Ribbon in the Sky

Remember IBEX? NASA’s Interstellar Boundary Explorer has been mapping the outer limits of the solar system from a highly eccentric Earth orbit for almost a year now. It was designed to observe the Sun’s heliosphere — the bubble blown in the interstellar medium by the solar wind. What it found was such a surprise that it’s left theoreticians and solar physicists a bit bewildered.

Seeing as interesting things happen when stellar material hits the interstellar medium, I’d been really looking forward to seeing what IBEX discovered, but this is a total curve ball. IBEX works by looking for energetic neutral atoms (or ENAs for short). These energetic atoms are created as the solar wind crashes into the interstellar medium. This scatters atoms in all directions, including a few which are scattered back at us. The actual number of atoms detected by IBEX is tiny, but it’s detectors are sensitive enough to pick them up. Everyone was expecting there to be more of these atoms coming from one direction — the previous idea was that as the Sun travels through the galaxy, most interstellar particles would strike one side. Its heliosphere would be drawn into a comet-like shape.

What IBEX saw was that wonky L-shaped thing in the image. It shows a region with a high concentration of charged particles, but what precisely causes this is a mystery. Abashedly, everyone’s had to admit that they don’t really know what’s going on. This phenomenon certainly doesn’t fit with any of the previous models or ideas about how the heliosphere works.

David McComas, principal investigator for IBEX suggests a fascinating explanation for this. This ribbon could actually be caused by interstellar magnetic fields! Looking at the image, this seems logical. The curved shape seen does look somewhat reminiscent of the ribbon-like aurora borealis seen on Earth. Reminiscent, but much much larger. I’m not an expert in this, but I suspect that magnetic fields at a galactic scale are poorly understood. More often than not, they simply seem to go unmentioned. On seeing such a dramatic example, I can’t help but wonder what effects such a vast magnetic field might have on interstellar physics.

To read more, full results were published in Science this week.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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