Centaurus A

Charles asked about a photo taken at the Magellan telescope while I was there in my 2002 run. Well, this is it. Not very spectacular, that is. However, interesting enough to justify more than 20 days spent on a mountaintop in the Chilean desert fighting with broken software and hardware with an attitude.

The fact is, in many cases professional astronomical observations are not very pretty to look at. This happens for sure when taking spectra (dispersing the light from the telescope according to its “color”), but also when doing thermal infrared observations (as the one above). The photo shows the nucleus onf an active galaxy (Centaurus A, left) compared with a point-like star (gamma Draconis). The nucleus of the galaxy (at the center of which there is a black hole) appears more extended, being surrounded by a large cloud of dust. The dust is heated by the hard radiation coming from the black hole (mostly X-rays) and is thus visible in the thermal infrared. A simple image like this allows to do a lot of interesting science. The nucleus is totally invisible in visible light, because it is obscured by thick dust lanes (which are instead transparent in the infrared).

Ground based thermal infrared images are in general not very pretty, because they usually have a narrow field of view, and because only the brightest objects are bright enough to be visible from the ground (even with a 6.5m telescope). From space, of course, it is all another matter, as demonstrated by the camera IRAC of the Spitzer Space Telescope (the instrument for which I am now working), which is producing images that are really breathtaking.