Gas bubble on another star found to be 75 times larger than the Sun

A giant bubble of hot gas more than 75 times the size of our sun has been observed on the surface of a nearby star, and researchers say this could lead to improved computer simulations of the sun.

Wouter Flemings He and his colleagues from Chalmers University of Technology in Gothenburg, Sweden, were looking at R Doradus, a star 178 light-years away from Earth and 350 times the mass of the Sun, in hopes of better understanding how material is ejected from old stars.

Vlemmings says they booked time at the Atacama Large Millimeter/submillimeter Array (ALMA) observatory in Chile — which only gets one in seven applications — and there they collected a single snapshot observation.

The first two attempts were hampered by weather conditions on Earth, and only the third met the stringent quality standards set out in the researchers' Observatory Time application, but this led to the accumulation of multiple images that Vlemmings says were in fact all usable, allowing the team to plot movement over time.

Not only was this the first time such a bubble had been observed in detail outside the solar system, but the image was shaped like a kind of flip-book, allowing the researchers to measure not only its size but also its speed. “That was a bonus,” Flemings says. “We hadn't planned for it, and certainly didn't expect it to all work out that way. [this way].”

They also discovered that giant gas bubbles, more than 100 million kilometres wide, were rising to the surface and then sinking back into the star's interior at a faster rate than expected.

Nuclear fusion reactions inside the star create convection currents, which cause bubbles of hot gas to rise to the surface, then cool and sink back to the core. This process is thought to eject material that escapes the star's gravity and spreads out into space to form new stars and planets. At least in R Doradus, this process appears to be happening three to four times faster than expected, with bubbles forming and disappearing over the course of about a month.

Stellar convection has been modeled in computers before, but those models appear to be a bit flawed because the motion isn't nearly as fast as observed in the real world, Vlemings said.

“These bubbles are moving a little faster than expected, so it seems like we're missing something,” he says. “For a long time in our field, the models have basically been ahead of the observations, but we've never really had the observations to test whether those models are correct.”

Doradus R has not been the subject of much study because it's only visible from the Southern Hemisphere, and historically most of the large radio telescopes have been in the Northern Hemisphere. But that's changed with ALMA, Vlemmings says. Because ALMA produces such comprehensive data, he hopes to find even more remnants. Researchers hope to observe similar stars next year to see if the phenomenon can be found in other places.