The Life and Death of Stars
01: Why the Stellar Life Cycle Matters
View the life cycle of a star in its broadest context, seeing how stars serve as agents of alchemy, transforming the simplest element-hydrogen-into the panoply of heavier elements that compose life and all other material objects in the universe.
02: The Stars' Information Messenger
Discover that there is much more to light than what we can see with our eyes. Investigate the properties of light and the electromagnetic spectrum, which extends from gamma rays to radio waves. Then learn how astronomers read a star's spectrum to determine the star's elemental composition.
03: Measuring the Stars with Light
Uncover more information encoded in starlight, learning how color and patterns of emission and absorption reveal the surface temperature of a star and its motion relative to Earth. Examine the scientific laws that explain stellar spectra, and find out how stellar distances are measured.
04: Stellar Nurseries
Probe the places where stars begin their lives: stellar nurseries. Use what you've learned about light to interpret the incredible colors and sculpted shapes in glowing clouds of gas and dust. See how star death leads to a new generation of stars. Close with a virtual fly-through of the stellar nursery in the Orion Nebula.
05: Gravitational Collapse and Protostars
Chart the stages of star birth in stunning astronomical images. From Bok globules and Herbig-Haro objects to protoplanetary disks, these phases develop as gravity brings together material within denser regions of a stellar nursery. Clumps of matter eventually collapse into stars, which often include surrounding planetary systems.
06: The Dynamics of Star Formation
Hundreds of stars can form inside a single cloud of collapsing gas and dust. Zoom in on the intricate details of this process. First, watch a computer simulation of star formation. Then, see how double, triple, and other gravitationally bound combinations of stars arise.
07: Solar Systems in the Making
Follow the formation of newborn planets as they jockey for position close to their parent stars. Computer simulations show how some planets can be ejected out of their solar systems. Such models suggest that our sun and its planetary system might have looked markedly different in the past than it does now.
08: Telescopes-Our Eyes on the Stars
Focus on the instruments that observe and measure stars: telescopes. Investigate the major types and the detectors they use to extract the maximum amount of information from starlight. Telescopes on Earth and in space can survey the entire range of the electromagnetic spectrum.
09: Mass-The DNA of Stars
Learn how mass is like a star's DNA, as it determines all of a star's physical characteristics. Astronomers can measure a star's mass by observing another star in orbit around it. Explore the Hertzsprung-Russell diagram, which shows that stars of different masses fall into well-defined classes.
10: Eclipses of Stars-Truth in the Shadows
Investigate the remarkable usefulness of eclipses. When our moon passes in front of a star or one star eclipses another, astronomers can gather a treasure trove of data, such as stellar diameters. Eclipses also allow astronomers to identify planets orbiting other stars.
11: Stellar Families
Survey the two major types of star clusters. Open clusters typically form within the disk of a galaxy and represent recent generations of stars, enriched in heavier elements. By contrast, globular clusters form a halo around the centers of galaxies and are some of the most ancient stars in the universe.
12: A Portrait of Our Star, the Sun
Explore the nearest star, the sun, in an imaginary voyage through its fiery photosphere down to the center. Discover the sun's rich inner structure, with strata ranging from the extremely hot and dense core-denser than solid lead-to the more rarefied outer layers.
13: E = mc2-Energy for a Star's Life
Probe the physics of nuclear fusion, which is the process that powers stars by turning mass into energy, according to Einstein's famous equation. Then examine two lines of evidence that show what's happening inside the sun, proving that nuclear reactions must indeed be taking place.
14: Stars in Middle Age
Delve deeper into the lessons of the Hertzsprung-Russell diagram, introduced in Lecture 9. One of its most important features is the main sequence curve, along which most stars are found for most of their lives. Focus on the nuclear reactions occurring inside stars during this stable period.
15: Stellar Death
Stars like the sun end as white dwarfs, surrounded by an envelope of expelled material called a planetary nebula. Explore the complicated and beautiful structure of these dying outbursts. Then investigate the spectacular end of the most massive stars, which explode as supernovae, forging the elements of life in their violent demise.
16: Stellar Corpses-Diamonds in the Sky
Analyze three major types of stellar remains. Low mass stars like the sun leave behind white dwarfs, composed of carbon in a compact diamond-like state. Heavier stars collapse into super-dense neutron stars. And stars weighing more than 20 solar masses end as bizarre black holes.
17: Dying Breaths-Cepheids and Supernovae
Stars vary in brightness during their final phases. Study two phenomena that allow astronomers to measure distances with great accuracy across vast reaches of space: Cepheid variable stars and white dwarf supernovae. Zoom in on the processes that produce these valuable cosmic yardsticks.
18: Supernova Remnants and Galactic Geysers
Explore amazing images of the remnants of supernova explosions, charting how these cosmic catastrophes unfold as if in slow motion. Expanding clouds of supernova debris can trigger new star formation nearby and even carve enormous chimney-like structures in a galaxy.
19: Stillborn Stars
Follow the search for brown dwarfs-objects that are larger than planets but too small to ignite stellar fires. Hear about Professor Stassun's work that identified the mass of these elusive objects, showing the crucial role of magnetism in setting the basic properties of all stars.
20: The Dark Mystery of the First Stars
Join the hunt for the first stars in the universe, focusing on the nearby "Methuselah" star. Explore evidence that the earliest stars were giants, even by stellar standards. They may even have included mammoth dark stars composed of mysterious dark matter.
21: Stars as Magnets
Because stars spin like dynamos, they generate magnetic fields-a phenomenon that explains many features of stars. See how the slowing rate of rotation of stars like the sun allows astronomers to infer their ages. Also investigate the clock-like magnetic pulses of pulsars, which were originally thought to be signals from extraterrestrials.
22: Solar Storms-The Perils of Life with a Star
The sun and stars produce more than just light and heat. Their periodic blasts of charged particles constitute space weather. Examine this phenomenon-from beautiful aurorae to damaging bursts of high-energy particles that disrupt electronics, the climate, and even life.
23: The Stellar Recipe of Life
Survey the periodic table of elements, focusing on the elements that are vital to life. From carbon, oxygen, and nitrogen to phosphorous, copper, and zinc, virtually every constituent of life was forged in a star during some phase of its life cycle.
24: A Tale of Two Stars
Close your introduction to stellar evolution by contrasting the life cycles of two markedly different stars: one like our sun and another 10 times more massive. Professor Stassun compares their histories to milestones in the lives of humans, bringing a personal dimension to the science of stars.