Chandra Captures First X-ray Image of Astrosphere Around Sun-like Star HD 61005

Astronomers have obtained the first clear X-ray image of an astrosphere, a large, wind-generated bubble, surrounding the Sun-like star HD 61005. This achievement, documented in a study published in the Astrophysical Journal, utilized NASA's Chandra X-ray Observatory to visualize the structure enveloping the star, which is located about 120 light-years away in the constellation Puppis.

The star HD 61005, classified as a G8 Vk yellow dwarf with solar metallicity, shares a comparable mass and temperature with our Sun, yet it is significantly younger, estimated at only 100 million years compared to the Sun’s 5 billion years. This immaturity results in a stellar wind that is substantially more energetic, traveling approximately three times faster and possessing a density about 25 times greater than the current solar wind. The detected astrosphere is a cavity of superheated gas formed where this powerful stellar wind collides with cooler, ambient interstellar gas and dust, mirroring the heliosphere that shields our Solar System from galactic cosmic radiation.

This direct X-ray imaging marks the first time such a structure has been observed around a solar-type star, providing a tangible model of the Sun's heliosphere during its own early, turbulent phase. The X-rays defining the bubble originate precisely at the collision boundary between the high-velocity stellar outflow and the interstellar medium. The structure's diameter spans an impressive 200 times the Earth-Sun separation distance. HD 61005 is informally known as "Moth" due to the wing-like shape of its debris disk, which is analogous to the Kuiper Belt in our Solar System.

The X-ray detection was facilitated by the star's current trajectory through a region of space where the surrounding interstellar medium density is estimated to be one thousand times greater than the density in the Sun's present galactic neighborhood, which amplified the interaction. Initial X-ray emission data were gathered during a one-hour observation by Chandra in 2014, but definitive confirmation of the extended structure required a nearly 19-hour observation period in 2021. The research initiative was directed by Carey Lisse of Johns Hopkins University.

This observational breakthrough offers an external, direct perspective on the architecture of a Sun-like star's protective bubble. Co-author Scott Wolk of the Center for Astrophysics | Harvard & Smithsonian noted that this image informs the understanding of the Sun's early wind and its potential impact on the initial conditions of the Solar System. Furthermore, the density contrast implies that if the Sun were in the Moth's current location, its heliosphere would shrink to extend only to Saturn's orbit. The investigation, which also used Hubble Space Telescope infrared data to visualize the 'wings,' underscores the dynamic interplay between stellar evolution and the surrounding galactic medium, including the illustration of a bow shock caused by the system moving through the interstellar gas at supersonic speeds.