Massimo's photoblog

Epsilon Eridani (Jan 9, 2004)

This is an image from the poster I presented at the Conference I am presently in. It features the bright nearby star epsilon Eridani (distant 10 light years from us), taken in the thermal infrared with the camera IRAC on the Spitzer Space Telescope. Stars do not have spikes, but they do show up in astronomical images as having a lot of structures because of the nature of optical telescopes and the imperfections of the optics and the detectors. Brighter the star and brighter are all these structures. The orange and red “cross” is due to electronic artifacts caused by the detector (a 256x256 = 0.07Mpixel detector costing hundred of thousands of dollars), while the blue and green spikes are the result of the diffraction of the star light through the telescope optics.

The little colored dots are stars and galaxies in the background (these stars are what I am interested in). Epsilon Eridani is a relatively young star (730 million years of age, to compare with the 4.5 billion years age of the Sun), and is surrounded by a “debris disk” made with the leftover dust and rocks from the formation of its own planetary system. This disk has been detected at radio frequencies, and shows asymmetries that may be due to the perturbative effects of planets or other unseen companions of substellar mass. By imaging the star in the thermal infrared (where low mass objects are brighter compared to their parent star) I am trying to discover these bodies. It is however a very though job, because the light from the central star almost completely overexposes the image, and should be treated with very difficult techniques. Once the light of the bright star is removed, I can identify the nature of the remaining specks of light in the image on the base of their color (for example, the red fuzzy dots are background spiral galaxies, whose red color is due to the emission of special organic molecules whose stellar forming regions are generally rich).

Note that the color rendering in the image is somewhat artificial: as I said the image above is taken in the thermal infrared, at a wavelength at which the human eye is not sensitive (we only feel thermal infrared as radiating heat - yes, modern astronomical cameras can feel the heat produced by a galaxy millions of light years away), and is translated into the regular visible rainbow of colors for convenience. This image would be impossible to make from the ground, because thermal infrared is almost completely absorbed by the water vapor in the atmosphere. For this reason I used an infrared camera onboard a cryogenically cooled spacecraft orbiting the Sun in a Earth trailing orbit, which is now almost 10 million kilometers from Earth.