Philippa Kaur

A pair of stars in our galaxy is revealing how light pushes around matter. It’s the first time anyone has directly seen how the pressure of light from stars changes the flow of dust in space.

Such radiation pressure influences how dust clears from the regions near young stars and guides the formation of gas clouds around dying stars (SN: 9/22/20). The dust pattern surrounding a stellar pair 5,600 light-years away in the Cygnus constellation is providing a rare laboratory to observe the effect in action, astronomer Yinuo Han and colleagues report in the Oct. 13 Nature. 

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Astronomers have long known that the dust emerging from the star WR 140 and its companion is formed by gas from these two stars colliding and condensing into soot. But images of the pair taken over the course of 16 years show that the dust is accelerating as it travels away from the stars.

Dust initially departs the stars at about 6.5 million kilometers per hour, the researchers report, and over the course of a year accelerates to nearly 10 million km/h. At that speed, the dust could make the trip from our sun to Earth in a mere 15 hours.

The revelation came from comparing the positions of concentric dust shells year to year and deducing a speed. The researchers’ calculations show that the force accelerating the dust is the pressure exerted by light radiated from the stars, says Han, of the University of Cambridge. “Radiation pressure [becomes apparent] only when we put all the images next to each other.”  

Not only are those layers of dust feeling light’s push, they also extend out farther than any telescope could see — until this year. Images from the James Webb Space Telescope, or JWST, depict more of the dusty layers around WR 140 and its companion than ever seen before, Han and another team report October 12 in Nature Astronomy.

At first glance, the intricate patterns surrounding the stars resemble a gigantic spiderweb. But the researchers’ analysis reveals that they are actually enormous, expanding, cone-shaped dust shells. They’re nested inside each other, with a new one forming every eight years as the stars complete another journey around their orbits. In the new images, the shells look like sections of rings because we observe them from the side, Han says.  

A computer simulation that takes radiation pressure from starlight into account shows how a dust plume (expanding arc and line) emerges from a pair of orbiting stars (not visible).Y. Han/Univ. of Cambridge

The patterns don’t completely surround the stars because the distance between the stars changes as they orbit one another. When the stars are far apart, the density of the colliding gas is too low to condense to dust — an effect the researchers expected. 

What surprised them is that the gas doesn’t condense well when the stars are closest together either. That suggests there’s a “Goldilocks zone” for dust formation: Dust forms only when the separation between the stars is just right, creating a series of concentric dust shells rippling away from the duo.

“Their Goldilocks zone is a new idea,” says astrophysicist Andy Pollock of the University of Sheffield in England, who was not part of either study. “A similar sort of thing happens in my field of X-rays.”

In his work, Pollock has observed that WR 140 and its partner emit more X-rays as the stars approach each other, but then fewer as they get very close together, suggesting there’s a Goldilocks zone for X-rays coming from the stars as well. “It would be interesting to see if there’s any connection” between the two types of Goldilocks zones, he says. “All of this must somehow fit together.” More

Roughly 3,000 light-years from Earth sits one of the most complex and least understood nebulae, a whirling landscape of gas and dust left in the wake of a star’s death throes. A new computer visualization reveals the 3-D structure of the Cat’s Eye nebula and hints at how not one, but a pair of dying stars sculpted its complexity.

The digital reconstruction, based on images from the Hubble Space Telescope, reveals two symmetric rings around the nebula’s edges. The rings were probably formed by a spinning jet of charged gas that was launched from two stars in the nebula’s center, Ryan Clairmont and colleagues report in the October Monthly Notices of the Royal Astronomical Society.

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“I realized there hasn’t been a comprehensive study of the structure of the nebula since the early ’90s,” says Clairmont, an undergraduate at Stanford University. Last year, while a high school student in San Diego, he reached out to a couple of astrophysicists at a scientific imaging company called Ilumbra who had written software to reconstruct the 3-D structure of astronomical objects.

The team combined Hubble images with ground-based observations of light in several wavelengths, which revealed the motions of the nebula’s gas. Figuring out which parts were moving toward and away from Earth helped reveal its 3-D structure.

