NASA's Hubble Space Telescope (HST) captured this image of what appears to be a fast bow shock around a very young star in the Great Nebula in Orion. New research predicts a comparable slow bow shock ahead of the sun’s heliosphere. (Credit: NASA/Hubble Heritage Team) Enlarge

July 18, 2013 — A new study co-authored by Boston University astronomers indicates that a bow shock (a dynamic boundary between sun's heliosphere and the interstellar medium) is highly likely. These findings challenge recent predictions that no such bow shock would be encountered.

The researchers base their expectation of finding a bow shock on a new magneto-hydrodynamic simulation that confirmed a theoretically expected slow bow shock (SBS) ahead of the heliosphere. The new research supports the idea that the sun, like a boat moving through water, forms a crescent-shaped shockwave as it moves through interstellar gas. The study was published recently in the journal Geophysical Research Letters.

In the current study, Bertalan Zieger, lead author and research scientist at BU's Center for Space Physics, and colleagues predict that a slow bow shock should exist ahead of the heliosphere. This challenges some recent models that argued no bow shock at all would be found. Those studies, which used the Interstellar Boundary Explorer (IBEX) satellite to measure the speed of interstellar particles entering the solar system near the edge of the heliosphere, suggested that the sun was moving too slowly through interstellar space (at 52,000 miles an hour) to create a bow shock.

However, the bow shock that they refer to is what is called a fast bow shock. The new study shows that a slow type is possible: IBEX observations also indicate that the interstellar wind is slower than the fast and the intermediate wave, but faster than the slow wave. Using these observations, the researchers conducted a magneto-hydrodynamic simulation that predicts a slow bow shock should exist in front of the heliosphere.

More of the story, click image