Astronomers discover the first astrosphere around a sun-like star

BOSTON – For the first time, astronomers have discovered an astrosphere around a sun-like star.

This bubble of hot gas is blown by a star’s stellar wind, a continuous stream of charged particles that each star emits. The solar version of this bubble, called the heliosphere, marks the edge of our solar system and shields the planets from most of the high-energy cosmic rays orbiting the galaxy. (SN: 12/10/18, SN: 15/10/09).

Astronomers have seen similar bubbles around hot stars, dying stars, and small stars—but not sun-like stars.

“We don’t see them around … average, everyday stars that could host life,” astronomer Carey Lisse said at the 25 Years of Science with Chandra symposium on Dec. 3. “For 20 years, we’ve been looking for this effect. And we haven’t seen it.”

Lisse and his colleagues looked for a star that was blowing very strongly. The researchers targeted the Chandra X-ray Observatory in orbit around HD 61005, nicknamed The Moth because it is surrounded by a trailing disk of debris that resembles wings. Astronomers think the strange shape is because the star is plowing through a dense cloud of gas in space at a speed of about 10 kilometers per second. (SN: 1/22/08).

The moth has a similar size and mass to the sun, so “it’s a relatively good proxy for us,” said Lisse, of the Johns Hopkins Applied Physics Laboratory in Laurel, Md. But it is a comparatively young 100 million years. to the 4 billion year old sun. Younger stars tend to be more active and emit stronger solar winds than older ones. That extra activity, plus the star’s motion through the interstellar medium, led Lisse to think that Moth was a good target for detecting an astrosphere.

The observations showed that the mole is surrounded by a halo of X-ray light that extends 100 times farther from the star than Earth does from the sun. That light is the astrosphere, Lisse said.

Surprisingly, the bubble is round and not wing-shaped. This means that the wind is so strong that the dense cloud pushes the dense gas cloud outwards more than the cloud, like a thick balloon moving through thin air.

Studying the astrospheres of other sun-like stars can tell us what the sun was like in its youth, Lisse says. “We used to be like that,” he says. “The astrosphere is telling us about the history of the sun.”