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Great Spitzer image: Organic molecules in the Pinwheel Galaxy July 25, 2008

Posted by Sarah in science.
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This picture was on the BBC news website today. It’s a fab picture taken in the infrared with the Spitzer Space Telescope, which operates in the infrared. The press release is here. There’s also quite an entertaining -albeit a bit cringeworthy- video on the Spitzer website at Caltech. Well done, Karl!

It shows how polycyclic aromatic hydrocarbons, or PAHs, become quite suddenly depleted towards the outer rim of the galaxy.

PAHs are complex carbon-containing molecules that are ubiquitous in the Universe, marking out regions where stars are being born. Although spiral galaxies like the Pinwheel are often hotbeds of ongoing star formation, the absence of PAH molecules would suggest that no new stars are being born in the outer ring of this galaxy.

It’s nice to see great mid-infrared images like this in the news to complement the wonderful optical and near-infrared images we get from Hubble and VLT. In my experience many astronomers find IR astronomy to be a slightly boring field as it deals with observations of molecules, dust, and generally cool things (in temperature). Observing in the mid-infrared from the ground is also much more challenging than at optical wavelengths given that (i) water molecules in the atmosphere absorbs many infrared wavelengths to we can only observe in certain windows; (ii) the atmosphere, the telescope, and all objects at circa-room temperature all actually emit infrared radiation that entirely drowns out the signal from a faint astronomical source.  A really good (but quite technical) overview of mid-IR observing issues is given by the Gemini Observatory here.

There are now some very good mid-IR instruments on ground-based telescopes, such as VISIR on VLT, Michelle on Gemini North, COMICS on Subaru. The results produced by these instruments will hopefully raise the profile of infrared astronomy!



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