The movement of bubbling gas on the surface of the star R Doradus
ALMA (ESO/NAOJ/NRAO)/W. Flemish
Giant bubbles of hot gas, more than 75 times the size of our sun, have been observed on the surface of a nearby star, which researchers say could lead to better solar computer simulations.
Wouter Vlemmings and colleagues at Chalmers University of Technology in Gothenburg, Sweden, hoped to observe R Doradus, which is 178 light-years from Earth and 350 times larger than the sun, to better understand how matter is ejected from aging stars.
Vlemmings says they booked time with the Atacama Large Millimeter/Submillimeter Array (ALMA) observatory in Chile, where only one in seven requests succeeds, to collect a single instantaneous observation.
The first two attempts were hampered by Earth’s weather conditions, so only the third met the strict quality criteria set out in the researchers’ request for observation time. But that meant they accumulated multiple images, all of which Vlemmings said were usable, allowing the team to trace movement over time.
Not only was this the first time such bubbles had been observed in detail outside our solar system, but the images also formed a sort of flipbook, allowing researchers to assess their speed as well as their size. “That was a bonus,” Vlemmings says. “We didn’t plan for this, and we certainly didn’t expect everything to fall into place (this way).”
They also found that the giant gas bubbles, measuring more than 100 million kilometers from side to side, surfaced and then fell back inside the star faster than expected.
Nuclear fusion reactions inside stars create convection currents, where hot gas bubbles rise to the surface before cooling and sinking toward the core. This process is thought to be responsible for the ejection of material which then escapes a star’s gravity and spreads throughout the cosmos to form new stars and planets. It now appears to be happening three to four times faster than expected, at least in R Doradus, where the bubbles form and disappear in about a month.
The region around R Doradus
ESO/Digitized Sky Survey 2
Convection on stars has been modeled by computer for some time, but these models now seem to be a bit lacking because the motion is not as fast as is currently observed in the real world, Vlemmings says.
“It seems like something is missing, because these bubbles are a little faster than expected,” he says. “For a long time in our field, models have been ahead of observations, but we never had observations to test whether those models were correct.”
R Doradus had not been the subject of much research in the past because it can only be seen from the southern hemisphere and, historically, most large radio telescopes were in the northern hemisphere. But Vlemmings says that has changed with ALMA. It also produces data so complete that he expects more remains will be discovered. Researchers hope to observe similar stars next year to see if they can find the phenomenon elsewhere.
