Tuesday, August 23, 2022

STELLA R136a1, THE MOST KNOWN MASSIVE STAR IN THE UNIVERSE

Using the capabilities of the 8.1-meter Gemini South telescope in Chile, part of the Gemini International Observatory operated by NSF's NOIRLab, astronomers have obtained the sharpest image ever seen of the star R136a1, the best-known massive star in the universe.

 Their research, led by NOIRL astronomer Venu M. Kalari, challenges our understanding of the most massive stars and suggests they may not be as massive as previously thought.

 Astronomers have yet to fully understand how the most massive stars, those with a mass over 100 times that of the Sun, are formed.

 A particularly challenging piece of this puzzle is getting observations of these giants, who typically inhabit the densely packed hearts of dust-shrouded star clusters.  Giant stars also live fast and die young, burning up their fuel reserves in a few million years.

 By comparison, our sun is less than half its 10 billion year old.

 The combination of densely packed stars, relatively short lifetimes, and large astronomical distances makes distinguishing single massive stars in clusters a daunting technical challenge.

 By augmenting the 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 ever seen of R136a1, the most massive star known.

 This colossal star is a member of the star cluster R136, which is located approximately 160,000 light-years from Earth at the center of the Tarantula Nebula 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.

 Zorro's new observations, however, indicate that this giant star may only be 170 to 230 times the mass of the Sun.

 Even with this lowest estimate, R136a1 still qualifies as the most massive star known.

 Astronomers can estimate the mass of a star by comparing the observed brightness and temperature with theoretical predictions.

 The sharper image of Zorro allowed NSF astronomer NOIRLab Venu M. Kalari and colleagues to more accurately separate the brightness of R136a1 from its nearby stellar companions, leading to a lower estimate of its brightness and, therefore, its mass.

 "Our results show us that the most massive star we currently know is not as massive as we previously thought," said Kalari, lead author of the paper published in The Astrophysical Journal.

 "This suggests that the upper limit of stellar masses may even be smaller than previously thought."

 This finding also has implications for the origin of elements heavier than helium in the universe.  These elements are created during the explosive cataclysmic death of stars over 150 times the mass of the Sun in events astronomers refer to as pair-unstable supernovae.

 If R136a1 is less massive than previously thought, the same could be true for other massive stars, and as a result supernovae with torque instability 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 have been able to obtain images sharp enough to locate all individual stellar members. cluster close cluster.

 Source: The Astrophysical Journal

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