled deformable mirror assemblies, and laser guide stars. that can correct atmospheric distortion. In addition to speckle imagery, Gemini South is able to use its Gemini multiconjugate adaptive optics system to counter atmospheric blurring.
Observations individual images captured by Zorro had exposure times of only 60 milliseconds, and 40 10 of these individual observations of cluster R136 were captured in 10 minutes. Each of these snapshots is so short that the atmosphere did not have time to blur an individual exposure, and carefully combining the 40 000 exposures, the team was able to create a clear image of the cluster.
When observing in the red portion of the noticeable electromagnetic spectrum (approximately 832 nanometers), the Zorro instrument on Gemini South has an image resolution of approximately 10 milliarcseconds. This is a slightly better resolution than the NASA/ESA/CSA James Webb Space Telescope and approximately three times the sharper resolution achieved by the Hubble Space Telescope at the same wavelength.