Oz stargazers serve up interstellar noodles

Dark plasma lenses or divine appendages?

Stargazers from Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) have recorded the effect of interstellar gas "lenses", which interfere with quasar radio wave emissions.

Described as dark "'lumps' in the thin gas that lies between the stars in our galaxy", these structures were first hinted at 30 years ago, when astronomers noticed radio waves from a quasar "varying wildly in strength".

Although they were able to deduce that the effect was caused by concentrations of charged particles in the thin interstellar atmosphere, scientists subsequently found these "extreme scattering events" (ESE) extremely elusive.

Now, though, CSIRO's Dr Keith Bannister and colleagues have used the Australia Telescope Compact Array to view an ESE in real time.

The team scanned roughly 1,000 active galactic nuclei for radio wave fluctuations, finally pinpointing a year-long ESE involving quasar PKS 1939–315 in the constellation of Sagittarius.

While observing the ESE, the astronomers noted no variation in the optical output of PKS 1939–315 - a significant fact because it means "earlier optical surveys that looked for dark lumps in space couldn’t have found the one his team has detected", according to Bannister.

The questions as to how the lenses form and just what shape they are remain to be answered. The former could be explained by cold clouds of gas held together by gravity.

Regarding the latter, the scientists have apparently discounted a solid lump or bent sheet structure. CSIRO team member Dr Cormac Reynolds said: "We could be looking at a flat sheet, edge on, or we might be looking down the barrel of a hollow cylinder like a noodle, or at a spherical shell like a hazelnut."

Further observations will "definitely sort out the geometry", Reynolds concluded.

The CSIRO research is published in Science. ®

Bootnote

Thanks to colander-wearing reader Rich Puhek for the heads-up.


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