03/07/2018

Have you ever wondered what the Universe is made of?

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Reproduction from the IMPA Science & Mathematics blog, published in O Globo, and coordinated by Claudio Landim.

Alan Alves Brito, Federal University of Rio Grande do Sul (UFRGS) and Brazilian Astronomical Society (SAB)

Have you ever wondered what the Universe is made of? This question has been part of the history of science and human thought for centuries. Currently, scientists working in Physics, Astrophysics, and Cosmology are desperately trying to understand what 95% of the Universe is made of, a fraction divided between dark matter (27%) and dark energy (68%), which, although sharing the same name, "dark," have distinct physical natures. Only 5% of the Universe is what we can see and detect. This tiny portion of what we know is described by the chemical elements of the periodic table, which are the basic ingredients of matter and everything we can observe in nature today. But what is the origin of these elements?

Hydrogen and helium are the most abundant elements, formed in the first 3 minutes after the Big Bang, which marks the beginning of everything that exists. Oxygen is the third most abundant chemical element, followed by carbon, which is the basis of life as we know it today. The oxygen we breathe, the nitrogen in the atmosphere, the iron in our blood, the calcium in our bones, the silicon in our computers, and the fluoride in toothpaste—all these elements are formed inside stars of different masses. The most massive stars, above 8 times the mass of the Sun, can produce chemical elements as heavy as iron in their core. Natural elements heavier than iron, for example, barium, lanthanum, yttrium, zirconium, and europium, are produced by other processes in various astrophysical environments. Depending on their initial mass, stars will live and die in different ways (see here for more details).

Our Sun formed approximately 4.5 billion years ago from a gaseous nebula (molecular cloud) composed mostly (98%) of hydrogen and helium; metals (all chemical elements heavier than helium) contributed 2%. These metals were produced by stars that were born and died before the Sun. Despite their small contribution, metals are responsible for the distinct chemical composition of the planets in the Solar System and, more importantly, for the production of chemical elements and molecules that will give rise to and sustain life on Earth.

Theory, experimentation, and observation go hand in hand on this journey of scientific knowledge. Although scientists have already managed to unravel many of the secrets about the processes of formation of chemical elements in nature, there are still various questions waiting for answers: what are the details of the physical processes that produce chemical elements and in which astrophysical environments? What is the chemical composition of the Universe and how does it influence the formation of stars and planets? Is there any connection between the chemistry of stars and that of the planets they host? What is the chemical composition of the more than 3,000 new planets now known outside the Solar System? What else does Quantum Mechanics, that is, the part of Physics that deals with atoms and the world of the very small, hold for us in understanding the chemical elements of the periodic table?

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