Oddball pair of stars producing dust shells like clockwork

On Oct 15, 2022

The James Webb Space Telescope has spotted an intriguing object created by a rare pair of stars that are encircled by rings of dust. The pair, known as Wolf-Rayet 140, is located 5,000 light-years away and could us learn about the interstellar medium between stars and how stars form.

This system consists of two stars, one older and massive of a type called a Wolf-Rayet star, and the other hot a blue-white type called an O-type star. And they orbit in such a way that they come close together once every eight years. When that happens, the stellar winds that each star gives off begin to interact. This interaction causes the large Wolf-Rayet star to shed some of its stellar material, which forms dust.

Shells of cosmic dust created by the interaction of binary stars appear like tree rings around Wolf-Rayet 140. The remarkable regularity of the shells’ spacing indicates that they form like clockwork during the stars’ eight-year orbit cycle, when the two members of the binary make their closest approach to one another. In this image, blue, green, and red were assigned to Webb’s Mid-Infrared Instrument (MIRI) data at 7.7, 15, and 21 microns (F770W, F1500W, and F2100W filters, respectively). NASA, ESA, CSA, STScI, NASA-JPL, Caltech

It is this formation of dust every eight years which creates the dust shells seen in the image above. Each interaction creates a new shell, and at least 17 of these shells are visible in the Webb data, showing over 130 years of history between the two stars.

“We’re looking at over a century of dust production from this system,” said lead author Ryan Lau, an astronomer at NSF’s NOIRLab, in a statement. “The image also illustrates just how sensitive this telescope is. Before, we were only able to see two dust rings, using ground-based telescopes. Now we see at least 17 of them.”

Webb was able to see the many shells using its Mid-Infrared instrument, which allowed the researchers to use different filters to see the chemical composition of the dust shells. They found they are made of compounds called Polycyclic Aromatic Hydrocarbons (PAHs), which are found in the space between stars — called the interstellar medium — and which play an important role in how stars form. There are only around 600 Wolf-Rayet stars known, but there could be evidence of many more in our galaxy.

“Even though Wolf-Rayet stars are rare in our galaxy because they are short-lived as far as stars go, it’s possible they’ve been producing lots of dust throughout the history of the galaxy before they explode and/or form black holes,” said co-author Patrick Morris of Caltech. “I think with NASA’s new space telescope we’re going to learn a lot more about how these stars shape the material between stars and trigger new star formation in galaxies.”

The research is published in the journal Nature Astronomy.

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