Interactions with neutral hydrogen particles, coming from the interstellar medium, may be responsible for leaving the heliosphere (the bubble that surrounds the Solar System and protects it from energetic particles) with a shape similar to that of a croissant. This discovery was made by a team led by astrophysicist Merav Opher, from Boston University, who sought to understand the cosmic forces responsible for defining the shape of the heliosphere.
Understanding this structure and how it works is important for scientists to also understand our neighborhood and even the emergence of life on Earth. However, since we are inside the heliosphere, trying to figure out its shape is not an easy task—but neither is it impossible. With data from the Voyager and New Horizons missions, scientists discovered that it could be similar to the shape of a croissant.
However, it still remained to discover what was behind this structure. For this, the authors studied heliospheric jets, twin emissions released by the sun’s poles whose shape comes from the interaction of the solar magnetic field with the interstellar one. As a result, they are not emitted in a straight line, but curve like the ends of a croissant — these ends are also the “tails” of the Solar System.
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These emissions are similar to other astrophysical jets observed in space and, as with the others, the Sun’s jets are also unstable; consequently, the heliosphere, which is “drawn” by the Sun, also appears to be unstable. “We see these jets being designed as irregular columns, and astrophysicists have wondered for years why these shapes show instabilities,” explained Opher.
Thus, the team worked with computer models focused on neutral hydrogen atoms, that is, those without charge. The effects they have on the heliosphere are not yet known, but when the researchers removed these atoms from the model, the solar jets were stable; then the authors put them back and observed the instability returning to the jets.
According to the team’s analysis, this is due to the interaction of neutral hydrogen with ionized matter in the outer region of the heliosphere. As a result, this causes the so-called “Rayleigh-Taylor instability”, which occurs at the interface between two fluids of different densities: the lighter pushes the heavier one, which generates turbulence in the tails of the heliosphere.
This explanation may have implications for understanding how the galactic cosmic rays enter the Solar System, also helping to understand the environment outside the protection of the Earth’s magnetic field. “This is a huge discovery, which really puts us on the path to discovering why our heliosphere model achieves this unique croissant shape, and others don’t.”
The article with the results of the study was published in The Astrophysical Journal.
Source: Astrophysical Journal; Via: Science Alert, Boston University
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