Two rare stars whipping around each other in a wide, wild tango have given astronomers a unique opportunity to study the soft slapping of light against their dusty skirts.
The binary object called WR 140 is surrounded by a series of interlocking shells of dust that are slowly being pushed through space, not only by the binary stellar winds of charged particles, but by the glow of radiation emitted by the stars themselves. same.
For the first time, scientists were able to directly observe this radiation pressure in action, using infrared observations from the Keck Observatory to track a giant plume as it stretched through space over a period of 16 year.
This helps explain what we see in a recent image from the James Webb Space Telescope (JWST), the subject of a second article, showing the blazing binary nestled amid a profusion of glowing dust shells.
“It’s hard to see starlight causing acceleration because the force fades with distance and other forces quickly take over,” says astronomer Yinuo Han from the University of Cambridge.
“To witness an acceleration to the level where it becomes measurable, the material must be reasonably close to the star or the source of the radiation pressure must be very strong. WR 140 is a binary star whose fierce radiation field supercharges these effects, placing within reach of our high-precision data.”
WR 140 is located about 5,600 light-years away in the constellation Cygnus, and it’s a rarity among rarities. It’s called a colliding binary wind, made up of an extremely rare Wolf-Rayet star and a blue O-type supergiant star – another rare object.
As we explained earlier, Wolf-Rayet stars are very hot, very bright, and very old, igniting at the end of their main-sequence lifetime. They are significantly depleted in hydrogen, rich in nitrogen or carbon, and lose mass at a very high rate. This lost mass is also rich in carbon, which absorbs radiation from the stars and re-emits it as infrared light.
O-type stars, on the other hand, are among the most massive stars known, also very hot and bright; because they are so massive, their lifespan is incredibly short, dying out after only a few million years.
Both stars in the WR 140 system have fast stellar winds, blowing through space at around 3,000 kilometers (1,864 miles) per second. So both are losing mass at a pretty breakneck pace. It’s actually quite normal. But stars orbit each other in an elliptical or oval shape, which means they don’t orbit evenly. They approach to get closer (periaster) then move away again at a great distance (apastron).
At periapsis, their powerful stellar winds collide, creating shocks and a giant puff of dust that expands outward, creating a shell of dust. Stars orbit once every 7.94 years, which means that each new shell is created 7.94 years after the last. This predictability means that objects like WR 140 are fascinating objects for studying dust production and acceleration.
But you may have noticed that the shape of the shells is peculiar, with an elongated side, producing what has been described as a “circle” shape. It’s hard to explain from the stellar winds alone.
“In the absence of external forces, each spiral of dust should expand at a constant rate,” says Han.
“We were puzzled at first because we couldn’t match our model to the observations, until we finally realized we were seeing something new. The data didn’t match because the rate of expansion didn’t was not constant, but rather that it was accelerating. We had filmed this for the first time on camera.”
But there is another explanation: radiation pressure. Electromagnetic radiation – light – exerts a tiny amount of pressure on whatever it hits, due to the momentum transfer from the photon to the surface. Photons are so small and massless that it won’t affect your daily life, but stars emit a lot of powerful radiation. Unfiltered and in the vacuum of space, it can actually grow matter. This is the principle of lightsail technology.
When the team included radiation pressure in their models of WR 140, they were able to reproduce the peculiar shape of the swelling shells around the binary.
“In a way, we always knew that had to be the reason for the outflow, but I never imagined we could see physics at work like this,” says astrophysicist Peter Tuthill of the University of Sydney in Australia.
“When I look at the data now, I see the WR140 plume unfurling like a giant sail made of dust. When it picks up the wind of photons from the star, like a yacht picking up a gust, it leaps into before suddenly.”
The Universe is, truly, full of wonders.
The team’s research has been published in Natureand the second article on the JWST observations in natural astronomy.
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