Astronomy: Astrosphere of a Sun-like Star Mapped for the First Time
A steady stream of particles forms a huge bubble around the Sun. Now, such a structure has been found around a Sun-like star for the first time.
(Image: X-ray: NASA/CXC/Johns Hopkins Univ./C.M. Lisse et al.; Infrared: NASA/ESA/STIS; Optical: NSF/NoirLab/CTIO/DECaPS2; Image Processing: NASA/CXC/SAO/N. Wolk)
A research group has succeeded for the first time in directly imaging the so-called astrosphere of a Sun-like star. This is the bubble-shaped structure that a star's continuous stream of particles blows into space, and which is called the heliosphere in our solar system. Hot gas particles of the solar wind dominate within the bubble; it ends where the colder interstellar gas takes over. While such structures have been observed around other stars, they have not been seen around stars as similar to our Sun as HD 61005. It is much younger, at only about 100 million years old: its stellar wind is 3 times faster and 25 times denser than that of our Sun. Therefore, the observations also offer a glimpse into the early history of our Sun. The astrosphere was detected with NASA's Chandra space telescope.
Much denser environment
This was achieved with the X-ray telescope because the bubble produces X-ray radiation where the stellar wind meets interstellar dust and gas, explains the research group. In addition, the stellar wind of HD 61005 is much stronger and more intense than that of the Sun. This enhances the bubble formation process, similar to what happened with the Sun several billion years ago. However, because the star is traveling in a completely different environment, its astrosphere has a diameter of about 200 astronomical units, which is about the same as our Sun's. Its heliosphere would only reach as far as Saturn in that location, explains study leader Carey Lisse from Johns Hopkins University: HD 61005's astrosphere would be ten times larger than the Sun's if it were here.
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In the solar system, the heliosphere and especially its extent are not easy to explore. Until a few years ago, no measurements could be taken outside of it at all; now, two devices, the space probes Voyager 1 and 2, are capable of doing so. Among other things, they determined that the boundary appears surprisingly sharp. Both space probes crossed the boundary of the heliosphere at almost the same distance: Voyager 1 in 2012 at a distance of about 121 astronomical units (one astronomical unit is the distance from the Earth to the Sun), Voyager 2 in 2018 at a distance of about 119 AU. HD 61005 could now provide new insights, as the star system was nicknamed "Moth" due to its shape. It is visible with binoculars.
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