Astro Lecture 3 Flashcards
How did the universe transition from homogeneous to having discrete objects?
Small over-densities (variations of about 1 part in 100,000) in the early universe collapsed under gravity, creating a runaway process that formed regions of high density where galaxies and stars formed.
What is the gravitational cascade process?
A process where small gravitational pulls toward slightly denser regions increase as more mass falls in, creating a runaway effect that leads to the formation of galaxies and stars.
What is the end state of the universe’s structure compared to its beginning?
The universe transitions from initially fairly homogeneous to very clumpy, with matter concentrated in galaxies, clusters, and filaments.
What is the basic process of star formation?
A cloud of gas (mostly hydrogen and helium) collapses under its own weight, increasing in spin and temperature until the center becomes hot and dense enough for thermonuclear fusion to begin.
What is the most important property determining a star’s life?
Mass is the key property that determines how hot a star burns, how long it lives, and how it will eventually die.
What is blackbody radiation in relation to stars?
Blackbody radiation is the thermal radiation emitted by stars, with each curve characterized by a single temperature. Hotter stars emit more energy at shorter wavelengths (bluer light).
What is the Hertzsprung-Russell diagram?
A chart that plots stars’ luminosity against temperature, showing the Main Sequence where stars spend most of their lives, with a star’s position determined by its mass.
What is the relationship between a star’s mass and its lifespan?
More massive stars burn much hotter and brighter but have significantly shorter lifespans than less massive stars.
What are the major stages of stellar evolution?
Star formation from collapsing gas cloud, hydrogen fusion in the core, hydrogen fusion in outer shells, and finally shedding outer layers (for smaller stars) or exploding (for larger stars).
What is the fate of low mass stars (up to ~1 solar mass)?
They burn all hydrogen fuel, become red giants, and eventually shed their outer layers as planetary nebulae while their cores collapse into white dwarfs.
What is a red giant?
A large, relatively cool star that has expanded because fusion is happening closer to its surface, and has begun to lose mass.
What is a planetary nebula?
A beautiful, illuminated gas cloud formed when a dying low-mass star expels its outer layers (despite the name, it’s unrelated to planets).
What is a white dwarf?
A hot, dense remnant core of a low-mass star, composed of degenerate matter that cools over time.
What happens to high mass stars (>10 solar masses) at the end of their lives?
They burn hydrogen and progressively heavier elements up to iron, then collapse rapidly, creating a super-heavy core while outer layers explode as a supernova.
What are the possible remnants of high mass stars?
Depending on the initial mass, the core becomes either a neutron star or a black hole.
What is a neutron star?
An extremely dense object composed of tightly packed neutrons, often observed as pulsars that emit beams of radiation while rotating.
How does a black hole form?
When a star’s mass is so concentrated that the escape velocity exceeds the speed of light (v > c), creating a region from which nothing, not even light, can escape.
How are heavy elements created and distributed in the universe?
Supernovae explosions create and distribute heavy elements into space, providing material for the next generation of stars and planets.
Why is the phrase ‘We are made of star dust’ scientifically accurate?
The heavy elements in our bodies were created inside stars and distributed through space by supernovae explosions before being incorporated into our solar system.
