very long full video recording of March 26 talk live streamed at the Central Coast Astronomical Society including Q&A followed by Dave Major's Betelgeuse talk.
This NetLogo animation shows the evolutionary stages of a 25 solar mass star from the main sequence through the late concentric shells of nucleosynthesis to the explosive supernova and remnant neutron star.
The animation starts with the main sequence burning of hydrogen to form helium. The hot dense core uses the CNO process and it is not transparent enough for its energy to radiate away as fast as it is generated. As a result, thermal convection is triggered, producing a massive upwelling of hot gas and a downwelling of gas cooled by transferring energy to the non-fusing outer envelope of the star which transfers energy radiatively. This happens to be the opposite pattern from smaller stars like our sun.
As the star evolves beyond the main sequence, more and more shells of ever greater density and temperature form in the core. Each shell is dominated by nucleosynthesis involving elements made in earlier stages.
The second part of the animation shows what happens if the star had a binary partner that also went supernova and formed a remnant neutron star. This rare combination can lead to a neutron star merger as the stars spiral toward each other by losing energy through the generation of intense gravity waves. These mergers produce heavy but less abundant elements.
Making a video like this is educational because you have to think about whether thermal convection or electromagnetic radiation transports energy within each zone or shell. You have to think about the radius of a fusion core or shell and whether it increases or decreases over time. When does the non-fusing envelope get dispersed? How much gravitational energy is dissipated as waves when neutron stars merge? You have to think about how to use the model to explain the process to people.
Let’s play the video animation – bearing in mind that all models are wrong, but some are useful. This model is just a start - the answers to these questions will require an overhaul of the model. And it needs a narrator to explain what you are seeing.
fast review of We are Stardust animated PowerPoint slide show March 26, 2020
This webpage is under construction.
fall 2019 event flyers
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origin and abundance of Periodic Table elements that form planets
introductory text 2
Scientists have found how planet formation occurs from stardust
Much about planet formation is not understood. Astronomers suspect that planets form from a disk of gas and dust that clumps together over time, to form giant planets. There's just one problem: How do you get something the size of a pebble to form something the size of a planet? A new study suggests the solution has to do with something called "dust traps." Read more: http://www.techinsider.io/
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stardust - element abundances depend on binding energy per nucleon and conditions required for nuclear processes
low mass stars live longer than massive stars that burn hot and die young
stellar origins Wikipedia pdfs
These pdfs of Wikipedia articles describe the types of stars that synthesize elements of the Periodic Table including massive stars, supernovas, neutron stars, black holes, low mass stars, and white dwarfs.
nuclear processes Wikipedia pdfs
These pdfs of Wikipedia articles describe processes that synthesize elements of the Periodic Table
quarks combine to form protons and short lived neutrons
a few microseconds after the Big Bang, our universe had cooled and expanded enough for all of the quarks to condense into baryons, that is protons and neutrons. Protons are the nucleus of the first element hydrogen, so the Periodic Table consisted of one element for several minutes.
During the first second, there was so much radiant energy in the universe that protons could eject a positron and form a neutron, even though the neutron rest mass was slightly greater than the proton's. There were equal numbers of protons and neutrons until the universe cooled enough that neutrons could decay into protons and electrons, but protons were not energetic enough to form neutrons.
Big Bang nucleosynthesis of helium and traces of lithium involves free neutrons
After a few minutes the universe was cool enough that protons and neutrons could fuse into deuterium, tritium, helium 3, and the common helium 4 nuclei, and a trace of the third element lithium. Big Bang fusion was very fast because half of the particles were neutrons which are not repelled by protons.
Since free neutrons decay with a half life of about ten minutes, these larger nuclei could form for about 15 minutes. The free neutrons decayed and the universe cooled to the point that the primordial Big Bang nucleosynthesis ceased. Any remaining free neutrons decayed into protons and electrons.
