RES.8-007 | Fall 2019 | Undergraduate

Cosmic Origin of the Chemical Elements

Videos

 

In Episode 4, Professor Frebel describes how the old stars formed from gas enriched by only one or few supernovae and younger stars, like the sun, formed from gas enriched by perhaps a thousand events.

Anna Frebel, Associate Professor of Physics at MIT, studies the chemical and physical conditions of the early universe. Often she is asked what her work is all about and what an astronomer does when using a telescope. She addresses these questions at length in her popular science book Searching for the Oldest Stars*. But at some point, she decided it would be fun to make bite-sized explanations of the key topics that people could watch independently or as a supplement to the book.

The result is this eleven-episode series of brief videos, shot over the course of two days at MIT. Professor Frebel uses a lightboard** because it allows her to address her viewers directly, unlike a traditional blackboard which forces the instructor to turn his or her back to the audience while writing on the board.

Whether or not you already have any prior knowledge of astronomy, and whatever your age and background, Professor Frebel hopes these videos will help you understand her passion for old stars and space science and will inspire you to learn more about our beautiful universe.

* Frebel, Anna. Searching for the Oldest Stars: Ancient Relics from the Early Universe. Princeton University Press, 2019. ISBN: 9780691165066.

** The technology used in the MIT lightboard flips the video image left-to-right so that the words written on the board appear correctly rather than being reversed as would ordinarily be the case with writing seen through glass.

Everything around us is made from different elements: carbon, silicon, iron, and all the other elements from the Periodic Table. But have you ever wondered where all these elements came from?

Associated Book Chapters from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 1: What Is Stellar Archaeology?
  • Chapter 2: Two Centuries of Pursuing Stars

For astronomers, spectrographs mounted on the largest telescopes are a primary tool to carry out their work. This is particularly true for stellar archaeology studies. This way the data needed for a chemical abundance analysis—stellar spectra—can be obtained. Some of the best telescopes in the world are the twin Magellan telescopes, which each have a mirror that is 6.5m in diameter. They are located in Chile in the Southern Hemisphere where the night sky is particularly bright and beautiful to watch, for astronomers and lay people alike! Get a peek into what it means when astronomers go observing. 

Associated Book Chapters from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 7: Tales Told by Light
  • Chapter 8: Let’s Go Observe Some Stars!
  • Chanpter 10: Finding the Oldest Stars
  • Chapter 11: At the End of a Cosmic Journey

See how all the topics discussed in this mini lecture series are connected. Because in the universe, everything depends on everything! And that’s a beautiful thing! 

Associated Book Chapters from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 1: What Is Stellar Archaeology?
  • Chapter 3: Stars, Stars, More Stars
  • Chapter 7: Tales Told by Light
  • Chapter 9: The Chemical Evolution of the Early Universe
  • Chapter 11: At the End of a Cosmic Journey

After the Big Bang, the universe was composed of just hydrogen, helium, and tiny amounts of lithium. With time, heavier elements were forged in the many generations of stars. After about 8 billion years, the Sun was born, from gas that contained 1.4% of heavier elements. Today, this amount has increased to 2%. The Astronomer’s Periodic Table depicts the three most important constituents of the universe: X (= hydrogen), Y (= helium), and Z (= metals). (In the astronomical sense, “metals” refers to all the elements except hydrogen and helium.) 

Associated Book Chapters from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 1: What Is Stellar Archaeology?
  • Chapter 2: Two Centuries of Pursuing Stars
  • Chapter 3: Stars, Stars, More Stars

The first stars formed from the primordial gas of just hydrogen and helium left behind after the Big Bang. Later generations of stars formed from gas enriched in metals that were previously forged in the cores of the first stars. This process of element production and enrichment of the surrounding gas is called the chemical evolution. Among the second and later generations of stars were low mass stars with long lifetimes that make them still observable today. This allows astronomers to study how elements were created over cosmic time. 

Associated Book Chapters from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 3: Stars, Stars, More Stars
  • Chapter 4: Stellar Evolution—From Birth to Death
  • Chapter 9: The Chemical Evolution of the Early Universe

The first stars forged metals heavier than hydrogen and helium in their cores to produce energy to shine. These heavier elements were then expelled into space once the stars exploded as the first massive supernovae. Since then, massive exploding stars have contributed elements to the universe thus setting in motion the cosmic chemical evolution. Consequently, old stars formed from gas enriched by only one or few supernovae and younger stars like the sun formed from gas enriched by perhaps a thousand events. 

Associated Book Chapters from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 3: Stars, Stars, More Stars
  • Chapter 4: Stellar Evolution—From Birth to Death
  • Chapter 9: The Chemical Evolution of the Early Universe
  • Chapter 10: Finding the Oldest Stars

The oldest stars in the Milky Way are 13 billion years old and still shining today. They are used to study the early universe because their chemical composition tells about the gas from which they formed a long time ago. This is called stellar archaeology.

Associated Book Chapter from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 1: What Is Stellar Archaeology?

Stars shine for millions and billions of years. This is sustained by ongoing fusion of hydrogen and other elements in the core region of each star. Every time four hydrogen atoms fuse through a series of steps into a helium nucleus, a tiny bit of energy is released. Eventually, once iron has been produced in the core, fusion is no longer possible. The star cannot produce any more energy and thus has to explode as a gigantic supernova.

Associated Book Chapters from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 3: Stars, Stars, More Stars
  • Chapter 4: Stellar Evolution—From Birth to Death
  • Chapter 6: Welcome to Our Milky Way

Astronomical observations of stars only capture the properties of the surface. The inside remains hidden. But with the help of physics and our understanding of element fusion, we can piece together what’s going on. Learn how the Hertzsprung-Russell diagram is a reflection of the processes that occur in the center of stars. This is a different take on element production, namely how it influences the surface properties throughout the stars’ lifetime from birth to supernova explosion.

Associated Book Chapters from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 3: Stars, Stars, More Stars
  • Chapter 4: Stellar Evolution—From Birth to Death
  • Chapter 6: A Milky Way above Us

The technique of spectroscopy allows astronomers to study the composition of stars. The star light is split up into its rainbow colors. But little bits of colors are actually missing in there. Different atoms within the surface layers of the star have absorbed this missing light. This allows astronomers to figure out what elements and how much of them are present in the star. 

Associated Book Chapter from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 7: Tales Told by Light

How did elements heavier than iron form? Elements like silver, gold, platinum, lead, and the many others from the bottom half of the periodic table are created when many, many neutrons are suddenly added to iron and other atoms. Two main processes describe this heavy element formation which occurs in red giant stars and neutron star mergers.

Associated Book Chapter from Searching for the Oldest Stars: Ancient Relics from the Early Universe

  • Chapter 5: Neutron-Capture Processes and the Heaviest Elements

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