BOSTON — For the first time, astronomers have detected an astrosphere around a star similar to our sun. This bubble of hot gas is created by a star's stellar wind, a continuous flow of charged particles emitted by every star. The sun's version of this bubble, known as the heliosphere, defines the boundary of our solar system and shields the planets from most of the high-energy cosmic rays that travel through the galaxy (SN: 12/10/18, SN: 10/15/09). Astronomers have observed similar bubbles around hot stars, dying stars, and young stars—but not around sun-like stars.
“We don’t see them around … average, everyday stars that might host life,” said astronomer Carey Lisse at the 25 Years of Science with Chandra symposium on December 3. “For 20 years, we’ve been looking for this effect, and haven’t seen it.” Lisse and his team targeted a star that was emitting unusually strong stellar winds. They used the orbiting Chandra X-Ray Observatory to observe HD 61005, nicknamed The Moth due to its swept-back debris disk resembling wings. Astronomers believe this unusual shape is caused by the star moving through a dense gas cloud at approximately 10 kilometers per second (SN: 1/22/08).
The Moth is similar in size and mass to the sun, making it a good representative of our star, according to Lisse of the Johns Hopkins Applied Physics Laboratory in Laurel, Md. However, The Moth is only 100 million years old compared to the sun's 4 billion years. Younger stars are generally more active and emit stronger solar winds than older ones. This increased activity, combined with the star's movement through the interstellar medium, led Lisse to believe The Moth was a promising candidate for detecting an astrosphere.
The observations revealed that The Moth is surrounded by a halo of X-ray light extending 100 times the distance from Earth to the sun. This light is the astrosphere, according to Lisse. Surprisingly, the bubble is round rather than wing-shaped, indicating that the stellar wind is so powerful that it pushes outward on the dense gas cloud more effectively than the cloud pushes back, similar to a thick balloon moving through thin air.
Studying the astrospheres of other sun-like stars can provide insights into what the sun was like in its early years, Lisse says. “We were like this once,” he notes. “The astrosphere is revealing information about the sun’s past.”
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