Nucleosynthesis stopped in the universe for perhaps 100 million years until the interstellar medium cooled enough to form the first stars. The first stars were massive because the interstellar medium could not cool enough to form smaller stars.
massive stars fuse helium to synthesize oxygen and 31 other elements by a mixture of slow and rapid fusion processes
The first generation of stars were massive and lived fast and died young. In other words, they fused numerous elements, exploded as they died, and dispersed their elements, thereby enriching the interstellar medium from which the next generation of stars condensed. All of the oxygen in the universe was formed in massive stars that went supernova as they died.
Massive stars greater than eight solar masses synthesize helium, carbon, oxygen, neon, silicon, sulfur, iron, and others when the iron core collapses, these elements are dispersed and more elements are synthesized.
High Mass Stars: Crash Course Astronomy #31
Massive stars fuse heavier elements in their cores than lower mass stars. This leads to the creation of heavier elements up to iron. Iron robs critical energy from the core, causing it to collapse. The shock wave, together with a huge swarm of neutrinos, blast through the star’s outer layers, causing it to explode. The resulting supernova creates even more heavy elements, scattering them through space. Also, happily, we’re in no danger from a nearby supernova. Sep 10, 2015
triple alpha process synthesizes one carbon from three helium nuclei
alpha ladder from carbon to iron
exploding stars produce cosmic rays which synthesize elements by fission
Exploding stars produced cosmic rays cosmic rays synthesize more lithium and all of the beryllium and boron by fission of more massive nuclei.
binary neutron stars mergers synthesize gold and about 40 more stable elements by rapid neutron fusion
The life cycle of a neutron star - David Lunney
About once every century, a massive star somewhere in our galaxy runs out of fuel. No longer able to produce sufficient energy to maintain its structure, it collapses under its own gravitational pressure and explodes in a supernova. The death of that star is the birth of a neutron star: one of the densest known objects in the universe. David Lunney explores what, exactly, a neutron star is. Nov 20, 2018
What are neutron stars? (Astronomy)
Stars are not eternal and unchanging - they are born, live their lives, and then die. The way a star dies depends on its mass. A low mass star ends as a white dwarf. A high mass star becomes a black hole. But in between, a star becomes a neutron star. In this video we talk about which stars become neutron stars, and the physics behind their formation. Jan 4, 2015
dying low mass stars synthesize most of the carbon and nitrogen and a massive fraction of lithium as well as 18 elements from strontium to bismuth and 12 elements in the lanthanide series by slow neutron fusion over millions and billions of years
Low mass stars started dying at 130 million years. Low mass stars synthesize elements by a slow neutron capture process. After eight billion years, enough low mass stars died and white dwarfs exploded to produce the current mix of elements found today. Enrichment of interstellar space continues as new stars are born and die, but the general characteristics are the same.
exploding white dwarf stars synthesize a massive fraction of the 17 elements from silicon to zinc
Early white dwarfs exploded at one billion years. White dwarf stars may acquire mass from a binary partner and explode and synthesize elements from silicon to zinc by multiple rapid neutron captures by nuclei
What are white dwarfs? (Astronomy)
White dwarfs are dead stars that continue to glow because of heat, not nuclear fusion. Most stars in our universe will end up as a white dwarf star. Join us to learn how white dwarfs are made, what they’re like, how long they’ll shine, and how astronomers detect them. Aug 10, 2016
Big Bang nucleosynthesis
Big Bang nucleosynthesis happened in a matter of minutes while free neutrons were still abundant in the early universe. Neutrons are electrically neutral and are not repelled by positively charged protons, so they can get close enough to fuse. Free neutrons are also generated by merging neutron stars, so they formation of the heaviest elements can also occur rapidly.
This is very different from stellar fusion which takes millions or billions of years because most stars do not have free neutrons and very few protons are energetic enough to overcome their coulombic repulsion. In fact protons only fuse due to quantum tunneling, which allows them to violate energy conservation briefly until they pay it back by forming a lower energy bound state. When protons fuse, some of their energy is used to transform some of them to the more massive neutrons that are found in all nuclei other than hydrogen. This process is illustrated in the animations shown below.
