Astronomers using the James Webb Space Telescope have discovered two stars responsible for the formation of carbon-rich dust just 5000 light-years from the Sun in our Milky Way galaxy.
The massive stars in Wolf-Rayet 140 fly past each other in their elongated orbits. For a few months every eight years, the stars form a new dust envelope that expands outward – and may eventually become part of stars forming in other parts of our galaxy.
The formation of envelopes
Astronomers have long tried to track how elements such as carbon, essential for life, are distributed in the universe. Now, the James Webb Space Telescope has taken a closer look at one of the current sources of carbon-rich dust in our own Milky Way galaxy: Wolf-Rayet 140, a system of two massive stars moving in a tight, elongated orbit.
As they fly past each other (within the central white dot in Webb’s images), the stellar winds from each star compress, material is compressed, and carbon-rich dust is formed. Webb’s latest observations show 17 dust envelopes glowing in mid-infrared light that regularly expand into the surrounding space.
“The telescope confirmed that these dust envelopes exist, and its data also showed that the dust envelopes are moving outward at a constant rate, exhibiting visible changes in incredibly short periods of time,” said Emma Lieb, lead author of the new paper and a doctoral student at the University of Denver in Colorado.
Credit:
NASA, ESA, CSA, STScI, E. Lieb (University of Denver), R. Lau (NSF NOIRLab), J. Hoffman (University of Denver)
Incredible speed
Each shell is hurtling away from the stars at more than 2,600 kilometers per second, which is almost 1% of the speed of light.
“We used to think of events in space as happening slowly, over millions or billions of years,” added Jennifer Hoffman, co-author of the paper and a professor at the University of Denver, “In this system, the observatory shows that the dust envelopes are expanding year after year.
“Seeing the movement of these shells in real time between Webb’s observations, which were taken only 13 months apart, is really remarkable,” says Olivia Jones, co-author from the British Astronomy Technology Center in Edinburgh, “These new results give us our first insight into the potential role of massive binary objects like dust factories in the Universe.
Like clockwork, stellar winds generate dust for a few months every eight years when a pair makes a close approach during a wide, elongated orbit. Webb also shows where the dust formation stops – look for the darker area in the upper left of both images.
Older shells
The telescope’s mid-infrared images have revealed envelopes that have persisted for more than 130 years (older envelopes have scattered so much that they are now too dim to be detected). The researchers suggest that stars will eventually generate tens of thousands of dust envelopes over hundreds of thousands of years.
“Mid-infrared observations are crucial for this analysis because the dust in this system is quite cold. Observations in the near-infrared and visible would only show the envelopes that are closest to the star,” explained Ryan Lau, co-author and astronomer at the NSF NOIRLab in Tucson, Arizona, who led the initial studies of this system. “With these incredible new details, the telescope also allows us to study when exactly the stars form dust – almost to the day.
The distribution of dust is uneven. Although these differences are not apparent in Webb’s images, the team found that some of the dust has “clumped” together to form amorphous, fragile clouds that are the size of our entire solar system. Many other individual dust particles float freely. Each speck of dust is about one hundredth the width of a human hair. Lumpy or not, all dust moves at the same speed and is rich in carbon.
The future of the Wolf-Rayet 140 system
What will happen to these stars in millions or billions of years when they finish “spraying” their surroundings with dust? The Wolf-Rayet star in this system is 10 times more massive than the Sun and is approaching the end of its life. In its final “act,” this star will either explode as a supernova – possibly tearing through part or all of its dust envelope – or collapse into a black hole that leaves the dust envelope intact.
While no one can predict with certainty what will happen, researchers are rooting for the black hole scenario.
“The big question in astronomy is where does all the dust in the universe come from?” said Lau. – “If this carbon-rich dust survives, it could help us begin to answer that question.
“We know that carbon is essential for the formation of rocky planets and solar systems like ours,” Hoffman adds. – “It’s fascinating to see how binary star systems not only create carbon-rich dust, but also propel it into our galactic environment.
These results were published in Astrophysical Journal Letters and presented at a press conference at the 245th meeting of the American Astronomical Society.
