A Breakthrough Study Reveals How Our Sun's Heliosphere Is Shaped by the Universe

We live in a croissant-shaped heliosphere.
Loukia Papadopoulos

In March of 2020, we brought you the news that physicists had unveiled an advanced new model of the heliosphere — the vast volume of space surrounding the Sun reaching more than twice the distance of Pluto — and it showed a crescent-shaped magnetic force-field in the shape of a freshly-baked croissant. Now the same physicists have discovered why our heliosphere is of this particular shape.

The discovery was led by Boston University astrophysicist Merav Opher and University of Maryland astrophysicist James Drake.

“How is this relevant for society? The bubble that surrounds us, produced by the sun, offers protection from galactic cosmic rays, and the shape of it can affect how those rays get into the heliosphere,” said in a statement, Drake. “There are lots of theories but, of course, the way that galactic cosmic rays can get in can be impacted by the structure of the heliosphere—does it have wrinkles and folds and that sort of thing?”

A representative of Boston University told IE in an email that Opher and Drake used computational modeling to test their theory that neutral hydrogen particles streaming from outside our solar system are what make it impossible for the heliosphere to flow uniformly. While seeking to prove that concept, they further found that the presence of the neutrals colliding with the heliosphere triggers a phenomenon called the Rayleigh-Taylor instability.

This process well known by physicists occurs when two materials of different densities collide. As the lighter material pushes against the heavier material, crazy irregular shapes are formed. In our Sun's heliosphere, the physicists found that the drag between the neutrals and ions generates its much-discussed croissant shape. 

Drawing this conclusion was no smaller feat. Opher had to recruit experts from 11 other universities and research institutes in an effort the team calls SHIELD (Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics). In the end, it seems to have been worth it.

The study was published this week in The Astrophysical Journal.

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