Our NetLogo model illustrates the processes without any physics or time scales
Stellar thermonuclear fusion releases energy when nuclei fuse at extreme densities and temperatures. Nucleosynthesis of protons produces a series of increasingly massive nuclei. The process is very rare and slow for any individual particle, but the extreme mass of a star provides an environment in which massive amounts of energy can be released for billions of years.
The fusionHe101 NetLogo model simulates the three steps of fusion that convert hydrogen nuclei into helium 4 nuclei in the interior of the Sun or a Sun-like star. First two protons fuse to form a hydrogen isotope called a deuteron or deuterium nucleus consisting of one proton and one neutron. Second, a proton fuses with a deuteron to form a helium 3 nucleus consisting of two protons and one neutron. Third two helium 3 nuclei fuse to form the more common isotope, the helium 4 nucleus consisting of two protons and two neutrons with the release of the two extra protons. The number of nuclei decreases in the first two steps and increases in the third step, but the number of nucleons does not change because any proton that is lost is transformed into a neutron.
The three steps are:
1 - H1 + H1 → H2 + e+ + nu and e+ + e- → photon + photon
2 - H1 + H2 → He3 + photon
3 - He3 + He3 → He4 + H1 + H1
The first step is very difficult and rate which is why thermonuclear fusion of hydrogen to helium continues for about ten billion years while the Sun is on the main sequence. The first step also releases a neutrino which is non-interacting and quickly escapes the Sun at the speed of light, carrying off a small amount of energy. This step also creates a positron or anti-electron which carries the positive charge lost when one of the protons turns into a neutron. The positron quickly annihilates itself and an electron, converting their masses into electromagnetic energy via a pair of gamma rays. These photons do not travel far before being absorbed by electrons that disperse the resulting thermal energy to other particles through collisions.
The second step only takes millions of years. This process also releases energy in the form of a photon which is also quickly absorbed by an electron.
Our model has many simplifications compared to the 18000 line Fortran solar evolution model that Dr. Joyce Guzik of Los Alamos National Lab gave us in 2006. The large code provides detailed numerical properties throughout the interior of the Sun, but does not provide an easy visualization of the actual processes. Our model is much simpler and does not provide thermal properties or predictions of rates of reactions, but does help the user visualize the processes and think more deeply about what is going on in the core of the Sun.
Sun fusion slides explains in simplified terms how thermonuclear fusion in the core of the Sun converts hydrogen to helium using PowerPoint animation. This sequence of interactions is the basis of the NetLogo fusion model shown above.
five embedded videos on the origin of the elements
"We are made of star stuff": The Origin of the Elements (Part 1 of 2)
The origin of the chemical elements
The Origin of the Elements
UC Santa Cruz astrophysics department chair Raja Guha Thakurta gave a talk entitled "The Universe of Galaxies: Dark Matter, Cannibalism, Black Holes, Gravity Waves, and the Periodic Table of Elements" on Wednesday October 9 in Spanos Theatre.We are very proud of the fact that Dr. Raja's lecture in Spanos attracted 416 attendees. This reflects well on our community, for which we are very grateful.
Raja illustrated his slide presentation with the latest astronomical images, animations, and videos. This was a free public event.
Dr. Raja discussed how the materials that compose human beings and other life forms were synthesized inside the Sun's ancestral stars. Our dark matter dominated Milky Way galaxy and other galaxies like it serve as chemical recycling plants and are responsible for the richness and complexity of the Periodic Table of elements. He also discussed the lives and times of galaxies: galaxy cannibalism and mergers, black holes, gravitational waves, and the growth and evolution of galaxies from the tiniest ripples in the fabric of the early Universe.
Raja Guha Thakurta is Professor and Department Chair of Astronomy/Astrophysics at the University of California Santa Cruz. He studies the formation and evolution of galaxies large and small, with a focus on the assembly of their dark matter, dynamics, merger history, chemical enrichment, and star formation history. He makes extensive use of the Hubble Space Telescope and Keck telescopes in his research.
He is the founder and faculty director of the successful Science Internship Program, a program in which high school students are mentored by UCSC researchers and work on cutting-edge STEM research projects. He received his Ph.D. in Astrophysical Sciences from Princeton University in 1989.