IBEX's Giant Interstellar "Ribbon" Explained


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A new study using data from NASA's Interstellar Boundary Explorer (IBEX) mission has put forth an explanation for an interstellar "ribbon" of energetic neutral atoms. The ribbon confounded researchers in 2009 when IBEX was able to map the interstellar boundary at the edge of our heliosphere, where particles from inside the solar system interact with and bounce off galactic material. Many more energetic particles were found to be streaming from the ribbon than in other places.

The new paper, published this week in The Astrophysical Journal, proposes that the ribbon is in an area where neutral hydrogen atoms from solar wind cross the galactic magnetic field, stripping away their electrons and changing them into charged ions. The particles then become trapped in the ribbon regions by vibrations in the magnetic field.

"Think of the ribbon as a harbor and the solar wind particles it contains as boats," says Nathan Schwadron, first author on the paper and researcher at The University of New Hampshire. “The boats can be trapped in the harbor if the ocean waves outside it are powerful enough. This is the nature of the new ribbon model. The ribbon is a region where particles, originally from the solar wind, become trapped or retained due to intense waves and vibrations in the magnetic field."

Previous models testing the magnetic field hypothesis had predicted a ribbon that was narrower than the one measured by IBEX. The new model fits with actual observations, and Schwadron stated that the math looks "remarkably like what the ribbon actually looks like."

“This is a perfect example of the scientific process," said David McComas, co-author of the paper and the principal investigator for the IBEX mission at the Southwest Research Institute. "We observe something completely new and unexpected with IBEX, develop various hypotheses to explain the observations, and then develop mathematical models to try to validate the hypotheses.”

The new hypothesis has yet to be confirmed, and changes in the ribbon in conjunction with solar wind will be observed to see if they match up with the new model. If correct, though, the findings could help researchers understand more about how the heliosphere interacts with the galaxy.

“The ribbon can be used to tell us how we’re moving through the magnetic fields of the interstellar medium and how those magnetic fields then influence our space environment,” said Schwadron.

(Image courtesy NASA/Goddard Space Flight Center Scientific Visualization Studio)