homehome Home chatchat Notifications


Massive dying star has 'boiling' bubbles 75 times the size of the Sun

Observations of R Doradus, a nearby red giant, provide the first timescale for convection on the surface of any star other than the Sun.

Damond Benningfield
October 11, 2024 @ 1:43 pm

share Share

Three ALMA images, spaced about a week apart, show changes in the giant convection cells on the surface of the nearby star R Doradus. The size of Earth’s orbit around the Sun is shown for scale. Credit: ALMA (ESO/NAOJ/NRAO)/W. Vlemmings et al.

The outer layers of most stars are like a pot of boiling water, with giant bubbles known as convection cells transporting energy and hot gases from deep inside the star to the surface. Bubbles on the Sun are as big as Texas, and they percolate to the surface and fall again over a period of a few minutes.

Astronomers have now measured both the size and cadence of bubbles on a star other than the Sun for the first time. The star, R Doradus, is a red giant roughly 350 times the Sun’s diameter. Its convection cells are dozens of times the size of the Sun itself, and they rise and fall over a period of a few weeks. These data should help theorists revise models of the final stages of life for the Sun and similar stars.

“This result isn’t a big shock, but it’s very pleasing,” said Christopher Sneden, an astronomer at the University of Texas at Austin who wasn’t involved in the study. “It’s especially interesting because they caught an ordinary, garden-variety star,” which began life with a mass similar to the Sun. “It’s not some exotic, ‘Betelgeuse is going to explode any minute folks, run for your lives!’ kind of star. And that’s what makes this study especially welcome.”

A Mighty Big Target

Researchers were studying how dying stars eject elements created through nuclear reactions in their cores into the interstellar medium. “We are all made of ‘stardust,’ and much of the material around us is made in stars,” said Wouter Vlemmings, an astronomer at Chalmers University of Technology in Sweden and the study’s lead author. “How this material is ejected from old stars to be incorporated into new stars and planets is still not completely clear.”

R Doradus was a primary target because it is relatively close—roughly 180 light-years away—and quite large. It spans about 3.3 astronomical units (1 astronomical unit is the average distance from Earth to the Sun), so if it replaced the Sun in our own solar system, it would engulf the four innermost planets, including Earth. The combination makes R Doradus one of the largest stars in the sky.

R Doradus shines brightly in this wide-field image of its region in the constellation Dorado. Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin

R Doradus is so big because it has evolved into an asymptotic giant branch star—the final and most impressive red giant phase—as nuclear fusion shut down in its core. Today, R Doradus is fusing hydrogen and helium in thin shells around the core. Radiation from these reactions pushes on the surrounding layers of gas, inflating the star.

Despite its great expanse, R Doradus is only slightly less massive than the Sun. It probably began life no more than 1.25 times the Sun’s mass, so it gives us a preview of what the Sun will look like when it enters its own red giant phase in about 5 billion years.

The astronomers observed R Doradus with ALMA (Atacama Large Millimeter/submillimeter Array), a telescope high in the Andes Mountains of Chile, during five sessions spaced roughly 1 week apart in July and August 2023. ALMA’s high resolution allowed the team to map motions at the star’s millimeter “surface.” (Optical and shorter wavelengths can see slightly deeper into a star’s atmosphere, so “there is not a single surface that can be defined,” Vlemmings said.)

Stars twirl around some of the ALMA antennas in this long-exposure image of the array. Credit: ESO/B. Tafreshi (twanight.org)

The observations revealed convection features up to 0.72 astronomical unit in diameter—more than 75 times the diameter of the Sun. “The size corresponds well to the expectation of convection cells on these types of stars, so that’s what we think we’re seeing,” Vlemmings said.

Bubbling Faster Than Expected

Though previous studies have imaged convection cells on a few large stars—mainly red supergiants such as Antares, which are much more massive—the R Doradus study was the first to measure their velocity. It showed that the cells were moving faster than expected, bubbling up and falling away on timescales of 3 weeks to a month.

“This is the first time the timescales of convection can be measured [anywhere] except for the Sun,” Vlemmings said. “But based on theoretical extrapolations from the Sun, we were expecting the timescales to be 3 to 4 times longer.”

So far, the astronomers have no explanation for the discrepancy. They hope to learn more, however, through continued analysis of the R Doradus observations and those already made of two other stars, along with future observations of a few other target stars.

“I’d love to see this kind of observation for another star,” Sneden said. “If you see this behavior in a second star, then you know you’re on track, you know what you’re doing, and you can force the modelers to address this issue.”

Additional modeling could add insights into the next stage for R Doradus and similar stars—a planetary nebula. In this phase, the star will expel its outer layers, briefly enveloping itself in a colorful shell of expanding gas and dust. That will leave behind only a now-dead core, a white dwarf—the fate that awaits the Sun after perhaps a billion years as a red giant.

“One part of me wants to ask if this is the start of a planetary nebula,” Sneden said. “One of the standard ways people wave their hands about planetary nebulae is that there are certain big ‘burps’ from the interior, which eventually puff out even more.” “Eventually” could be millions of years in the future, Sneden said, “but millions of years is short for a star.”

This article originally appeared in Eos Magazine.

share Share

Neanderthals and early humans started burying their dead at the same time — and it may be more about competition than honoring the dead

Researchers propose a stunning new theory for why Neanderthals and humans started to bury their dead at the same time.

How Missed Warnings and Incompetence Brought Down Arecibo’s Iconic Telescope

The fall of the radio telescope was the result of many overlooked warning signs.

Bison in Canada uncover 1,000-year-old sacred petroglyphs carved by Indigenous people

The accidental discovery occurred just months after the bison were reintroduced in the area.

MIT Scientists Use Quantum Physics to Protect Sensitive Data in AI Models

Researchers use quantum mechanics to protect data in deep-learning computations.

For the first time in recorded history (130 years) Mount Fuji is snowless in November

Mount Fuji is just one of the many important landmarks affected by climate change.

Fast fashion company replaces models with AI and brags about it

The clothes they are "wearing" are real. But everything else is very, very fake.

Humans should be better at voting than monkeys. But are we, really?

When you step into the voting booth, you might think you're making a rational choice. But what if I told you that part of your brain is just doing monkey things?

AI Finds Trump’s “Simple and Divisive” Language Is Unique Among Past U.S. Presidents

When Donald Trump steps up to a microphone, his words often make waves. Whether delivering a State of the Union address or sparring in a debate, his style is unmistakably his own. But what exactly sets him apart? A new study published in PNAS Nexus delves into this question, harnessing the power of machine learning […]

Uranus' moon Miranda may also have an ocean of hidden water

Miranda, Uranus’s smallest moon, may be hiding an exciting secret.

Meet the “Flying Spaghetti Monster” Living 10,000 Feet Beneath the Ocean’s Surface

Underwater robots find over 20 new species in the "twilight zone" of the Pacific Ocean.