The Origin of the Elements

The speaker introduces Ed Murphy, an astronomy professor from UVA, who is also in charge of night events at the McCormick Observatory. Ed Murphy expresses gratitude towards JLab for their commitment to science education and outreach. The talk focuses on the origin of elements, specifically gold and mercury, and how everything around us is made of atoms. The discussion delves into the composition of the human body, revealing that most of it is made up of oxygen, contrary to the common belief of being mostly hydrogen due to the prevalence of water in our bodies.

Astronomers have the ability to determine the composition of objects in space, even those never visited or unlikely to be visited by humans. By analyzing the light from stars, astronomers can discern what these celestial bodies are made of. The composition of distant stars is found to be similar to that of our sun, primarily consisting of hydrogen and helium. The process of breaking down light into its component colors, known as spectroscopy, is crucial in understanding the makeup of both our sun and distant stars. The talk also mentions various telescopes, including the Large Binocular Telescope and the Hubble Space Telescope, which aid in astronomical observations.

The periodic table of elements encompasses all elements that make up matter in the universe. There is nothing that exists made of matter not found on the periodic table. Each element's atomic number corresponds to the number of protons in its nucleus, and there are no missing numbers on the periodic table, indicating that every possible element has been discovered. The talk also touches on the history of the periodic table, highlighting Mendeleev's initial version with question marks indicating undiscovered elements. It is noted that all elements heavier than iron are artificially created in laboratories and are extremely unstable, decaying within seconds.

The origin of matter dates back to the Big Bang, where high-energy gamma rays collided to create matter and anti-matter. The difference between matter and anti-matter lies in their charges. However, during the early universe, a phenomenon occurred where matter was created without corresponding anti-matter, leading to the predominance of matter in the universe. This asymmetry between matter and anti-matter is a mystery in physics, and its resolution would be a monumental discovery. The Big Bang theory is not just a hypothesis; it can be tested in laboratories, such as at CERN, where conditions similar to those after the Big Bang can be recreated.

In the first minutes after the Big Bang, the universe was hot enough for nuclear reactions to occur, leading to the formation of hydrogen, helium, and trace amounts of lithium. However, the universe cooled rapidly, halting nuclear reactions after only three minutes. This resulted in a universe primarily composed of hydrogen and helium, with no heavier elements like gold, carbon, nitrogen, or oxygen. The talk explains that the formation of heavier elements occurred later in the life cycles of stars, which will be discussed in subsequent paragraphs.

The universe began as a smooth distribution of gas that, under the influence of gravity, started to clump together to form structures. This process is observable in the cosmic microwave background radiation, which shows the distribution of matter 380,000 years after the Big Bang. Over time, these clumps grew, leading to the formation of galaxies, the basic building blocks of the universe. The Milky Way, our home galaxy, consists of billions of stars and vast clouds of gas and dust. The talk also discusses the challenges of observing other galaxies due to light pollution and the vast distances involved.

Stars, including our sun, are primarily composed of hydrogen and helium. The core of the sun, under extreme temperatures and pressures, undergoes nuclear fusion reactions where hydrogen atoms combine to form helium, releasing energy in the process. This energy is what powers the sun. The talk explains the difference between fission and fusion reactions, with fission being used in nuclear power plants and fusion powering the sun. The sun is currently halfway through its life, having converted about half of its hydrogen into helium. The talk also touches on the future of the sun, which will eventually run out of fuel and undergo changes leading to its transformation into a red giant star.

The sun will eventually run out of hydrogen fuel and start to die. As the core contracts, the outer layers of the sun will expand, turning it into a red giant star. During this phase, the core will be hot enough to convert helium into carbon and a small amount of carbon into oxygen. However, the sun is not massive enough to create elements heavier than iron. The talk explains that the heavier elements, such as gold and mercury, are formed during the supernova explosion of massive stars. These stars fuse elements up to iron in their lifetime, and the core collapse at the end of their lives leads to the creation of all other elements in a brief, intense period.

The universe exhibits a preference for even-numbered elements, which are more abundant than odd-numbered elements. This is attributed to the nuclear fusion processes in massive stars, where helium serves as a fundamental building block. The talk explains that the fusion of helium with other elements creates a chain of heavier elements, all of which are even-numbered. The most abundant elements in the universe are hydrogen and helium, followed by oxygen and carbon. The talk emphasizes that the elements in our bodies are common in the universe, forged in the stars, and that we are, in essence, made of star stuff.

The atoms in our bodies have a rich history, having been part of multiple stars throughout the universe's history. Initially, these atoms were part of hydrogen and helium in star-forming regions. Over time, they were incorporated into stars, where they underwent various nuclear reactions, eventually forming heavier elements like gold. These elements were dispersed into space when the stars exploded as supernovae. The atoms then became part of the dust and gas that led to the formation of planets and, ultimately, ended up on Earth. The talk poetically describes our connection to the stars and the cyclical nature of atomic existence.

The talk concludes with a reflection on the future of the atoms that make up our bodies. After our death, these atoms will return to the Earth's surface and be recycled through various life forms. Eventually, as the sun reaches the end of its life and expands into a red giant, the outer layers of the Earth will be vaporized, and our atoms will become part of the outer layers of the sun. Following the sun's death, the atoms will be part of a beautiful planetary nebula, eventually finding their way into future generations of stars. The speaker emphasizes the poetic nature of this cosmic recycling, highlighting our profound connection to the universe.

The talk concludes with a question and answer session where the speaker addresses various topics, including the city of Charlottesville's dark sky ordinance, the nature of black holes, and the interaction between black holes and stars. The speaker clarifies misconceptions about black holes, explaining that they only exert a strong gravitational pull at very close distances. The session ends with a reminder of the cosmic nature of our existence and the continuous cycle of our atoms through the universe.