Amazing shells around stars are caused by light accelerating dust

Back in August, we reported on a stunning image of the breathtaking WR140 binary star system taken by JWST. Astronomers have now published scientific results related to this incredible object – and many others.

By combining the latest space telescope and decades of observations from Earth, scientists have gained a better understanding of what these shells are, how they are produced, and the role starlight plays in sculpting them.

WR140 consists of two stars: one is a Wolf-Rayet (which gives the system its name) 20 times the mass of our Sun; The second is a bright hot star still burning hydrogen, with a mass of 50 suns. They orbit each other every 7.93 years. When they approach each other, their stellar winds interact, creating shells of dust.

Using Keck Observatory data from 2001 to 2017, the researchers measured the movement of these shells with extraordinary precision. The interaction of winds occurs on the surface of a cone-shaped shock front, where dust is created. Then the movement of the stars spreads it out. Finally, their starlight accelerates this dusty shell outward.

“It is difficult to see starlight causing acceleration because the force weakens with distance and other forces quickly take over,” said lead author of the paper Keck Yinuo Han of the Cambridge Institute of Astronomy. “To observe acceleration at the level that becomes measurable, the material must be close enough to the star, or the source of the radiation pressure must be extremely strong. WR140 is a binary star whose wild radiation field supercharges these effects, placing them within striking distance of our high-precision data.”

Acceleration is a key discovery in this research. Before, the researchers expected that the movement of outflows would occur at a constant speed. Instead, the long data collection allowed scientists to measure it precisely and see that the shells were accelerating.

“In a sense, we’ve always known this must be the reason for the outflow, but I never dreamed we could see the physics working like this,” said co-author Professor Peter Tuthill from the University of Sydney. “When I look at the data now, I see the plume of the WR140 unfolding a giant sail made of dust. When it catches the photon wind rushing from the star, like a yacht catching a gust, it makes a sudden leap forward.”

However, that is not all, as JWST has allowed an even deeper look into the shells better than any instrument before. The researchers could track at least 17 shells, suggesting that this process has been going on for at least 130 years. They found that the shells are rich in carbonate dust grains. This suggests that Wolf-Rayet binaries can “contaminate” the interstellar medium with organic compounds.

“We will now be able to make observations like this much more easily than from the ground, opening a new window into the world of Wolf-Rayet physics,” added Ryan Lau who led the JWST study.

Keck’s observations were published in the journal Nature, while JWST is available in Nature Astronomy.

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