Giant bubbles on the surface of a nearby star foreshadow the future of the Sun

() –– Astronomers have for the first time observed the detailed motions of giant gas bubbles on the surface of a nearby star, rising and falling like the inside of a lava lamp.

The huge bubbles of hot gas are 75 times the size of the Sun and appear to be sinking into the star’s interior faster than expected, according to a team of astronomers at Chalmers University of Technology in Sweden.

The images show the surface of the star R. Doradus, a red giant located 180 light-years away in the constellation Dorado. The star has a diameter approximately 350 times that of the Sun and serves as a preview of its future.

In about 5 billion years, our Sun will become a red giant, swelling and expanding while shedding layers of material and likely evaporating the solar system’s inner planets, though the fate of Earth remains unclear, according to the POT.

The observations, made using Chile’s Atacama Large Millimeter/submillimeter Array (ALMA) telescope, mark the first time researchers have tracked such detailed motions on the surface of a star other than the Sun.

The findings were published Wednesday in the journal Nature.

“We wanted to observe the gas in the atmosphere surrounding the star and were hoping to find signs of the ‘convection’ bubbles that were expected to exist,” said study lead author Wouter Vlemmings, a professor of astronomy and plasma physics at Chalmers, in an email. “However, we did not expect to see them in such detail or to actually be able to see their motion.”

When stars grow old

Vlemmings and his colleagues study what happens as stars near the end of their lives.

Stars produce energy in their core through nuclear fusion, compressing hydrogen atoms to form helium. This process heats the star and fuels it for billions of years.

The energy produced in the core can reach the surface of the star through huge, hot bubbles of gas, which then sink as they cool, similar to what happens in a lava lamp.

This process, known as convection, mixes elements created in the core, such as carbon and nitrogen, throughout the star, according to the study authors. Convection is also likely responsible for stellar winds, or fast winds that can carry elements created by the star into space to help create new stars and planets.

When a star’s life ends, it runs out of hydrogen to convert to helium, causing its core to collapse. This pressure on the core also increases the star’s temperature, causing it to swell and become a red giant, according to the POT.

As they approach the end of their lives, the stars’ outer layers peel away and eventually the stars collapse or explode, releasing the elements created within them into space.

“We are all made of ‘star dust,’ and much of the material around us is made in stars,” Vlemmings said. “It is still not entirely clear how this material is ejected from old stars to be incorporated into new stars and planets.”

The team chose to observe R. Doradus because it is one of the largest and closest red giant stars, making it easy to observe. The telescope allowed them to collect high-resolution images of the star’s surface over the course of a month.

“Convection creates the beautiful granular structure seen on the surface of our Sun, but it is difficult to see on other stars,” said study co-author Theo Khouri, a researcher at Chalmers, in a statement. “With ALMA, we have now been able to not only directly see the convective granules – 75 times the size of our Sun! – but also measure how fast they are moving for the first time.”

The Sun’s outermost layer, called the photosphere, is made of gas so hot that it bubbles. The Sun’s photosphere is filled with millions of bubbles formed by convection. The gas bubbles, also known as convective granules, are about 1,000 kilometers in diameter and move at speeds of a few kilometers per second, so they only survive for about 10 minutes.

But the convective cells on the surface of R. doradus are more than 100 million kilometers (about 62 million miles) in size, with velocities of a few tens of kilometers per second, and persist for about a month.

“We don’t yet know what the reason for the difference is. It appears that convection changes as a star ages in ways we don’t yet understand,” Vlemmings said.

While convection bubbles had already been detected on the surfaces of stars, the new observations tracked the motion of the bubbles in a way that was not previously possible.

“It is spectacular that we can now directly image surface details of such distant stars and observe physics that was previously only observable on our Sun,” said study co-author Behzad Bojnordi Arbab, a PhD student at Chalmers, in a statement.

The new study includes observations that ran for longer than previous ones, which captured the evolution of the bubbles, said Dr. Claudia Paladini, an associate astronomer at the European Southern Observatory in Chile. Paladini was an author on a study on the observation of bubbles on the surface of the star pi1 GruisAlthough she was not involved in the new research, she was an author on an accompanying paper in Nature.

“You can see the bubbles rising, expanding and disappearing just like you see on the Sun. It’s amazing considering the distance we’re talking about,” Paladini said. “Now we just need to observe many more of these stars!”