Light can be thought as a collection of radiation of different wavelengths. Our eyes have evolved in such way that they are able to detect light of wavelengths within 390 and 700 nanometres (nm), wherein one nanometer corresponds to one meter divided into one billion equal parts. This is the so called visible light. The information carried on by this light are processed by our brains, and than we can interpret the world that we see. Besides visible light, radiation of many other wavelengths exist, which our eyes cannot detect, but instruments that we create can. Those radiation which are invisible for our eyes can still be very useful for a large range of human activities. For instance, X-ray (0.01nm – 10nm) is important in medicine, and microwaves (1 million nm – 1 billion nm) are important for heating up our food. These radiation are important in astronomy as well, since stars also emit different kinds of invisible radiation. Extremely valuable information about the Universe can be revealed by analyzing all kinds of radiation emitted by the astronomical objects. Here we are going to explore the so called infrared light – which wavelengths lay within the range between 700 nm and 1 million nm – and how it can help on the comprehension of the chemical properties of star forming regions.
Stars and their planetary systems born from the collapse of huge clouds, which are structures composed by dust and gas spread over the Galaxy. At some point, shock waves from the explosion of nearby old stars hit the clouds causing gravitational instabilities. Consequently, the clouds start to collapse. The utmost stage of the cloud collapsing process is the formation of planetary systems, just like our own Solar System. However, different stages take place between the starting collapse and the formation of a star and its planets. One of these stages is when the newborn star starts to shine its radiation, and is still surrounded by an envelope of dust and gas, as a remaining of the parental cloud. We know that when light crosses any material, it can be absorbed, scattered, or just pass through it. This depends on the nature of the material and the characteristics of the incident light, like the wavelength. So, visible light can hardly pass through this envelope, while infrared light can transpose this barrier more easily, being eventually detected by our telescopes later on. By analyzing this infrared light, astronomers can determine the chemical characteristics of these forming stars regions. Therefore, this is of ultimate importance on the comprehension of how planets, just like the Earth, are formed.
The dust present in this envelope is extremely tiny, composed of a nucleus of silicate material (similar to the grains from a sandy beach) covered by a mantle of frozen molecules, such as water (H2O), carbon monoxide (CO), and methanol (CH3OH). This mantle is the site where many different molecular species are formed. It is believed that even organic molecules important for life, such as amino acids – basis of proteins – are formed there. This material can be incorporated into the planets being formed around the young star. Therefore, this process of molecular formation can play an important role on the chance of life appearance in a planet. But how can we know which molecules are present in the mantle covering this dust?
One technique used by astronomers involves the analyses of the features present in the infrared light emitted by the newborn star. When infrared light crosses the surrounding envelope, it can be partially absorbed by the molecules present in the mantle covering the dust. Therefore, the light we detect with our telescopes brings information about which wavelength range was absorbed by the material composing the envelope. Since the absorption of specific wavelengths is caused by specific molecular species, these molecules can then be identified. Moreover, the dust is heated up when absorbing the radiation from the young star and then can also start to emit in infrared itself, revealing more information about its nature. That is how a chemical survey can be developed, enabling the characterization of the molecules present in the star forming regions. As an example to illustrate how diverse the chemistry of astronomical objects can be, using state-of-the-art telescopes, astronomers have recently reported the presence of methyl cyanide (CH3CN) – a complex carbon-based molecule containing carbon-nitrogen bounds – in the protoplanetary disc of a young star (1). This molecule presents essential characteristics for the formation of amino acids, the building blocks of life.
The Universe is full of secrets, and every day new exciting discoveries are made. This is an exciting era, since new powerful telescopes are being built, which will enable even more accurate study of astronomical light, promising to greatly enlarge our knowledge about the Universe in which we live.
1 – Complex Organic Molecules Discoverd in Infant Star system, 8 April 2015, eso 1513 – Science Release, http://www.eso.org/public/news/eso1513/
Eduardo Monfardini Penteado is currently a PhD in astrochemistry working at the Radboud University, Netherlands. His studies involve modelling the chemical evolution of molecular clouds, and the characterization of chemical properties of young stellar objects. Also interested in science outreach, is member of the GalileoMobile project, having participated in the recently BraBo expedition to the Amazon region.