Sharpest image of most massive known star reveals its true size
Astronomers have taken the sharpest images ever of the most massive star in the known universe. With these new images, the scientists were able to refine just how big this star is, and in the process revise our ideas of how big it’s possible for stars to ever get.
R136a1 is a colossal star that lies about 160,000 light-years away from Earth, in the Tarantula Nebula of the Large Magellanic Cloud, a dwarf galaxy that orbits our own Milky Way. Previous observations have estimated its mass to be between 250 and 320 times that of the Sun, making it comfortably the most massive known star.
But nailing that number down precisely is tricky. A star’s mass is estimated by measuring its brightness and temperature, and comparing that with predictions based on its type. But R136a1 is just one star within a cluster, meaning its light is drowned out by its numerous nearby neighbors.
So for the new study, astronomers took the sharpest images so far of the giant star, to help single it out and measure its mass more accurately. To do so, they used the Zorro instrument on the 8.1-m (26.6-ft) Gemini South telescope in Chile, performing a type of observation called speckle imaging.
The Earth’s atmosphere creates a blurring effect on stars and other astronomical objects, but Zorro corrects for these by snapping thousands of shots per minute, each with exposure times of only 60 milliseconds. This means that the atmosphere doesn’t have time to blur any individual shot, and when all of these are combined together a much sharper image of the star comes into focus.
Using this speckle imaging technique, as well as Gemini South’s advanced optics, the team was able to calculate R136a1’s mass more precisely. They found that it’s probably only between 170 and 230 solar masses – much lower than previous estimates, although still high enough to keep its crown as most massive known star.
The implications of this go beyond the star itself. The team says it could also indicate that the upper limit for possible star masses is lower than previously thought, which would mean that certain types of supernova would be rarer, which in turn would affect the abundance of metals in the universe.
That said, the researchers urge caution in interpreting their results. Follow-up observations could help shed more light on these questions.
The research will be published in The Astrophysical Journal. The team describes the work in the video below.