Interstellar dust plumes observed in intense starlight

plumes of debris have been observed being ‘pushed’ into interstellar space by intense starlight using NASA’s James Webb Space Telescope

The results of the intense starlight came from using infrared images of the binary star system WR140 taken over 16 years. In a complementary study of WR140, NASA’s James Webb Space Telescope (JWST) was able to see much deeper to snap an image of not just a single accelerating dust plume, but almost 20 of them, nested inside each other like a giant set of onion skins.

WR140 is comprised of a huge Wolf-Rayet star and an even bigger blue supergiant star, gravitationally bound in an interstellar eight-year orbit.

This binary star, in the Cygnus constellation, has been monitored for two decades with one of the world’s largest optical telescopes at the Keck Observatory in Hawai’i.

WR140 episodically puffs out plumes of dust stretching thousands of times the distance from the Earth to the sun. These dust plumes, produced every eight years, give astronomers a unique opportunity to observe how starlight can affect matter in an interstellar situation such as this.

rarely witnessed

It’s known that light carries momentum, exerting a push on matter known as radiation pressure.

Astronomers often witness the outcome of this phenomenon in the form of matter coasting at high speed around the cosmos, but it’s been a difficult process to catch in the act.

Direct recording of acceleration due to forces other than gravity is rarely witnessed, and never in an intense starlight environment like this.

Yinuo Han, from the University of Cambridge’s Institute of Astronomy, and first author on the paper, said: “It’s hard to see starlight causing acceleration because the force fades with distance, and other forces quickly take over.

“To witness acceleration at the level that it becomes measurable, the material needs to be reasonably close to the star or the source of the radiation pressure needs to be extra strong.

“WR140 is a binary star whose ferocious radiation field supercharges these effects, placing them within reach of our high-precision data.”

All stars generate stellar winds, but those from Wolf-Rayet stars can be more like a stellar hurricane. Elements such as carbon in the wind condense out as soot, which remains hot enough to glow bright in the infrared. Like smoke in the wind, this gives telescopes something that can be observed.

interstellar shock front

Han and his team found that the dust does not stream out from the star with the wind in a hazy ball. Instead, the dust forms where the winds from the two stars collide, on the surface of a cone-shaped interstellar shock front between them.

Because the orbiting binary star is in constant motion, the shock front also rotates. The sooty plume gets wrapped into a spiral, in the same way that droplets form a spiral in a garden sprinkler.

The researchers found that WR140 has other tricks up its sleeve. The two stars are not on circular but rather elliptical orbits, and dust production turns on and off as the binary nears and departs the point of closest approach.

By modelling these effects into the three-dimensional geometry of the dust plume, the astronomers were able to measure to location of dust features in three-dimensional space.

“Like clockwork, this star puffs out sculpted smoke rings every eight years, with all this wonderful physics written then inflated in the wind like a banner for us to read,” said co-author Professor Peter Tuthill from the University of Sydney.

“Eight years later as the binary returns in its orbit, another appears the same as the one before, streaming out into space inside the bubble of the previous one, like a set of giant nested Russian dolls.”

The findings are reported in Nature.

Image: Astronomers have observed directly for the first time how intense light from stars can ‘push’ matter. Researchers from the universities of Cambridge and Sydney made the observation when tracking a giant plume of dust generated by the violent interactions between two massive stars.