Ultraviolet spectroscopy and photodesorption of interstellar ice
30-01-2014. CAB THESIS

Gustavo Adolfo Cruz Díaz defended his thesis work at the Autonomous University of Madrid entitled " Ultraviolet spectroscopy and photodesorption of interstellar ice " directed by Guillermo Muñoz Caro obtaining the qualification of Outstanding " Cum Laude ".

There are dark areas in the night sky where stars are very difficult to see. These areas are known as molecular clouds in interstellar space, large reserves of gas and dust, in which new stars are formed. They are composed primarily of molecular hydrogen, 10% helium and traces of heavier species. They have a visual extinction ranging from 1 to 10 mag, have temperatures of 10 to 20 K and usually have an irregular structure in lumps. Molecular clouds are optically opaque, which means that light from outside is absorbed in the cloud's boundaries. This is where the interstellar ice is formed.

The interstellar ice is a layer of molecules on the surface of dust grains. Due to the low temperatures inside the clouds, the chemistry is given by reactions on the surface responsible for the formation of H 2 and H 2 O among other species , or by means of cosmic rays. These have enough energy to penetrate into the clouds, excite the hydrogen molecules and generate a field of ultraviolet photons that process the mantles generating new molecular species.

One way to study these phenomena is by means of spectroscopic observations, in the infrared range, of the sky. But there is also laboratory astrophysics that allows us to compare observations with simulations in controlled environments. For this, an ultra high vacuum chamber and a cryostat are used to recreate the pressures and temperatures of the molecular clouds. The ice sheets are irradiated with a vacuum ultraviolet lamp, which reproduces the ultraviolet field inside the cloud. The solid and gaseous phases are monitored by means of infrared spectroscopy and mass spectrometry within the chamber.

Using laboratory tools, astronomical observations and computer models we can obtain a broad view of what is the transformation of simple species such as H 2 O, CO, CO 2 , CH 4 , etc. in more complex molecules like the amino acids present in organic beings.


Fuente: UCC-CAB


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