Is there anyone on Earth who doesn’t like croissants … those buttery, flaky pastries associated with France but actually invented in Austria? They’re so delicious, it wouldn’t be a chock if extraterrestrials visiting Earth enjoyed them too. Perhaps there’s an astronomical rather than gastronomical reason for their universal appear. It turns out the heliosphere of our solar system isn’t a sphere at all – new computer simulations show the protective bubble surrounding the Sun and its planets to deflect harmful galactic cosmic rays is shaped like a croissant. Wow – tasty and good for us too!
“Why do stars and black holes—and our own sun—eject unstable jets? We see these jets projecting as irregular columns, and [astrophysicists] have been wondering for years why these shapes present instabilities.”
Boston University astrophysicist Merav Opher and her team weren’t looking for galactic desserts when they formed SHIELD (Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics) – they were trying to figure out the size and shape of the heliosphere that forms a buffer zone protecting the solar system from cosmic radiation emitted from supernovas. They also hoped to see how the heliosphere interacts with the interstellar matter between stars, how cosmic rays get transported through the heliosphere, and why the heliosphere seems to be unstable.
“The universe is not quiet. Our BU model doesn’t try to cut out the chaos, which has allowed me to pinpoint the cause [of the heliosphere’s instability]…. The neutral hydrogen particles.”
In a BU press release announcing the publication of the group’s paper in The Astrophysical Journal, Opher explains the force that does the shaping of the heliosphere – the Rayleigh-Taylor instability which occurs when two materials of different densities collide. In this case, neutral hydrogen particles (neutrals) streaming in from outside our solar system are colliding with charged ions (pick-up ions) inside it. In a simple test, Opher removed the neutrals from the model and saw that the jets coming from the sun, which shaped the heliosphere from the inside, became super stable. This is called the Rayleigh-Taylor instability and was known to cause other strange astronomical shapes like the Horsehead Nebula.
“Because the pick-up ions dominate the thermodynamics, everything is very spherical. But because they leave the system very quickly beyond the termination shock, the whole heliosphere deflates."
Unlike the buttery croissants which puff up, the buffery heliospheric croissant deflates into its crescent shape, with folds and curves like the pastry. Knowing where those anomalies are in the croissant-shaped heliosphere will help protect astronauts and spaceships traveling through it – avoiding areas with weak cosmic ray protection.
Is anyone else hungry for some croissants?