The team identified two partial rings to either side of the nebula’s center. The rings’ symmetry and unfinished nature suggest they are the remains of a plasma jet launched from the heart of the nebula, then snuffed out before it could complete a full circle. Such jets are usually formed through an interaction between two stars orbiting one another, says Ilumbra partner Wolfgang Steffen, who is based in Kaiserslautern, Germany.

The work won Clairmont a prize at the 2021 International Science and Engineering Fair, an annual competition run by the Society for Science, which publishes Science News. Steffen was skeptical about the tight deadline — when Clairmont reached out, he had just two months to complete the project.

“I said that’s impossible! Not even Ph.D. students or anybody has tried that before,” Steffen says. “He did it brilliantly. He pulled it all off and more than we expected.” More

Some of the earliest stars yet seen are now coming to light in one of the first images from the James Webb Space Telescope.

Formed roughly 800 million years after the Big Bang, the stars live in dense groups called globular clusters and surround a distant galaxy dubbed the Sparkler,  astronomers report in the Oct. 1 Astrophysical Journal Letters. Globular clusters often host some of the oldest stars in contemporary galaxies such as our own, but it’s hard to tell their exact age. The new finding could help researchers pinpoint when such clusters began to form.

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Compared to a galaxy, globular clusters are tiny, which makes them hard to see from across the universe. But this time, a gargantuan natural lens in space helped. The Sparkler is one of thousands of galaxies that lie far behind a massive, much closer galaxy cluster called SMACS 0723, which was the subject of the first publicly released science image from the James Webb Space Telescope, or JWST (SN: 7/11/22). The cluster distorts spacetime such that the light from the more distant galaxies behind it is magnified.

For all those remote galaxies, that extra magnification brings out details that have never been seen before. One elongated galaxy surrounded by yellowish blobs got the attention of astronomer Lamiya Mowla and her colleagues.

“When we first saw it, we noticed all those little dots around it that we called ‘the sparkles,’” says Mowla, of the University of Toronto. The team wondered if the sparkles could be globular clusters, close-knit families of stars that are thought to have been born together and stay close to each other throughout their lives (SN: 10/15/20).

“The outstanding question that there still is, is how were the globular clusters themselves born?” Mowla says. Were they born at “cosmic noon,” 10 billion years ago, when star formation throughout the universe peaked? Or did they form 13 billion years ago at “cosmic dawn,” when stars were first able to form at all (SN: 3/4/22)?

Light from the Sparkler takes about 9 billion years to reach Earth, so if the sparkles are globular clusters that shone that long ago, they might help astronomers answer that question.

Zooming into one part of JWST’s image of the galaxy cluster SMACS 0723, astronomers zeroed in on the yellow dots around this one elongated background galaxy, which they called the Sparkler. Some of the dots may be globular clusters of same-age stars formed just a few hundred years after the Big Bang.L. Mowla et al/The Astrophysical Journal Letters 2022

Mowla and her colleagues used data from JWST to analyze the wavelengths of light coming from the sparkles. Some of them appear to be forming stars at the time when their light left the clusters. But some had formed all their stars long before.

“When we see them, the stars are already about 4 billion years old,” says astrophysicist Kartheik Iyer, also of the University of Toronto.

That means the oldest stars in the sparkles could have formed roughly 13 billion years ago. Since the universe is 13.8 billion years old, “there’s only a short amount of time after the Big Bang when these could have formed,” he says.

In other words, these clusters were born at dawn, not at noon.

Studying more globular clusters around ancient galaxies could help determine if such clusters are common or rare early on in the universe’s history. They could also help unravel galaxies’ formation histories, say Mowla and Iyer. Their team has proposed observations to be made in JWST’s first year that could do just that.

Being able to pick out tiny structures like globular clusters from so far away was almost impossible before JWST, says astronomer Adélaïde Claeyssens of Stockholm University. She was not involved in the new work but led a similar study earlier this year of multiple galaxies magnified by the SMACS 0723 cluster.

“It’s the first time we showed that, with James Webb, we will observe a lot of these type of galaxies with really tiny structures,” Claeyssens says. “James Webb will be a game changer for this field.” More